Research Article A DFT Study of Some Structural and...

Research ArticleA DFT Study of Some Structural andSpectral Properties of 4-MethoxyacetophenoneThiosemicarbazone and Its Complexes withSome Transition Metal Chlorides Potent Antimicrobial Agents

Julius Numbonui Ghogomu and Nyiang Kennet Nkungli

Laboratory of Noxious Chemistry and Environmental Engineering Department of Chemistry Faculty of ScienceUniversity of Dschang PO Box 67 Dschang Cameroon

Correspondence should be addressed to Julius Numbonui Ghogomu ghogsjujuhotmailcom

Received 12 June 2016 Revised 4 October 2016 Accepted 13 October 2016

Academic Editor Kittusamy Senthilkumar

Copyright copy 2016 J N Ghogomu and N K Nkungli This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Recent studies have shown that 4-methoxyacetophenone thiosemicarbazone (MAPTSC) and its complexes with some transitionmetal chlorides are potent antimicrobial agents To deepen the understanding of their structure-activity relationships necessary forrational drug design their structural and spectral properties along with thione-thiol tautomerism of MAPTSC have been studiedherein using the density functional theory (DFT) From our results the thione tautomer of MAPTSC is more stable than the thiolcounterpart in ethanolic solution and thione-to-thiol tautomerization is highly precluded at ambient temperature (25∘C) by a highbarrier height asymp4641 kcalmol MAPTSC can therefore exist as a mixture of the thione (major) and thiol (minor) tautomers inethanolic solution at room and higher temperatures Conformational analysis has revealed five possible conformers of the thionetautomer of which two are stable enough to be isolated at 25∘C Based on our computed values of MAPTSC-metal(II) bindingenergies enthalpies and Gibbs free energies the thione tautomer of MAPTSC exhibits a higher affinity for the d8 metal ions Ni(II)Pd(II) and Pt(II) and can therefore efficiently chelate them in chemical and biological systems Natural population analysis hasrevealed ligand-metal charge transfer in the MAPTSC complexes studied A good agreement has been found between calculatedand experimentally observed spectral properties (IR UV-Vis and NMR)

1 Introduction

The coordination chemistry of thiosemicarbazones (TSCs)has recently attracted considerable attention because of theirvariable bonding modes structural diversity nonlinear opti-cal properties and ion-sensing abilities [1 2] TSCs constitutea distinguished class of biologically active molecules byvirtue of their anticancer antiviral antibacterial antifungalantitumor antitubercular and antileprosy activities [3 4]They are commonly used as antiparasitic antimalaria andantiamoebic agents Their biological activities are attributedto their ability to form chelates with metal ions in biologicalsystems and the presence of the imine group (minusN=CHminus) intheir molecular structures [5 6] It is well established that

the transition metal complexes of TSCs are more biologicallyactive than the free ligands probably due to the increasedlipophilicity (which controls the rate of entry into the cell)of the complexes The presence of metal ions does not onlyimprove upon their biological activities selectivity chemicalstability and their usually low water solubility but alsomitigates their side effects [7]

Recently 4-methoxyacetophenone thiosemicarbazone(MAPTSC) and its transition metal chloride complexeshave been synthesized characterized and found to exhibitstrong to moderate antimicrobial activities [8 9] To the bestof our knowledge the impact of thione-thiol tautomerismon the metal-coordinating ability of MAPTSC has not yetbeen investigated The transition metal chloride complexes

Hindawi Publishing CorporationAdvances in ChemistryVolume 2016 Article ID 9683630 15 pageshttpdxdoiorg10115520169683630

2 Advances in Chemistry

of MAPTSC currently studied were synthesized at 78∘Cin ethanolic solution [9] a temperature high enough toenhance thione-to-thiol tautomerization of MAPTSC sincethe equilibrium involved is temperature controlled [10]Apparently only the complexes of the thione tautomer werereported to be synthesized and characterized althoughthose of the thiol tautomer might have been formed as wellX-ray diffraction studies which are capable of providingmore insight into the nature of these complexes have notbeen carried out till date Moreover an in-depth analysisof the experimentally determined spectral data for thesemolecules has not yet been performed To address theseissues quantum chemical calculations are more appropriateand elegant compared to experimental methods Theresults obtained from such calculations are commonly usednowadays to investigate the relationship between electronicstructure and spectral properties [11] We have pursuedtheoretical studies on these molecules in order to providedetailed information on their structures properties andrelative stability of the thione-thiol tautomers of MAPTSCall of which is essential for better understanding of theirstructure-activity relationships as well as their reactivityin chemical and biological systems In this regard thecurrent study is aimed at providing a detailed analysis of thestructural and spectral properties of MAPTSC along withsome of its transition metal chloride complexes in a bidto facilitate rational drug design using these molecules asprecursors

In this work we set out mainly to theoretically optimizethe geometries of the thione and thiol tautomers ofMAPTSCdetermine their relative stability and possible conformersinvestigate their metal-coordinating abilities and perform adetailed structural and spectral analyses of the tautomersalong with their Ni(II) Pd(II) Pt(II) and Zn(II) chloridecomplexes In a strict sense we have calculated and analyzedthe geometric parameters (bond lengths bond angles anddihedral angles) atomic charge distribution IR vibrationalmodes NMR chemical shifts and electronic absorptionspectra of thesemolecules FurthermoreMAPTSC-metal(II)binding energies enthalpies and Gibbs free energies as wellas thermodynamic parameters associated with thione-thioltautomerism and rotational isomerism of MAPTSC havebeen studied To determine the suitability of our theoreticalapproaches relevant experimental data has been comparedwith our theoretical results The density functional theory(DFT) method has been chosen for this study because itis faster and less computationally intensive takes betteraccount of electron correlation and has a precise accuracyin reproducing experimental data [12] In addition the DFThas been proven to be a very reliable method for transitionmetal complexes [13] and is generally considered to be a goodcompromise between accuracy and computational time

2 Computational Details

All quantum chemical calculations were performed withthe Gaussian 09W computational package [14] The pre-and postprocessing of data were carried out with Gauss

View 508 [15] and Multiwfn 336 [16] The ground stategeometries of the molecules studied were optimized withoutconstraints of any sort using the Beckersquos three-parameterLee-Yang-Parr (B3LYP) DFT functional [17] This functionalwas chosen because it produces relatively good geometriesof transition metal-containing molecular systems [18] Whilethe geometries of the thione-thiol tautomers and conformersofMAPTSCwere fully optimized at the B3LYP6-31++G(dp)level of theory those of the transition metal chloride com-plexes of the thione tautomer of MAPTSC were optimized atthe B3LYP6-31++G(dp)(SDD for metal ions) level of the-ory Here SDD stands for the small core Stuttgart-Dresdeneffective core potential which reduces computational costand includes some relativistic effects in the calculations Toconfirm the fully optimized geometries of the moleculesas local minima on their potential energy surfaces (PES)harmonic vibrational frequencies were computed at the samelevel of theory as that used for geometry optimizationNo imaginary frequencies were obtained for any of theoptimized geometries ascertaining that they are minima ontheir respective PES The restricted closed-shell Kohn-Shammodel was adopted for all theoretical calculations reportedin this paper since all molecules studied are closed-shellsystems

The effects of the bulk solvent environment on geom-etry configurations and absorption spectra were taken intoaccount by means of the polarizable continuum model(PCM) using the integral equation formalism approach (IEF-PCM) Time-dependent density functional theory (TD-DFT)calculations at the CAM-B3LYP6-31G(dp)(LANL2DZ formetal ions) level of theory were performed in order to simu-late the UV-Vis spectra of the molecules under investigationHere the effective core potential LANL2DZ was preferredover SDD for the metal ions because LANL2DZ resulted insignificant speed-ups of the TD-DFT calculations but yieldedresults that agreed remarkably with experimental valuesMoreover negligible discrepancies were observed betweenthe results obtained by employing LANL2DZ for the metalions and those obtained by using SDD for these metal ionsin the complexes currently studied Isotropic NMR shieldingconstants were calculated by the gauge independent atomicorbital (GIAO) method

3 Results and Discussion

31 Molecular Geometry of MAPTSC Before computing themolecular properties of metal complexes it is necessary toanalyze the molecular structures of the ligands in orderto identify their stable tautomers and conformers In thisregard we have carried out tautomerism and conformationalanalyses on MAPTSC

311 Hydrogen Atom Migration Studies and TautomerismAnalysis on MAPTSC Thione-to-thiol tautomerism ofMAPTSC in ethanol (elucidated in Figure 1) was simulatedvia hydrogen atom migration studies During the processH23 migrates from the hydrazinic nitrogen (N22) to thethionic sulfur (S25) In Figure 1 A1 and A2 represent the

Advances in Chemistry 3

Conformer IThione tautomer (A1)

Conformer IIThione tautomer (A1) Thiol tautomer (A2)

Figure 1 The thione-to-thiol tautomerization process for MAPTSC

A1Conformer II

A1Conformer I

A2

TS0

minus102658

minus102656

minus102654

minus102652

minus102650

minus102648

Ener

gy (H

artre

e)

350 300 250 200 150 100400Hydrogen atom migration coordinate (H23ndashS25 bond distance)

EA = 4641kcalmol

EA = 3251kcalmol

Figure 2 PES scan curve for hydrogen atommigration inMAPTSCsimulated at the B3LYP6-31G(dp) level of theory in ethanol assolvent

thione and thiol tautomers of MAPTSC respectively Inthe course of the PES scan for H23 atom migration theH23ndashS25 bond was chosen as the reaction coordinate ThePES scan was performed by shrinking the bond distancebetween H23 and S25 to smaller values at regular intervalsof 0227 A At each interval geometry optimization wasperformed at the B3LYP6-31G(dp) level of theory ThePES scan curve for the hydrogen atom exchange process(Figure 2) has revealed that thione-to-thiol tautomerizationof MAPTSC is preceded by free rotation about the N22ndashC24bond which converts conformer I of A1 into conformerII This rotation occurs concomitantly with reduction inthe bond distance between H23 and S25 This is thenfollowed by intramolecular abstraction of H23 by S25 Adouble bond rearrangement from C24=S25 to N22ndashC24immediately occurs transforming conformer II of the ligandinto A2 via the transition state designated TS0 was inFigure 2 TS0 was confirmed a first-order saddle point onthe PES by normal mode analysis at B3LYP6-31G(dp) level

Table 1 The relative energies (Δ119864tot kcalmol) HOMO-LUMOenergy gaps (Δ119864H-L kcalmol) enthalpies of formation (Δ119867119900119891kcalmol) and Gibbs free energy of formation (Δ119866119900119891 kcalmol) ofthe thione and thiol tautomers of MAPTSC calculated at B3LYP6-31G(dp) level of theory at room temperature (298K) in ethanol assolvent

Medium Tautomer Δ119864tot Δ119864H-L Δ119867119900119891 Δ119866119900119891

Gas Thione minus187 minus209 minus187 minus206Thiol 000 000 000 000

Ethanol Thione minus932 889 minus932 minus934Thiol 000 000 000 000

DMSO Thione minus974 850 minus974 minus994Thiol 000 000 000 000

of theory which yielded one imaginary wavenumber ofvalue minus44958 cmminus1 (unscaled) for ](S25ndashH23) stretchingvibration The barrier heights (119864119860) for thione-to-thiol andthiol-to-thione tautomerization were found to be asymp4641and 3251 kcalmol respectively signifying that thione-thioltransformations of MAPTSC are nearly hindered in ethanolat room temperature

In order to determine the most stable tautomer ofMAPTSC the relative stability of A1 andA2was investigatedon the basis of their total ground state energies HOMO-LUMO energy gaps enthalpies and Gibbs free energiesof formation The relative values of these thermodynamicparameters calculated in gas and solvent phases are pre-sented in Table 1 for comparison It is evident from thehydrogen atom migration curve in Figure 2 that A1 is lowerin energy than A2 implying that the thione tautomer ismore stable than the thiol form The relative energies (Δ119864tot)of the tautomers in gas and solvent phases have confirmedthe thione tautomer of MAPTSC as being more stable thanthe thiol counterpart by 187 932 and 974 kcalmol ingas phase ethanol and water respectively The HOMO-LUMO energy gap (Δ119864H-L) is generally used to determinethe kinetic stability of a molecular entity A molecule with asmall HOMO-LUMO energy gap is more polarizable and is


generally associated with a high chemical reactivity and lowkinetic stability [12] The values of Δ119864H-L for the tautomershave shown that the thione form is chemically harder thanthe thiol counterpart in both ethanol and water by 889 and850 kcalmol respectively while in the gas phase the latteris chemically harder than the former by 209 kcalmol Hencethe thione tautomer is more kinetically stable than the thiolform in the solvents but less kinetically stable than the thioltautomer in the gas phase This is in accordance with themaximum hardness principle which states that moleculesarrange themselves to be as hard as possible

The Gibbs free energy change for thiol-to-thione tau-tomerization isminus206minus934 andminus994 kcalmol in gas phaseethanol and water respectively It is clear from these valuesthat at room temperature this conversion is spontaneousand thermodynamically favored in both gas and solventphases Moreover the enthalpy change for this process isminus187 minus932 and minus974 kcalmol in gas phase ethanol andwater respectively showing that the process is exothermicin each medium From the foregoing results the thionetautomer of MAPTSC is considered more thermodynami-cally stable than the thiol counterpart The latter tautomeris less stable because the H23 atom of the thiol groupis orientated such that its intramolecular abstraction bythe azomethine nitrogen N22 is facilitated thus enhancingthiol-to-thione tautomerization The orientation of the H23atom of the hydrazinic group in conformer I of the thionetautomer is such that its intramolecular abstraction by thethionic sulfur S25 is highly precluded Hence thiol-to-thione tautomerization of MAPTSC is advantageous overthione-to-thiol conversion resulting in the thione tautomerbeing more stable than the thiol form Based on the resultsobtained from both hydrogen atom migration and thermo-dynamic parameters it can be concluded that the thionetautomer is the most stable form of MAPTSC in both gasand solvent phases findings which are consistent with theliterature [5]

312 Conformational Search and Analysis on MAPTSCMolecular geometry and conformational analysis play avery important role in determining structure-activity rela-tionships [19] From the hydrogen atom migration process(Section 311) it is clear that free rotation about the covalentbond linkingN22 andC24 in the TSCmoiety ofMAPTSC is aprerequisite for thione-thiol tautomerization Such a rotationis possible inA1 owing to the flexibility of theN22ndashC24 singlebond but impossible inA2 due to the rigidity of the N22=C24double bond Consequently a relaxed conformational searchhas been performed only on the PES of A1 by varying thedihedral angles 1206011(N21ndashN22ndashC24ndashS25) and 1206012(C8ndashC9ndashC16ndashC17) individually from 0∘ to 360∘ at constant steps of 10∘ Thegeometry at each step was optimized at B3LYP6-31G(dp)level of theory The conformational scan curves generated bytorsion about 1206011(N21ndashN22ndashC24ndashS25) and 1206012(C8ndashC9ndashC16ndashC17) are plotted on the same axes (Figure 3) These scancurves have revealed five possible conformers of A1 denotedIndashV as shown in Figure 3 The optimized geometries of theseconformers are displayed in Figure 4

Ener

gy (H

artre

e)

minus1026545

minus1026550

minus1026555

minus1026560

minus1026565

minus1026570

minus1026575

minus1026580

TS1TS2

TS3 TS4

II

II

III IV V

minus50 0 50 100 150 200 250 300 350 400

Dihedral angles 1206011(N21ndashN22ndashC24ndashS25)and 1206012(C8ndashC9ndashC16ndashC17)

1206011(N21ndashN22ndashC24ndashS25)1206012(C8ndashC9ndashC16ndashC17)

Figure 3 PES scan curves obtained by varying the dihedral angles1206011(N21ndashN22ndashC24ndashS25) (yielding conformers I and II) and 1206012(C8ndashC9ndashC16ndashC17) (yielding conformers I III IV and V) from 0∘ to 360∘

As depicted in Figure 3 the transformations conformerI rarr conformer II conformer II rarr conformer I con-former I rarr conformer III and conformer IV rarr con-former V occur via the transition states designated TS1TS2 TS3 and TS4 respectively (their geometries are shownin Figure S1 of Supporting Information available onlineat httpdxdoiorg10115520169683630) These transitionstates were confirmed first-order saddle points on the PESby normal mode analysis studies at B3LYP6-31G(dp) levelof theory and in each case one imaginary wavenumber ofvalue minus9527 minus9404 minus4676 and minus5321 cmminus1 (unscaled) wasobtained for TS1 TS2 TS3 and TS4 respectively The afore-mentioned transformations also proceed across the rotationalbarrier heights 1408 1807 670 and 675 kcalmol respec-tively (a detailed analysis of these barrier heights is presentedin Table S2 of Supporting Information)These barrier heightsare accessible at room temperature (25∘C) signifying thatthe five conformers of A1 can exist at this temperatureAlthough all of the conformers are possible at 25∘C notall of them can be isolated in appreciable amounts at thistemperature The barrier heights for conformer I rarr con-former II and conformer II rarr conformer I conversions arehigh enough to permit their isolation at 25∘C in appreciablequantities However the low barrier height for the conversionof conformer I to conformer III reduces the amount ofconformer I that could be isolated at 25∘C It is obvious fromFigure 3 that rapid conversion of conformer III to conformerIV occurs at ambient temperature The barrier height forthe transformation of conformer IV to conformer V is toolow rendering the isolation of the former almost impossibleat room temperature It is also clear from Figure 3 thatconformerV is rapidly converted into conformer ITherefore


Conformer I Conformer II Conformer III

Conformer VConformer IV

Figure 4 Optimized geometries of the conformers of A1 obtained by varying the dihedral angles 1206011(N21ndashN22ndashC24ndashS25) (yieldingconformers I and II) and 1206012(C8ndashC9ndashC16ndashC17) (yielding conformers I III IV and V) from 0∘ to 360∘

of the five conformers of A1 only conformers I and II can beisolated in relatively high yields at room temperature

The computed relative energies of the conformers I and III and III I and IV and I and V are minus62489 minus00036 00017and minus00010 kcalmol respectively (a detailed analysis ofthese relative energies is presented in Table S2 of SupportingInformation) It is worth noting here that the relative energyof any pair of conformers 119909 and 119910 has been calculatedas energy of 119910 minus energy of 119909 In a case where 119910 is lowerin energy than 119909 the relative energy is negative and ifotherwise the relative energy is positive On this basis itis clear that conformer II is much lower in energy thanconformer I Compared to conformer I conformers III andV are slightly lower in energy whereas conformer IV isslightly higher in energy It is therefore obvious from these

relative energies that among the five possible conformers ofA1 at room temperature conformer II is the most stable andthe rest of the conformers are of approximately at the samestability

32 Molecular Geometries of the Complexes Studied Themore stable thione tautomer of MAPTSC was preferredover the less stable thiol form in the molecular struc-tures of the complexes The ground state geometries ofthe complexes [Ni(A1)Cl2] (B) [Pd(A1)Cl2] (C) [Pt(A1)Cl2](D) and [Zn(A1)Cl2] (E) were optimized at the B3LYP6-31++G(dp)(SDD for metal ions) in gas and solvent phaseswithout constraints on symmetry bond lengths bond anglesor dihedral anglesThe gas phase optimized geometries of BndashE are presented in Figure 5


(B) (C)

(E)(D)

Figure 5 Optimized geometries of [Ni(A1)Cl2] (B) [Pd(A1)Cl2] (C) [Pt(A1)Cl2] (D) and [Zn(A1)Cl2] (E) at B3LYP6-31++G(dp)(SDDfor metal ions) level of theory in gas phase

Selected gas phase geometric parameters (bond lengthsbond angles and dihedral angles) in the TSC moieties of allmolecules studied and around the central metal ions in thecomplexes are listed in Table S3 (Supporting Information)In general the neutral form of any TSC (thione tautomer)contains a formal CndashS double bond of length 167ndash172 Awhile the deprotonated thiol form possesses a formal CndashS single bond of length 171ndash180 A [20] In the case ofMAPTSC the calculatedCndashS bond lengths in the thione form(1665 A) and thiol form (1785 A) are in good agreement withliterature valuesThe CndashN and NndashN bond lengths in the TSCmoieties of all molecules studied are very similar (asymp14 A) andlie between the optimal CndashNNndashN bond length (15 A) andthe optimal C=NN=N bond lengths (13 and 12 A resp)This is a clear indication of extensive electron delocalizationwithin the TSC moiety which helps to improve upon thesecond harmonic generation (SHG) efficiency of MAPTSCand its metal complexes The bond lengths R1(C24ndashS25)R4(N22ndashN21) and R5(C16ndashN21) are longer in the complexesthan in the free ligand A1 This can be attributed to thecoordination of S25 and N21 to the central metal ions Themetal-ligand bond lengths in the complexes are similar andare averagely 225 A

It is clear from Table S3 that tautomerism alters the bondlengths and angles within the TSC moieties of the thione

and thiol tautomers of MAPTSC These structural changescan lead to the tautomers exhibiting different antimicrobialand anticancer potencies The average value of the bondangles 1205791ndash1205795 in the TSCmoieties of all molecules investigatedis 11931∘ implying that the carbon and nitrogen atoms inthese moieties are approximately sp2 hybridized This ascer-tains the occurrence of 120587-conjugation within these moietiesaccounting for their extensive electron delocalization Theaverage value of the bond angles 1205796(S25ndashM29ndashN21) 1205797(N21ndashM29ndashCl31) 1205798(Cl30ndashM29ndashS25) and 1205799(Cl31ndashM29ndashCl30) incomplexes B C and D is 9018∘ which indicates that thesecomplexes adopt a nearly square planar geometry aroundtheir respective central metal ions The values of 1205796ndash1205799 incomplex E suggest a highly distorted tetrahedral geometryaround the central Zn(II) ion The planarity of the TSCmoiety can be judged from the values of the dihedral angles1206011(N21ndashN22ndashC24ndashS25) and 1206013(N21ndashN22ndashC24ndashN26) whichshould normally be 0∘ and 180∘ respectively in a perfectlyplanar TSC moiety From the values of these torsional anglesin Table S3 it can be concluded that the TSC moieties of allmolecules investigated are somewhat planar enhancing 120587-conjugation and electron delocalization

33 Binding Energies and Thermodynamic Parameters forMetal-MAPTSC Interactions The complexes investigated in


Table 2 Binding energies (Δ119864int kcalmol) enthalpies (Δ119867intkcalmol) and Gibbs free energies (Δ119866int kcalmol) of complexformation between A1 and some transition metal chlorides at roomtemperature

Property Transition metal ion [M(II)] present in complexNi2+ Pd2+ Pt2+ Zn2+

Δ119864int minus3523 minus3799 minus4281 minus318Δ119867int minus3583 minus3859 minus4340 minus377Δ119866int minus2100 minus2407 minus2765 722

this study were originally synthesized by refluxing an eth-anolic solution of MAPTSC with ethanolic solutions ofthe corresponding metal salts (NiCl2sdot6H2O PdCl2sdot6H2OPtCl2sdot6H2O and ZnCl2sdot6H2O) [9] In the reaction solutioneach transition metal ion (M2+) would first bind to two Clminusions due to the strong cation-anion electrostatic force ofattraction leading to the formation of the neutral fragmentMCl2 Then MAPTSC coordinates to the transition metalion present in the MCl2 fragment yielding the complexesstudied To determine the coordinating ability or affinityof the thione tautomer of MAPTSC towards the transitionmetal ions studied in ethanol the A1ndashMCl2 binding energies(Δ119864int) enthalpies (Δ119867int) and Gibbs free energies (Δ119866int) atroom temperature were calculated for M = Ni2+ Pd2+ Pt2+and Zn2+ The values of Δ119864int Δ119867int and Δ119866int (tabulated inTable 2) were calculated using

Δ119864int = 119864[M(A1)Cl2] minus (119864A1 + 119864MCl

2

) (1a)

Δ119867int = 119867119900[M(A1)Cl

2] minus (119867

119900A1 + 119867

119900MCl2

) (1b)

Δ119866int = 119866119900[M(A1)Cl

2] minus (119866

119900A1 + 119866

119900MCl2

) (1c)

Here E 119867119900 and 119866119900 respectively represent the thermalenergies enthalpies and Gibbs free energies of the respec-tive species at 29815 K and 100 atm The values of theseparameters were obtained from thermochemical analysis atB3LYP6-31++G(dp)(SDD for metal ions) level of theory

From the computed values of Δ119864int Δ119867int and Δ119866intit is evident that A1 is highly selective towards the metalions studied and the selectivity decreases in the followingorder Pt2+ gt Pd2+ gt Ni2+ gt Zn2+ It is also clear fromthe values in Table 2 that the formation of [Zn(A1)Cl2] inethanolic solution is not thermodynamically feasible at roomtemperature since Δ119866int for A1ndashZnCl2 binding is positiveAlthough Δ119864int and Δ119867int for this process are negative theirnumerical values are very small somewhat confirming thenonfeasibility of A1ndashZnCl2 binding in ethanolic solution at25∘C From the trend shown by the values of Δ119864int Δ119867intand Δ119866int it is clear that the complexation reactions leadingto the formation of the Ni(II) Pd(II) and Pt(II) chloridescomplexes of ligand A1 are thermodynamically feasible inethanolic solution at room temperature Based on theseresults it can be concluded that the thione tautomer ofMAPTSC has a higher affinity for the d8 metal ions Ni(II)

Pd(II) and Pt(II) and can efficiently chelate them in chemicaland biological systems

34 Atomic Charge Analysis Atomic charges are impor-tant parameters in structure-property and structure-activityrelationships affecting dipole moments molecular polariz-abilities acid-base properties and many other molecularproperties [20] Inmetal complexes the interactions betweenthe ligands and the metal ions manifest themselves in thecharges on the ligand moieties and the metal ions [21ndash23]Among the existing atomic charge models we chose naturalpopulation analysis (NPA) [24] and Mullikenrsquos populationanalysis (MPA) [25] for atomic charge calculations on A1and its metal chloride complexes BndashE TheMPAmethod waschosen because it has been the most widely used populationanalysis method for determining atomic charges although itsresults tend to vary with basis set size and yields unnaturalvalues in some cases [13 21 26] The NPA atomic chargemodel was chosen based on the established fact that it isnot basis set dependent and is seemingly the most preferredpopulation analysis method nowadays [26 27] The MPAand NPA atomic charges on selected atoms in A1 andits complexes studied are listed in Table S4 (SupportingInformation) for comparison Significant discrepancies areobserved between the NPA and MPA charges albeit a fewexceptions Since MPA yields unnatural charges in somecases the rest of the discussion pertaining to atomic chargeanalysis is based only on the NPA charges

The transition metal ions in the complexes studied areformally in the second oxidation state but the computednatural charges for these ions (Ni+03321 Pd+02025 Pt+01030and Zn+09438) are considerably lower than +2 signifyingthat they preserve most of the electrons withdrawn fromthe ligandsTherefore ligand-to-metal electron donations areadvantageous over metal-to-ligand back donations in thesecomplexes This charge transfer pattern is corroborated bythe changes undergone by the atomic charges on the liganddonor atoms upon coordination to the central metal ionsThe magnitude of the negative charge on the N21 donoratom of uncomplexedA1 (natural charge is minus02774) reducesslightly in the complexes B C and D (natural charges rangefrom minus02527 to minus02680) but witnesses a modest incrementin complex E (natural charge is minus03440)This shows thatA1-to-metal donation of electrons occurs inBC andD via atomN21 whereas metal-to-A1 back donation of electrons occursin E through N21 In the case of the S25 donor atom of ligandA1 the magnitude of its negative charge in uncomplexed A1(natural charge is minus03681) suffers a drastic reduction in thecomplexes B C and D (natural charges range from +00157to +01030) and a modest reduction in complex E (naturalcharge isminus01977) HenceA1-to-metal charge transfer occursin all complexes studied via atom S25 This charge transferis moderate in complex E and substantial in the complexesB C and D The natural charges on the Cl30 and Cl31ligands are drastically reduced from the formal minus1 charge ona free chloride ion to an average charge minus05535 followingtheir coordination to the central metal ionsThis is indicativeof significant electron donation from Cl30 and Cl31 to the


Table 3 Calculated harmonic vibrational frequencies for ligand A1 and the complexes BndashE at B3LYP6-31++G(dp)(SDD for metal ions)level and the corresponding FT-IR frequencies for BndashD

A1 B C D E Assignment]cal

a ]expb ]cal ]exp ]cal ]exp ]cal ]exp ]cal

3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c

3356 3262 (3247) 3378 3252 3375 3245 3380 3254 3381 ](NndashH)1621 1618 (1588) 1602 1606 1595 1606 1575 1605 1617 ](C=N)1367 1178 1369 1174 1374 1178 1375 1160 1377 ](C=S)mdash mdash 487 mdash 488 mdash 491 mdash 482 ](MndashN)mdash mdash 438 mdash 440 mdash 446 mdash 434 ](MndashS)mdash mdash 351 mdash 333 mdash 328 mdash 295 ](MndashCl)a]cal represents wavenumbers calculated in this workb]exp represents experimental wavenumbers from [9] and those in parentheses from [8]c]119904 represents symmetric stretching vibrations of NndashH bonds in NH2

central metal ions From the foregoing results it is clearthat appreciable metal-to-ligand back donation of electronsonly occurs in complex E This fact is further buttressedby the relatively large positive charge on its central Znion (+09438)

35 Infrared (IR) Vibrational Analysis Molecular vibrationshave attracted much attention from experimental and the-oretical chemists as they are extensively used in chemicalanalysis and in chemical kinetics studies [28] To determinethe mode of coordination of ligand A1 to the transitionmetal ions investigated in this research from a purely IRvibrational point of view the IR spectra of all moleculesstudied have been calculated at B3LYP6-31++G(dp)(SDDfor metal ions) level of theory in gas phase Pertinent theoret-ical IR vibrational frequencies for the molecules investigatedare listed in Table 3 along with their probable assignmentsThe assignments of these vibrational modes have been aidedby the animation option of Gauss View 508 Also listedin Table 3 are the corresponding FT-IR frequencies of themolecules for comparison with the theoretical values Thecalculated frequencies are found to be slightly overestimatedcompared to the experimentally observed values This isattributable to the neglect of anharmonic effects and theuse of isolated molecules in the calculations [22 29] Inorder to improve the agreement between calculated andexperimentally observed IR wavenumbers the calculatedvalues have been scaled down with the scale factor 09614[26 30] To better compare theoretical and experimental IRfrequencies a correlation equation (2) has been establishedbased on the vibrational modes of complexes BndashD Thelarge correlation coefficient (1198772 = 0993) shows a goodlinear agreement between the calculated (scaled) and FT-IR frequencies This ascertains the suitability of the level oftheory employed in these calculations

]cal = 0995]exp minus 9283 (1198772 = 0993) (2)

where ]cal and ]exp represent calculated and experimentalwavenumbers respectively

To determine the coordination mode of ligand A1 basedon vibrational analysis its IR vibrational spectrum has been

compared with those of its metal chloride complexes Thespectra have shown the persistence of two small bandsin the range 3453ndash3356 cmminus1 corresponding to stretchingvibrations of the N22ndashH23 bond and symmetric stretchingvibrations of N26ndashH27 and N26ndashH28 bonds of the aminogroup (NH2)This is indicative of the noncoordination of thenitrogen atoms N22 and N26 to the central metal ions Inthe spectrum of A1 the band at 1621 cmminus1 is assigned to thestretching vibration of the azomethine group (C=N) In thecomplexes this band is shifted towards smaller wavenumbersby 46-4 cmminus1 suggesting the coordination of the azomethinenitrogen N21 to the central metal ionsThe band at 1367 cmminus1in the spectrum of A1 and similar bands in the range 1377ndash1369 cmminus1 in the spectra of the complexes are assigned to thestretching vibration of the C=S group In the complexes thesebands are shifted towards larger wavenumbers by 10-2 cmminus1suggesting the coordination of the thionic sulfur S25 to thecentral metal ions From these results it can be concludedthat A1 acts as a bidentate chelating ligand and coordinatesto the metal ions via the azomethine nitrogen N21 and thethionic sulfur S25 These findings are further supported bythe appearance of new bands in the regions 491ndash482 cmminus1and 446ndash434 cmminus1 due to ](MndashN) and ](MndashS) stretchingvibrations respectively in the complexes

36 Nuclear Magnetic Resonance (NMR) Spectral AnalysisNMR is useful in determining the structure of an organiccompound by revealing the carbon skeleton and the attachedhydrogen atoms [31] Experimentally observed 13C NMRchemical shifts were not found in the literature for thecomplexes currently studied To better describe the carbonskeletons of all investigated molecules their isotropic NMRshielding constants were calculated by the gauge independentatomic orbital (GIAO) method in DMSO as solvent Thecalculations were performed using the B3LYP functionalin conjunction with the pseudopotential LANL2DZ forthe transition metal ions and the Pople style basis set 6-31+G(dp) for the rest of the elements The theoretical 1Hand 13C NMR chemical shifts of the molecules are listedin Table 4 along with the available experimental values for


Table 4 Experimentally observed and calculated 1H and 13C isotropic chemical shifts (with respect to TMS all values in ppm) for A1 andits complexes BndashE The values were calculated at B3LYP6-31+G(dp)(LANL2DZ for metal ions) level of theory in DMSO as solvent by theGIAO method

Atoma A1 B C D E120575cal

b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b

H3 383 378 390 380 393 381 390 383 390H4 384 378 388 380 390 381 388 383 389H5 419 378 421 386 422 386 425 393 423H12 723 739 721 690 728 690 722 680 723H13 749 752 726 690 745 690 746 690 744H14 718 739 724 690 730 690 723 680 727H15 763 752 757 690 762 690 768 690 764H23 880 1010 873 760 890 1000 879 1085 875H27 568 752 602 760 584 780 585 790 590H28 516 752 554 760 546 780 538 790 526C1 5581 5459 5519 mdash 5526 mdash 5496 mdash 5541C6 15857 15961 16005 mdash 15989 mdash 16007 mdash 16029C7 10853 11294 10884 mdash 10918 mdash 10947 mdash 10885C8 12851 12945 12853 mdash 12869 mdash 12864 mdash 12872C9 12344 11294 12186 mdash 12088 mdash 12083 mdash 12101C10 12480 11294 12477 mdash 12453 mdash 12500 mdash 12434C11 11593 11294 11616 mdash 11627 mdash 11601 mdash 11674C16 15571 14721 18129 mdash 17704 mdash 17553 mdash 16716C17 2775 1324 3326 mdash 3407 mdash 3500 mdash 2751C24 17720 17802 17645 mdash 17650 mdash 17637 mdash 17326aFor atomic numbering refer to Figures 1 and 4b120575cal theoretical chemical shifts calculated in this workc120575exp experimentally observed chemical shifts from [8]d120575exp experimentally observed chemical shifts from [9]

comparison The calculated chemical shifts (120575cal) reported inthis tablewere computed relative to those of tetramethylsilane(TMS) using (3) [28 32] In this equation 120575119909abc and 120575TMS

abcrepresent computed absolute isotropic shielding constants ofthe carbon and hydrogen atoms in the molecules studiedand TMS respectively Furthermore 119909 represents any carbonor hydrogen atom in the molecules under investigation Thevalues of 120575119909abc and 120575

TMSabc were calculated at the same level of

theory [B3LYP6-31+G(dp)(LANL2DZ for metal ions)]

120575119909cal = 120575TMSabc minus 120575

119909abc (3)

A good agreement has been found between the calculatedand experimentally observed chemical shifts albeit a fewsignificant discrepancies The chemical shift of a protongenerally varies greatly with its electronic environment Anelectron-withdrawing atom or group decreases shielding andthus moves the chemical shift of an attached or near-byproton towards a higher frequency (low-field) On the otherhand an electron-donating atomor group increases shieldingand moves the chemical shift towards a lower frequency(high-field) [33] For A1 and its complexes the calculated1H NMR chemical shifts of H27 (568ndash602 ppm) and H28(516ndash554 ppm) in the NH2 group and that of H23 (873ndash890 ppm) in NndashH appeared slightly shifted upfield relative

to the corresponding experimental values (752ndash790 ppm forH27H28 and 880ndash1085 ppm forH23)This ismost likely dueto the involvement of these hydrogen atoms in intermolecularhydrogen bonds with the neighboring molecules in theexperimental sample whereas the PCM method did nottake such hydrogen bonds into account during the GIAOcalculations in DMSO H23 is the least shielded proton inall molecules studied due to the electron-withdrawing effectof N22 and to some extent N21 Consequently its theoreticalchemical shift appears downfield in the range 873ndash890 ppmThe calculated 1HNMR signals of the highly shielded protons(H3 H4 and H5) in ndashOCH3 appear in the high-field regionof the NMR spectra in the range 383ndash425 ppm Generallychemical shifts in the range 65ndash85 ppm indicate the presenceof benzene ring protons in a molecule [34] The calculatedchemical shifts of the phenyl protons (H12 H13 H14 andH15) are found in the range 718ndash768 ppm which is in goodagreement with the literature

The calculated 13C NMR spectra have shown that eachinvestigated molecule contains ten carbon atoms in differentelectronic environments Literature survey has shown thatthe 13C chemical shifts of aromatic carbon atoms typicallyoccur in the range 100ndash200 ppm [33] The theoretical 13CNMR chemical shifts of the benzene ring carbons (C6


C7 C8 C9 C10 and C11) in A1 and the complexes arefound in the range 10853ndash16029 ppm which is in excellentagreement with the literature The chemical shifts of thesephenyl carbons are found to increase in the order C7 lt C11lt C9 lt C10 lt C8 lt C6 in each molecule implying thatthe phenyl carbons are in different electronic environmentscreatedmainly by the electron-donating effect of the attachedndashOCH3 group Indeed the ndashOCH3 group is a powerful ortho- para-director [33] and its electron-donating effect is mainlyfelt by the ortho and para carbons

37 Frontier Molecular Orbital Analysis Frontier molecularorbitals (FMOs) which are the highest occupied molecu-lar orbital (HOMO) and the lowest unoccupied molecularorbital (LUMO) are very important quantum chemicalparameters because they play a key role in the electricchemical and optical properties of compounds [28 35]To gain a deeper insight into the nature of the electronictransitions in a molecular species a detailed examination ofits FMOs is crucial owing to their close relationship withelectronic excitation properties [36] To better scrutinize theelectronic absorption spectra of A1 and its complexes BndashE an in-depth qualitative and quantitative analysis of theirpertinent FMOs (those directly participating in the dominantelectronic transitions) has been carried out In order tofacilitate qualitative analysis on these FMOs their electrondensity isosurfaces (shown in Figure 6) were generated withthe aid of the Avogadro 111 [37] graphical user interface Adeeper insight into the nature of the FMOs has been gainedvia a quantitative analysis based on orbital contributions fromdifferent fragments of ligandA1 and its complexesTheorbitalcontributions were calculated using the Hirshfeld method[38] as implemented inMultiwfn 336Thepercentage orbitalcontributions together with the main bond types in each ofthese FMOs are presented in Table 5

It can be seen from the molecular orbital diagrams inFigure 6 that the HOMO and LUMO of ligand A1 aremainly distributed over the TSCmoiety and the benzene ringInspection of Table 5 has shown that the HOMO of A1 issignificantly contributed (4080) by a 119901-type orbital locatedon the sulfur atom S25 designated 119901(S25) An insignificantorbital contribution of 613 to the LUMO of A1 arises fromthe 119901(S25) orbital on the sulfur atom S25 The HOMO isdominated by 120587-bonding molecular orbital characteristicsin addition to the nonbonding characteristic of the 119901-typeorbital on S25 On the other hand the LUMO is dominatedby 120587lowast-antibonding molecular orbital characteristics Orbitalcontributions from the 119901-type orbital on O2 to both theHOMO and LUMO of ligand A1 are minimal

In the case of the metal chloride complexes of A1 theHOMO-2 of B is located mainly on the ligands and isfound to have an orbital contribution of 2374 from 120587-typeorbitals based on A1 and an orbital contribution of 6895from 119901-type orbitals localized on the Cl ligands designated119901(Cl) The HOMO-3 of C resides mainly on the Cl ligands(Cl30 and Cl31) and the Pt(II) ion and is found to have a6413 orbital contribution from 119901(Cl) and a 2411 orbitalcontribution from a 119889-type orbital based on the Pt(II) ion

LUMO of A1 (023 eV) HOMO of A1 (minus737 eV)

LUMO of B (minus174 eV) HOMO minus 2 of B (minus869 eV)

LUMO of C (minus196 eV) HOMO minus 3 of C (minus879 eV)

LUMO + 1 of D (minus075 eV) HOMO of D (minus777 eV)

LUMO of E (minus061 eV) HOMO of E (minus782 eV)

Figure 6 Molecular orbital diagrams for selected HOMOs andLUMOs of the molecules studied calculated at CAM-B3LYP6-31G(dp)(LANL2DZ for metal ions) level of theory in ethanol assolvent

designated 119889(Pt) The HOMO of D is distributed over theentire molecule and has significant orbital contributions of3050 and 5580 from a 119889-type orbital based on the Pd(II)ion designated 119889(Pd) and from 120587-type orbitals located onA1 respectivelyTheHOMOof E is almost entirely composedof 120587-type orbitals on A1 (comprising 9919 120587(A1))

Apparently the electron densities of the LUMOs of B andC are distributed over the entire molecular structures and arefound to benefit from significant metallic orbital contribu-tions of 5954 119889(Ni) and 4924 119889(Pt) respectively Theyalso have orbital contributions from 120587lowast-type orbitals basedon A1 (2241 120587lowast(A1) in B and 2721 120587lowast(A1) in C) as wellas orbital contributions from119901-type orbitals on the Cl ligands(1805 119901(Cl) in B and 2356 119901(Cl) in C) In each of theseLUMOs the 119889-type orbital on the central metal ion has beenfound to interact in an antibonding mode with the 120587lowast orbitalon A1 and the 119901-type orbitals on the Cl ligands The LUMO+ 1 of D is mainly composed of 120587lowast-type orbitals localized onA1 (8078) The LUMO of E is almost entirely dominatedby 120587lowast-type orbitals located on A1 which have contributed9681 of this LUMO


Table 5Molecular orbital compositions in the ground states forA1 and the complexesBndashE calculated by the TD-DFTCAM-B3LYPmethodin DMSO

Molecule Molecular orbital Molecular orbital composition () Main bond typeLigand Index Typea A1b O2 atom S25 atom

A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)

Complexes Index Type M(II)c Ligand A1 Cl ligands

B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)

aL stands for LUMO and H stands for HOMObA1 represents ligand A1 without molecular orbital contributions from atoms O2 and S25cM(II) represents the central metal ion which is Ni(II) for B Pt(II) for C Pd(II) forD and Zn(II) for E

38 Electronic Absorption Spectra The vertical absorptionspectra of the compounds currently investigated were cal-culated based on their optimized ground state geome-tries using the TD-DFT method at the CAM-B3LYP6-31G(dp)(LANL2DZ for metal ions) level of theory Thesecalculations were carried out in two solvents with differentdielectric constants (120576) ethanol with 120576 = 2485 and DMSOwith 120576 = 4683 for comparison TD-DFT is a powerfulmethod that is commonly used nowadays in modeling elec-tronic transitions and excited state geometries of organic andinorganic molecules [39] Its success arises from the remark-able accuracycomputational-time ratio However TD-DFTsignificantly underestimates excitation energies to chargetransfer (CT) or Rydberg states when conventional exchange-correlation functionals are used [40] This is due to the poorasymptotic behavior of conventional exchange-correlationfunctionals in approximations to ground state [41] In orderto partially correct this shortcoming we adopted the range-separated exchange-correlation coulomb-attenuated model(CAM-B3LYP) functional to overcome some of the deficien-cies of B3LYP in dealing with CT excitations [42ndash44]

The calculated vertical excitation energies wavelengthsoscillator strengths (119891) assignments configurational inter-action (CI) coefficients and percentage contributions (P) oftransitions for A1 and complexes BndashE are listed in Table 6along with the experimental transition wavelengths for A1and complexesBndashD for comparison To obtain the nature andenergies of the singlet-singlet vertical electronic transitionsthe first six low-lying excited states have been calculatedGenerally the dominant band in an absorption spectrum cor-responds to the transition with the largest oscillator strength[44] and its wavelength is comparable to the experimental120582max In the current study only the absorption energieswith the greatest oscillator strengths have been consideredThe commonest vertical electronic transitions in organicmolecules are of 120587 rarr 120587lowast or 119899 rarr 120587lowast type whereas in metalcomplexes the involvement of the metal 119889-orbitals leads to

metal-to-ligand charge transfer (MLCT) transitions whichinvolve electronic excitations from mainly metal-based 119889-orbitals to low-lying empty ligand orbitals 119889-119889 transitionswhich occur between partially filled metallic 119889-orbitals andligand-to-metal charge transfer (LMCT) transitions whichoccur from filled ligand based orbitals to partially occupiedmetal 119889-orbitals [45 46] In addition intraligand chargetransfer (ILCT) transitions which involve electronic excita-tions between orbitals based on the same ligand as well asligand-to-ligand charge transfer (LLCT) transitions in whichan electron is moved from one ligand to another may alsooccur in metal complexes

To explore the performance of the computational proce-dure employed in the computation of the electronic absorp-tion spectra we compared calculated and experimentalwavelengths of maximum absorption (120582max) It can be seenfrom Table 6 that the agreement between theoretical andexperimental values of 120582max is excellent with a maximumdiscrepancy of only 25 nm Furthermore we determined thecorrelation between these two sets of data as shown in (4)and an excellent linear relationship was found

120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)

In this equation 120582maxcal and 120582maxexp are calculated andexperimental wavelengths of maximum absorption respec-tively

By inspection of the UV-Vis data in Table 6 for themolecules currently investigated their dominant electronictransitions in ethanol and DMSO as solvents are found tobe very similar in terms of band positions although theirintensities differ slightly The electronic excitation bands forthese molecules are therefore not affected as such by highsolvent polarities On the basis of FMO analysis the peak at257 nm in the absorption spectrum of A1 is assigned to both120587 rarr 120587lowast and 119899 rarr 120587lowast electronic transitions The most intenseabsorption bands in the spectra of B and C are observed at


Table 6 Excitation energies and wavelengths oscillator strengths configuration interaction (CI) coefficients and dominant electronictransitions for A1 and complexes BndashE in different solvents calculated using the TD-DFTCAM-B3LYP method

Solvent Ligand orcomplex

Singletexcited state

Dominantelectronictransition

CIcoefficient(119875 =

2 |CI|2 times 100)

Excitationenergy(eV)

Oscillatorstrength(119891)

Cala 120582max(nm)

Expb 120582max(nm) Assignment

Ethanol

A1 S2 Hrarr L 05550(616) 483 07799 257 260 119899 rarr 120587lowast120587 rarr 120587lowast

B S5 H ndash 2rarr L 05954(709) 349 00325 355 330 LMCT

C S5 H ndash 3rarr L 05381(579) 361 00325 344 340 LMCT

D S5 Hrarr L + 1 06111 (747) 425 04319 291 300 MLCTILCT

E S1 Hrarr L 06668(889) 455 06550 273 mdash ILCT

DMSO




D S5 Hrarr L + 1 06137(753) 426 04864 291 300 MLCTILCT


aCalculated 120582max in this workbExperimental 120582max obtained from [9]

352 and 340 nm and can be attributed to LMCT transitionson the basis of FMO analysis These bands are produced byelectronic transitions from 119901-type orbitals located on the Clligands [119901(Cl)] to 119889-type orbitals on the central metal ions[119889(Ni) and 119889(Pt)] The band at 291 nm in the spectrum ofD arises from the electronic excitation HOMOrarr LUMO +1 Here the HOMO is comprised mainly of 3050 119889(Pd)and 5580 120587(A1) and the LUMO + 1 is almost entirelycomposed of 8078 120587lowast(A1) (see Table 5) Therefore thissignal arises from the electronic transition [119889(Pd) +120587(A1)]rarr[120587lowast(A1)] with amixedMLCT and ILCT character An intenseband at 274 nm is present in the absorption spectrum of Ewith ILCT character solely attributable to 120587 rarr 120587lowast electronictransition between A1-based orbitals

The theoretical absorption spectra for A1 and its com-plexes in DMSO as solvent have been compared graphicallyas shown in Figure 7 It is evidenced in this figure that thevalues of 120582max for the transition metal chloride complexesof A1 are red shifted compared to that of the free ligandThis bathochromic shift of 120582max uponA1-MCl2 complexationcan be attributed to the involvement of low-lying metal-based orbitals in electronic transitions This upper shift of120582max upon transition from A1 to its complexes correspondsto a reduction in maximum excitation energy in the orderA1 gt E gt D gt C gt B indicating that intramolecular chargetransfer (ICT) is more significant in the complexes than inthe free ligand This accounts for the greater lipophilicity ofthese complexes (which controls permeation into the cell and

hence their biological activity) since lipophilicity depends onintramolecular charge delocalization [47]

4 Conclusion

A DFT study on the structural and spectral properties ofMAPTSC and its Ni(II) Pd(II) Pt(II) and Zn(II) chloridecomplexes and on thione-thiol tautomerism of MAPTSC hasbeen carried outwith the aimof deepening the understandingof their structure-activity relationships necessary for rationaldrug design The DFTB3LYP and DFTCAM-B3LYP meth-ods in gas and solvent phases have been employed in thisstudy in conjunction with different basis sets The barrierheights for thione-to-thiol and thiol-to-thione tautomeriza-tion of MAPTSC determined via hydrogen atom migrationstudies in ethanol as solvent are asymp4641 and 3251 kcalmolrespectively These high barrier heights indicate that thione-thiol interconversions of MAPTSC in ethanolic solutionare nearly hindered at room temperature NeverthelessMAPTSC would undergo rapid thione-thiol transformationsin ethanol at higher temperatures Tautomerism analysis hasshown that the thione tautomer of MAPTSC is more stablethan the thiol counterpart in ethanol Therefore MAPTSCcan exist as a mixture of the thione (major) and thiol(minor) tautomers in ethanolic solution at room and highertemperatures Consequently metal complexes of MAPTSCsynthesized in ethanolic solution at temperatures well above

Advances in Chemistry 13O

scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)

Figure 7 Calculated absorption spectra for A1 and complexes BndashEin DMSO

25∘Cwill likely be composed of amixture of thione- and thiol-based complexes

Conformational analysis has revealed five possible con-formers of the thione tautomer of which two are stableenough to be isolated at 25∘C The thione tautomer ofMAPTSC exhibits a higher affinity for the d8 metal ionsNi(II) Pd(II) and Pt(II) as shown by the computed values ofMAPTSC-metal(II) binding energies enthalpies and Gibbsfree energies and can therefore efficiently chelate them inchemical and biological systems Natural population analysishas revealed ligand-metal charge transfer in the MAPTSCcomplexes studied Intramolecular charge transfer (ICT)has been found to be more significant in the complexesthan in uncomplexed MAPTSC accounting for the greaterlipophilicity (which controls permeation into the cell andhence their biological activity) of these complexes A goodagreement has been found between calculated and exper-imentally observed spectral properties (IR UV-Vis andNMR)

Additional Points

Supporting Information The optimized geometries of thetransition states TS1 TS2 TS3 and TS4 are shown inFigure S1 Selected geometric parameters of the thione-thioltautomers of MAPTSC (A1 andA2) along with those of theirtransition metal chloride complexes calculated at B3LYP6-31++G(dp)(SDD formetal ions) level of theory in gas phaseare summarized in Table S3 MPA and NPA atomic chargeson selected atoms of A1 and its metal chloride complexescalculated at B3LYP6-31++G(dp)(SDD formetal ions) levelof theory in ethanol as solvent are listed in Table S4

Competing Interests

The authors declare that there is no conflict of interests re-garding the publication of this paper

Acknowledgments

The authors are sincerely thankful to the IIT Kanpur Indiafor the resources put at their disposal through a CV RamanInternational Fellowship Award (Grant no 101F102) offeredto Julius Numbonui Ghogomu by the Ministry of ExternalAffairs of India and the Federation of Indian Chambers ofCommerce and Industry (FICCI)

References

[1] R Santhakumari K Ramamurthi G Vasuki B M Yamin andG Bhagavannarayana ldquoSynthesis and spectral characterizationof acetophenone thiosemicarbazone a nonlinear optical mate-rialrdquo Spectrochimica ActamdashPart A Molecular and BiomolecularSpectroscopy vol 76 no 3-4 pp 369ndash375 2010

[2] A A Al-Amiery Y K Al-Majedy H Abdulreazak and HAbood ldquoSynthesis characterization theoretical crystal struc-ture and antibacterial activities of some transition metalcomplexes of the thiosemicarbazone (Z)-2-(pyrrolidin-2-yl-idene)hydrazinecarbothioamiderdquo Bioinorganic Chemistry andApplications vol 2011 Article ID 483101 6 pages 2011

[3] M Adams C de Kock P J Smith K Chibale and G SSmith ldquoSynthesis characterization and antiplasmodial evalua-tion of cyclopalladated thiosemicarbazone complexesrdquo Journalof Organometallic Chemistry vol 736 pp 19ndash26 2013

[4] J L BautistaM Flores-Alamo J Tiburcio R Vieto andH Tor-rens ldquoSynthesis and structural characterization of fluorinatedthiosemicarbazonesrdquo Molecules vol 18 no 10 pp 13111ndash131232013

[5] R Harness C Robertson and F Beckford ldquoThiosemicar-bazone complexes of group 12 elements An investigation ofthe thiosemicarbazone from p-dimethylaminobenzaldehyderdquoJournal of Undergraduate Chemistry Research vol 7 no 3 pp92ndash97 2008

[6] S M Kumar K Dhahagani J Rajesh et al ldquoSynthesis char-acterization structural analysis and DNA binding studies ofnickel(II)-triphenylphosphine complex of ONS donor ligandmdashmultisubstituted thiosemicarbazone as highly selective sensorfor fluoride ionrdquo Polyhedron vol 59 pp 58ndash68 2013

[7] G Pelosi ldquoThiosemicarbazonemetal complexes from structureto activityrdquo The Open Crystallography Journal vol 3 no 2 pp16ndash28 2010

[8] H R Fatondji S Kpoviessi F Gbaguidi et al ldquoStructurendashactivity relationship study of thiosemicarbazones on an Africantrypanosome Trypanosoma brucei bruceirdquo Medicinal Chem-istry Research vol 22 no 5 pp 2151ndash2162 2013

[9] R Kothari and B Sharma ldquoSynthesis characterization antibac-terial antifungal antioxidant and dna interaction studies ofthiosemicarbazone transition metal complexesrdquo World Journalof Pharmacy and Pharmaceutical Sciences vol 3 no 7 pp 1067ndash1080 2014

[10] S Stoyanov I Petkov L Antonov T Stoyanova P Karagianni-dis and P Aslanidis ldquoThione-thiol tautomerism and stabilityof 2- and 4-mercaptopyridines and 2-mercaptopyrimidinesrdquo


Canadian Journal of Chemistry vol 68 no 9 pp 1482ndash14891990

[11] Y Xue Y Liu L An et al ldquoElectronic structures and spectraof quinoline chalcones DFT and TDDFT-PCM investigationrdquoComputational and Theoretical Chemistry vol 965 no 1 pp146ndash153 2011

[12] T C Zeyrek ldquoTheoretical study of the N-(25-Methylphen-yl)salicylaldimine schiff base ligand atomic charges molecularelectrostatic potential nonlinear optical (NLO) effects andthermodynamic propertiesrdquo Journal of the Korean ChemicalSociety vol 57 no 4 pp 461ndash471 2013

[13] F Billes A Holmgren and H Mikosch ldquoA combined DFTand vibrational spectroscopy study of the nickel and zinc OO-diethyldithiophosphate complexesrdquo Vibrational Spectroscopyvol 53 no 2 pp 296ndash306 2010

[14] M J Frisch G W Trucks H B Schlegel et al Gaussian 09Revision A02 Gaussian Inc Wallingford Conn USA 2009

[15] R D Dennington II T A Keith and J M Millam Gauss View508 Gaussian Inc Wallingford Conn USA 2009

[16] T Lu and F Chen ldquoMultiwfn a multifunctional wavefunctionanalyzerrdquo Journal of Computational Chemistry vol 33 no 5 pp580ndash592 2012

[17] A D Becke ldquoDensity-functional thermochemistry IIIThe roleof exact exchangerdquoThe Journal of Chemical Physics vol 98 no7 pp 5648ndash5652 1993

[18] W-Y Wang X-F Du N-N Ma S-L Sun and Y-Q QiuldquoTheoretical investigation on switchable second-order nonlin-ear optical (NLO) properties of novel cyclopentadienylcobaltlinear [4]phenylene complexesrdquo Journal of Molecular Modelingvol 19 no 4 pp 1779ndash1787 2013

[19] R N Singh and P Rawat ldquoSpectral analysis structuralelucidation and evaluation of both nonlinear optical prop-erties and chemical reactivity of a newly synthesized ethyl-35-dimethyl-4-[(toluenesulfonyl)-hydrazonomethyl]-1H-pyrrole-2-carboxylate through experimental studies and quantumchemical calculationsrdquo Journal of Molecular Structure vol1054-1055 pp 65ndash75 2013

[20] J G Małecki A Maron M Serda and J Polanski ldquoRuthe-nium(II) carbonyl complexes with thiosemicarbazone ligandsrdquoPolyhedron vol 56 pp 44ndash54 2013

[21] K C Gross P G Seybold and C M Hadad ldquoComparison ofdifferent atomic charge schemes for predicting pKa variationsin substituted anilines and phenolsrdquo International Journal ofQuantum Chemistry vol 90 no 1 pp 445ndash458 2002

[22] M Karnan V Balachandran M Murugan M K Murali andA Nataraj ldquoVibrational (FT-IR and FT-Raman) spectra NBOHOMOndashLUMO molecular electrostatic potential surface andcomputational analysis of 4-(trifluoromethyl)benzylbromiderdquoSpectrochimica Acta Part A Molecular and Biomolecular Spec-troscopy vol 116 pp 84ndash95 2013

[23] Y S Mary P J Jojo C Y Panicker C Van Alsenoy S Ataeiand I Yildiz ldquoTheoretical investigations on the molecularstructure vibrational spectra HOMO-LUMO and NBO anal-ysis of 5-chloro-2-((4-chlorophenoxy)methyl)benzimidazolerdquoSpectrochimica ActamdashPart A vol 122 pp 499ndash511 2014

[24] F Weinhold and C R Landis ldquoNatural bond orbitals andextensions of localized bonding conceptsrdquo Chemistry Educa-tion Research and Practice in Europe vol 2 no 2 pp 91ndash1042001

[25] R S Mulliken ldquoElectronic population analysis on LCAO-MOmolecular wave functions Irdquo The Journal of Chemical Physicsvol 23 no 10 pp 1833ndash1840 1955

[26] Z Demircioglu C A Kastas and O Buyukgungor ldquoThespectroscopic (FT-IR UVndashvis) Fukui function NLO NBONPA and tautomerism effect analysis of (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrilerdquo SpectrochimicaActamdashPart A vol 139 pp 539ndash548 2015

[27] T Lu and S Manzetti ldquoWavefunction and reactivity studyof benzo[a]pyrene diol epoxide and its enantiomeric formsrdquoStructural Chemistry vol 25 no 5 pp 1521ndash1533 2014

[28] A Kumar V Deval P Tandon A Gupta and E DDrsquosilva ldquoExperimental and theoretical (FT-IR FT-RamanUV-Vis NMR) spectroscopic analysis and first-order hyper-polarizability studies of non-linear optical material (2E)-3-[4-(methylsulfanyl) phenyl]-1-(4-nitrophenyl) prop-2-en-1-oneusing density functional theoryrdquo Spectrochimica Acta Part Avol 130 pp 41ndash53 2014

[29] M Karabacak A Coruh and M Kurt ldquoFT-IR FT-RamanNMR spectra and molecular structure investigation of 23-dibromo-N-methylmaleimide a combined experimental andtheoretical studyrdquo Journal of Molecular Structure vol 892 no1ndash3 pp 125ndash131 2008

[30] C J Cramer Essentials of Computational Chemistry Theoriesand Models John Wiley amp Sons West Sussex UK 4th edition2004

[31] A T E Ardjani and S M Mekelleche ldquoTheoretical study of thestructure spectroscopic properties and anti-cancer activity oftetrahydrochromeno[43-b]quinolinesrdquo Journal of Theoreticaland Computational Chemistry vol 14 no 7 Article ID 155005217 pages 2015

[32] S Ramalingam M Karabacak S Periandy N Puviarasanand D Tanuja ldquoSpectroscopic (infrared Raman UV andNMR) analysis gaussian hybrid computational investigation(MEP mapsHOMO and LUMO) on cyclohexanone oximerdquoSpectrochimica Acta Part A Molecular and Biomolecular Spec-troscopy vol 96 pp 207ndash220 2012

[33] K P CVollhardt andN E SchoreOrganic Chemistry Structureand Function W H Freeman and Company New York NYUSA 5th edition 2007

[34] F A CareyOrganic Chemistry James M Smith New York NYUSA 4th edition 2000

[35] R Srivastava and L R Joshi ldquoThe effect of substituted 124-triazole moiety on the emission phosphorescent properties ofthe blue emitting heteroleptic iridium(iii) complexes and theOLED performance A Theoretical Studyrdquo Physical ChemistryChemical Physics vol 16 no 32 pp 17284ndash17294 2014

[36] Y Xue L An Y Zheng et al ldquoStructure and electronic spectralproperty of coumarin-chalcone hybrids a comparative studyusing conventional and long-range corrected hybrid function-alsrdquo Computational andTheoretical Chemistry vol 981 pp 90ndash99 2012

[37] M D Hanwell D E Curtis D C Lonie T Vandermeerschd EZurek and G R Hutchison ldquoAvogadro an advanced semanticchemical editor visualization and analysis platformrdquo Journal ofCheminformatics vol 4 no 8 article 17 2012

[38] T Lu and F W Chen ldquoCalculation of molecular orbital com-positionrdquo Acta Chimica Sinica vol 69 no 20 pp 2393ndash24062011

[39] R Nithya N Santhanamoorthi P Kolandaivel and KSenthilkumar ldquoStructural and spectral properties of 4-bromo-1-naphthyl chalcones AQuantumChemical StudyrdquoThe Journalof Physical Chemistry A vol 115 no 24 pp 6594ndash6602 2011

[40] K Kornobis N Kumar B M Wong et al ldquoElectronicallyexcited states of vitamin B12 benchmark calculations including


time-dependent density functional theory and correlated abinitio methodsrdquo Journal of Physical Chemistry A vol 115 no 7pp 1280ndash1292 2011

[41] X Zarate E Schott D Mac-Leod Carey C Bustos and RArratia-Perez ldquoDFT study on the electronic structure energet-ics and spectral properties of several bis(organohydrazido(2-)) molybdenum complexes containing substituted phosphinesand chloro atoms as ancillary ligandsrdquo Journal of MolecularStructure THEOCHEM vol 957 no 1ndash3 pp 126ndash132 2010

[42] C Adamo and D Jacquemin ldquoThe calculations of excited-stateproperties with time-dependent density functional theoryrdquoChemical Society Reviews vol 42 no 3 pp 845ndash856 2013

[43] H Li Y Li andM Chen ldquoTDDFT studies of electronic spectraand excited states of the triphenylamine-based organic sensitiz-ers and organic sensitizer-titanium dioxide cluster complexesrdquoRSC Advances vol 3 no 30 pp 12133ndash12139 2013

[44] J-P Wang L-K Yan W Guan S-Z Wen and Z-M SuldquoThe structurendashproperty relationship of chiral 111015840-binaphthyl-based polyoxometalates TDDFT studies on the static firsthyperpolarizabilities and the ECD spectrardquo Journal ofMolecularGraphics and Modelling vol 32 pp 1ndash8 2012

[45] T Sivaranjani S Xavier and S Periandy ldquoNMR FT-IR FT-Raman UV spectroscopic HOMO-LUMO and NBO analysisof cumene by quantum computational methodsrdquo Journal ofMolecular Structure vol 1083 pp 39ndash47 2015

[46] C Latouche D Skouteris F Palazzetti and V Barone ldquoTD-DFT Benchmark on inorganic Pt(II) and Ir(III) complexesrdquoJournal of Chemical Theory and Computation vol 11 no 7 pp3281ndash3289 2015

[47] V Chopineaux-Courtois F Reymond G Bouchard P-ACarrupt B Testa and H H Girault ldquoEffects of charge andintramolecular structure on the lipophilicity of nitrophenolsrdquoJournal of the American Chemical Society vol 121 no 8 pp1743ndash1747 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


of MAPTSC currently studied were synthesized at 78∘Cin ethanolic solution [9] a temperature high enough toenhance thione-to-thiol tautomerization of MAPTSC sincethe equilibrium involved is temperature controlled [10]Apparently only the complexes of the thione tautomer werereported to be synthesized and characterized althoughthose of the thiol tautomer might have been formed as wellX-ray diffraction studies which are capable of providingmore insight into the nature of these complexes have notbeen carried out till date Moreover an in-depth analysisof the experimentally determined spectral data for thesemolecules has not yet been performed To address theseissues quantum chemical calculations are more appropriateand elegant compared to experimental methods Theresults obtained from such calculations are commonly usednowadays to investigate the relationship between electronicstructure and spectral properties [11] We have pursuedtheoretical studies on these molecules in order to providedetailed information on their structures properties andrelative stability of the thione-thiol tautomers of MAPTSCall of which is essential for better understanding of theirstructure-activity relationships as well as their reactivityin chemical and biological systems In this regard thecurrent study is aimed at providing a detailed analysis of thestructural and spectral properties of MAPTSC along withsome of its transition metal chloride complexes in a bidto facilitate rational drug design using these molecules asprecursors

In this work we set out mainly to theoretically optimizethe geometries of the thione and thiol tautomers ofMAPTSCdetermine their relative stability and possible conformersinvestigate their metal-coordinating abilities and perform adetailed structural and spectral analyses of the tautomersalong with their Ni(II) Pd(II) Pt(II) and Zn(II) chloridecomplexes In a strict sense we have calculated and analyzedthe geometric parameters (bond lengths bond angles anddihedral angles) atomic charge distribution IR vibrationalmodes NMR chemical shifts and electronic absorptionspectra of thesemolecules FurthermoreMAPTSC-metal(II)binding energies enthalpies and Gibbs free energies as wellas thermodynamic parameters associated with thione-thioltautomerism and rotational isomerism of MAPTSC havebeen studied To determine the suitability of our theoreticalapproaches relevant experimental data has been comparedwith our theoretical results The density functional theory(DFT) method has been chosen for this study because itis faster and less computationally intensive takes betteraccount of electron correlation and has a precise accuracyin reproducing experimental data [12] In addition the DFThas been proven to be a very reliable method for transitionmetal complexes [13] and is generally considered to be a goodcompromise between accuracy and computational time

2 Computational Details

All quantum chemical calculations were performed withthe Gaussian 09W computational package [14] The pre-and postprocessing of data were carried out with Gauss

View 508 [15] and Multiwfn 336 [16] The ground stategeometries of the molecules studied were optimized withoutconstraints of any sort using the Beckersquos three-parameterLee-Yang-Parr (B3LYP) DFT functional [17] This functionalwas chosen because it produces relatively good geometriesof transition metal-containing molecular systems [18] Whilethe geometries of the thione-thiol tautomers and conformersofMAPTSCwere fully optimized at the B3LYP6-31++G(dp)level of theory those of the transition metal chloride com-plexes of the thione tautomer of MAPTSC were optimized atthe B3LYP6-31++G(dp)(SDD for metal ions) level of the-ory Here SDD stands for the small core Stuttgart-Dresdeneffective core potential which reduces computational costand includes some relativistic effects in the calculations Toconfirm the fully optimized geometries of the moleculesas local minima on their potential energy surfaces (PES)harmonic vibrational frequencies were computed at the samelevel of theory as that used for geometry optimizationNo imaginary frequencies were obtained for any of theoptimized geometries ascertaining that they are minima ontheir respective PES The restricted closed-shell Kohn-Shammodel was adopted for all theoretical calculations reportedin this paper since all molecules studied are closed-shellsystems

The effects of the bulk solvent environment on geom-etry configurations and absorption spectra were taken intoaccount by means of the polarizable continuum model(PCM) using the integral equation formalism approach (IEF-PCM) Time-dependent density functional theory (TD-DFT)calculations at the CAM-B3LYP6-31G(dp)(LANL2DZ formetal ions) level of theory were performed in order to simu-late the UV-Vis spectra of the molecules under investigationHere the effective core potential LANL2DZ was preferredover SDD for the metal ions because LANL2DZ resulted insignificant speed-ups of the TD-DFT calculations but yieldedresults that agreed remarkably with experimental valuesMoreover negligible discrepancies were observed betweenthe results obtained by employing LANL2DZ for the metalions and those obtained by using SDD for these metal ionsin the complexes currently studied Isotropic NMR shieldingconstants were calculated by the gauge independent atomicorbital (GIAO) method

3 Results and Discussion

31 Molecular Geometry of MAPTSC Before computing themolecular properties of metal complexes it is necessary toanalyze the molecular structures of the ligands in orderto identify their stable tautomers and conformers In thisregard we have carried out tautomerism and conformationalanalyses on MAPTSC

311 Hydrogen Atom Migration Studies and TautomerismAnalysis on MAPTSC Thione-to-thiol tautomerism ofMAPTSC in ethanol (elucidated in Figure 1) was simulatedvia hydrogen atom migration studies During the processH23 migrates from the hydrazinic nitrogen (N22) to thethionic sulfur (S25) In Figure 1 A1 and A2 represent the





A1Conformer II

A1Conformer I

A2

TS0

minus102658

minus102656

minus102654

minus102652

minus102650

minus102648

Ener

gy (H

artre

e)


EA = 4641kcalmol

EA = 3251kcalmol














Ener

gy (H

artre

e)

minus1026545

minus1026550

minus1026555

minus1026560

minus1026565

minus1026570

minus1026575

minus1026580

TS1TS2

TS3 TS4

II

II

III IV V

minus50 0 50 100 150 200 250 300 350 400














(B) (C)

(E)(D)












2

) (1a)

Δ119867int = 119867119900[M(A1)Cl

2] minus (119867

119900A1 + 119867

119900MCl2

) (1b)

Δ119866int = 119866119900[M(A1)Cl

2] minus (119866

119900A1 + 119866

119900MCl2

) (1c)










3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c




]cal = 0995]exp minus 9283 (1198772 = 0993) (2)








b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





A1Conformer II

A1Conformer I

A2

TS0

minus102658

minus102656

minus102654

minus102652

minus102650

minus102648

Ener

gy (H

artre

e)


EA = 4641kcalmol

EA = 3251kcalmol














Ener

gy (H

artre

e)

minus1026545

minus1026550

minus1026555

minus1026560

minus1026565

minus1026570

minus1026575

minus1026580

TS1TS2

TS3 TS4

II

II

III IV V

minus50 0 50 100 150 200 250 300 350 400














(B) (C)

(E)(D)












2

) (1a)

Δ119867int = 119867119900[M(A1)Cl

2] minus (119867

119900A1 + 119867

119900MCl2

) (1b)

Δ119866int = 119866119900[M(A1)Cl

2] minus (119866

119900A1 + 119866

119900MCl2

) (1c)










3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c




]cal = 0995]exp minus 9283 (1198772 = 0993) (2)








b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





Ener

gy (H

artre

e)

minus1026545

minus1026550

minus1026555

minus1026560

minus1026565

minus1026570

minus1026575

minus1026580

TS1TS2

TS3 TS4

II

II

III IV V

minus50 0 50 100 150 200 250 300 350 400














(B) (C)

(E)(D)












2

) (1a)

Δ119867int = 119867119900[M(A1)Cl

2] minus (119867

119900A1 + 119867

119900MCl2

) (1b)

Δ119866int = 119866119900[M(A1)Cl

2] minus (119866

119900A1 + 119866

119900MCl2

) (1c)










3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c




]cal = 0995]exp minus 9283 (1198772 = 0993) (2)








b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










(B) (C)

(E)(D)












2

) (1a)

Δ119867int = 119867119900[M(A1)Cl

2] minus (119867

119900A1 + 119867

119900MCl2

) (1b)

Δ119866int = 119866119900[M(A1)Cl

2] minus (119866

119900A1 + 119866

119900MCl2

) (1c)










3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c




]cal = 0995]exp minus 9283 (1198772 = 0993) (2)








b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







2

) (1a)

Δ119867int = 119867119900[M(A1)Cl

2] minus (119867

119900A1 + 119867

119900MCl2

) (1b)

Δ119866int = 119866119900[M(A1)Cl

2] minus (119866

119900A1 + 119866

119900MCl2

) (1c)










3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c




]cal = 0995]exp minus 9283 (1198772 = 0993) (2)








b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





3415 3373 (3400) 3449 3346 3453 3347 3451 3350 3452 ]119904(NH2)c




]cal = 0995]exp minus 9283 (1198772 = 0993) (2)








b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




b 120575expc 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b 120575expd 120575cal

b






120575119909cal = 120575TMSabc minus 120575

119909abc (3)




















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

















A1 60 L 9170 217 613 120587lowast(A1)59 H 5277 643 4080 120587(A1) + 119901(S25)


B 86 L 5954 2241 1805 119889(Ni)83 H minus 2 731 2374 6895 119901(Cl)

C 86 L 4924 2721 2356 119889(Pt)82 H minus 3 2411 1175 6413 119901(Cl)

D 87 L + 1 1335 8078 586 120587lowast(A1)85 H 3050 5580 1370 119889(Pd) + 120587(A1)

E 83 L 270 9681 049 120587lowast(A1)82 H 033 9919 048 120587(A1)






120582maxcal = 0756120582maxexp + 7161 (1198772 = 0931) (4)









2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







2 |CI|2 times 100)



Cala 120582max(nm)


Ethanol






DMSO










4 Conclusion



scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


scill

ator

stre

ngth

(au

)

09

08

07

06

05

04

03

02

01

00

Wavelength (nm)150 175 200 225 250 275 300 325 350 375 400 425 450

A1BC

DE

120582max = 257nm(482 eV)

120582max = 274nm(453 eV)

120582max = 291nm(426 eV)

120582max = 340nm(365 eV)

120582max = 352nm(352 eV)




Additional Points


Competing Interests


Acknowledgments


References





























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article A DFT Study of Some Structural and...

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