Ss

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Optik 125 (2014) 1390– 1395

Contents lists available at ScienceDirect

Optik

j o ur nal hom epage: www.elsev ier .de / i j leo

ynthesis, crystal growth, spectral, optical, thermal and dielectrictudies of dichloro(4-hydroxy-l-proline)cadmium(II) single crystals

. Mohana Priyadarshinia, A. Chandramohana,∗, G. Anandha Babub, P. Ramasamyb

Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore 641020, Tamilnadu, IndiaCentre for Crystal Growth, SSN College of Engineering, SSN Nagar 603110, Tamilnadu, India

r t i c l e i n f o

rticle history:eceived 12 March 2013ccepted 25 August 2013

eywords:rystal growthharacterization techniques

a b s t r a c t

A semi-organic nonlinear optical material dichloro(4-hydroxy-l-proline)cadmium(II) (DCHPC) of molec-ular formula [CdCl2(C5H9NO3)] has been successfully synthesized and good optical quality single crystalswere grown by slow solvent evaporation solution growth technique at room temperature. The presenceof the elements in the grown crystal has been confirmed by Energy dispersive spectrometry (EDS) andCHN analyses. The 1H and 13C NMR spectra were recorded to confirm the molecular structure of DCHPCcrystal. The single crystal XRD analysis indicated that the crystal belongs to monoclinic structure withlattice parameters a = 8.154(2) A, b = 7.223(4) A, c = 7.697(3) A and space group P21. The optical transmis-

olution growth-ray diffractiononlinear optical materials

sion window of the DCHPC has been identified by UV–vis–NIR studies. The presence of various functionalgroups in the crystal was confirmed by FT-IR spectral analysis. The second harmonic generation (SHG)efficiency was estimated using the modified Kurtz–Perry powder test and was found to be 0.5 times thatof KDP. The fluorescence emission spectrum of the title crystal shows blue emission. The TG/DTA studywas carried out to determine the thermal stability of the grown crystal. Dielectric property was studiedat various frequencies.

. Introduction

Amino acids are the building blocks of proteins that are consid-red to be the very important for most of the processes in livingrganisms [1] and their complexes belong to a class of organicaterials find immense nonlinear optical (NLO) applications [2].

he presence of acidic carboxyl and basic amino group paves theay for the formation of zwitter ion or dipolar ion as a result of

nternal neutralization reaction. This dipolar nature of amino acidselps to improve the crystal’s hardness [3] and the physical andhemical properties also making them as a peculiar candidates inonlinear optical field [4]. The organic materials have excellentroperties compared to the conventional inorganic solids whichhow ultrafast response times, lower dielectric constants, betterrocessability characteristics and enhanced NLO responses [5]. Buthe practical applications of the organic nonlinear optical materi-ls are limited because of their poor physicochemical stability andow mechanical strength [6]. For overcoming the above difficulties

f the organic NLO crystals, in recent years the organic materialsere mixed with inorganic materials to improve their chemical

tability, physico-chemical properties, mechanical strength and

∗ Corresponding author. Tel.: +91 9994283655; fax: +91 0422 2693812.E-mail address: dracmsrmv20@gmail.com (A. Chandramohan).

030-4026/$ – see front matter © 2013 Elsevier GmbH. All rights reserved.ttp://dx.doi.org/10.1016/j.ijleo.2013.08.008

© 2013 Elsevier GmbH. All rights reserved.

nonlinear optical coefficients, which are the important parame-ters for an NLO crystal [7,8]. According to Dewar–Chatt–Duncansonmodel, the binding between metal and ligand is due to theinterplay of donor and acceptor contributions [9]. Yukawa et al.[10] have already reported the structure of dichloro(4-hydroxy-l-proline)cadmium(II) and it belongs to monoclinic crystal systemwith P21 space group. In the present work we report synthesis,crystal growth, spectral, optical, thermal and dielectric propertiesof metal coordinated complex of DCHPC.

2. Experimental

2.1. Synthesis, crystal growth and elemental confirmation

The title complex crystal was grown from an aqueous solutionemploying the slow solvent evaporation solution growth techniqueat room temperature. The chemicals used for synthesis are of ana-lytical grade and are commercially available. Equimolar solutionsof 4-hydroxy-l-proline and cadmium chloride hemipenta hydratewere prepared separately in millipore water and henceforth mixedtogether. The solution was stirred well for several hours on a water

bath maintained at 60 ◦C. Then the solution was filtered througha quantitative whatmann 41 grade filter paper and kept aside in aroom conducive for growth of single crystals. Clear colorless crys-tals were obtained after 20 days. The crystals were dried in vacuum

K. Mohana Priyadarshini et al. / Optik 125 (2014) 1390– 1395 1391

Fig. 1. Photograph of as-grown crystals of DCHPC.

Table 1CHN analysis data of DCHPC.

Element % Present report Theoretical Reported [10] Reported [11]

C 18.56 19.09 19.08 18.98

agini

2

CTtlD

sFgectp

Table 2EDS data of DCHPC.

Element wt% at%

H 2.93 2.89 2.86 3.01N 4.46 4.45 4.49 4.44

t 50 ◦C for several hours. Well-defined colorless single crystals ofood transparency were collected. The grown crystals are shownn Fig. 1. The 4-hydroxy-l-proline molecule has two groups (a gua-adyl and amino) that can be protonated. The reaction takes place

n accordance with the following equation.

C5H9NO3 + 2CdCl2·2.5H2O → 2[CdCl2(C5H9NO3)] + 5H2O

The CHN analysis of DCHPC was performed using VarioEL IIIHNS Elemental analyzer. The corresponding data are given inable 1. The data show good agreement between the experimen-ally determined and theoretically calculated values within theimits of permissible error. The result confirms the formation ofCHPC complex.

The energy dispersive spectrometry was employed to find thetoichiometric composition which was done using INCA pentaETX3 scanning electron microscope. In this investigation therown crystal was subjected to EDS analysis to confirm the pres-nce of elemental compositions. The presence of chlorine andadmium elements in the grown crystal is confirmed by EDS and

he spectrum is shown in Fig. 2. The elements, wt% and at% areresented in Table 2.

Fig. 2. EDS spectrum of DCHPC.

Cl 13.81 6.92Cd 18.90 2.99

2.2. Characterization techniques

The grown DCHPC crystal was subjected to various character-ization techniques like 1H and 13C NMR spectral analyses, singlecrystal X-ray diffraction, Fourier transform infrared (FT IR), UV–visspectral analysis, thermal analyses, fluorescence emission and non-linear optical studies. Single crystal X-ray diffraction (XRD) studieshave been carried out using ‘ENRAF (BRUKER)NONIUS CAD4’diffractometer with graphite monochromated Mo K� radiation(� = 0.71073 A) to determine the cell parameters. The optical trans-mission spectrum of DCHPC crystals has been recorded in the region200–1100 nm using a Shimadzu UV-1061 UV–vis spectrophotome-ter in solution using water as a solvent. The coordination of4-hydroxy-l-proline with cadmium chloride was confirmed by FTIR studies using SHIMADZU model IR Affinity-1 spectrometer in therange 4000–400 cm−1 following the KBr pellet technique. The 1Hand 13C NMR spectra were recorded using the ‘BRUKER AVANCEIII’ 500 MHz (AV 500) spectrometer with TMS as the internal refer-ence standard and D2O as the solvent. The fluorescence emissionspectrum of DCHPC was recorded using HORIBA JASCO V-670 Fluo-rolog 3 spectrofluorometer. The TGA and DTA traces of the samplewere taken using STA 409 PL LUXX with a heating rate of 10 K/minin nitrogen atmosphere. The NLO property of DCHPC was tested byKurtz and Perry powder SHG technique using a Q-switched Nd:YAGlaser (1064 nm) and KDP was taken as the reference material. Singlecrystal of DCHPC with polished surface was taken for the mea-surements of dielectric constant and dielectric loss by using theHIOKI 3532-5D LCR HITESTER instrument in the frequency range50 Hz to 5 MHz. The detailed results are presented in the proceedingsections.

3. Results and discussion

3.1. 1H and 13C nuclear magnetic resonance spectral analyses

The recorded 1H NMR Spectrum of the title crystal is depictedin Fig. 3. The appearance of six distinct proton signals in the spec-trum confirms the presence of six different proton environments

in the title crystal. The signal at 4.7 ppm is assigned to solvent D2O.The hydroxy proton exhibits a singlet signal at 4.6 ppm. The tripletsignal centered at 4.31 ppm is attributed to the C2 methine pro-ton. The splitting of the signal in to triplet is due to coupling of

Fig. 3. 1H NMR spectrum of DCHPC.

1392 K. Mohana Priyadarshini et al. / Optik 125 (2014) 1390– 1395

Fig. 4. 13C NMR spectrum of DCHPC.

mssoTpmtsqCep

atstarp

3

autpn

TS

Fig. 5. FT IR spectrum of DCHPC.

ethylene protons in the neighborhood. The doublet of doubletignal centered at 3.39 ppm owes to the C3 methylene proton. Theplitting of signal as a doublet of doublet indicates the influencesf the C2 and C4 methine protons on the C3 methylene proton.he doublet (multiplet) at 2.36 ppm is assigned to C5 methyleneroton. This appears as a doublet due to the coupling with C4ethine proton. The signal due to C4 methine proton appears in

he upfield regions as a quintet centered at 2.12 ppm. This upfieldhift is due to the presence of hydroxy group. This appears as auintet due to the coupling of C4 methine proton with the nearest3 and C5 methylene protons. The +NH2 protons of the same moi-ty remain submerged in the signals of methylene and methinerotons.

The 13C NMR spectrum of the title crystal is shown in Fig. 4. Theppearance of four signals in the aliphatic region of 13C NMR spec-rum confirms with greater degree of precision of the moleculartructure of the title crystal. The weak signal at 174.42 ppm oweso the carboxylic carbon of 4-hydroxyprolinium moiety. The peaksppearing at 70.07, 59.83, 53.09 and 37.38 ppm have been assigned,espectively, to C2, C5, C4 and C3 carbon atoms in 4-hydroxy-l-rolinium moiety in the complex.

.2. Single crystal X-ray diffraction studies

Single crystal X-ray diffraction study was carried out on thes-grown DCHPC single crystal. From Table 3 it is seen that thenit cell parameters derived are in very good agreement withhe corresponding reported values [10]. Dichloro(4-hydroxy-l-roline)cadmium(II) crystal belongs to monoclinic system withoncentro symmetric space group P21. The chemical structure of

able 3ingle crystal XRD data of DCHPC.

Lattice parameters

Present work Reported [10]

a = 8.154(2) A a = 8.196 (4) Ab = 7.223(4) A b = 7.275 (3) Ac = 7.697(3) A c = 7.740(4) Aˇ = 103.65(3)◦

= 103.73(4)◦

V = 441.0(2) A3 V = 448.3(4) A3

DCHPC crystal is given below

Cd

Cd

Cl

Cl

Cl

ClCl

Cl

O

O

O

O

O

O

C

C

C

HC

CH

HC

NH2CH2CH

CH2OH

H2N

H2N

H2C

H2C

H2C

H2C HC

HC

HO

HO

3.3. Fourier transform infrared (FT-IR) spectral analysis

The FT IR spectrum of DCHPC recorded in the range4000–400 cm−1 and is shown in Fig. 5. It is evident from the spec-trum that the small intense band at 3286 cm−1 is assigned to theOH stretching vibration. The bands at 3136 and 3039 cm−1 dueto N+ H asymmetric and symmetric stretching vibrations respec-tively. The C H asymmetric and symmetric stretching vibrations ofthe methylene group are observed at 2951 and 2924 cm−1, respec-tively. The absorption bands in the region 2735–2457 cm−1 are dueto the superimposed O H and +NH2 stretching vibrations. Rata-jczak et al. [12] determined that the lack of any strong IR band at1700 cm−1 clearly indicates the existence of the COO− ion in zwitterionic form. The band at 1639 cm−1 is due to NH2

+ in-plane defor-mation. The bands at 1577 and 1400 cm−1 are assigned to COO−

asymmetric and symmetric stretching vibrations respectively. Theband at 1323 cm−1 owes to the OH in-plane bending vibration. Astrong band at 1257 cm−1 corresponds to the C O stretching fre-quency. The less intense band at 1222 cm−1 and the sharp band at1087 cm−1 are due to the C N asymmetric and symmetric stretch-ing vibrations. The characteristic IR bands for different molecular

groups present in DCHPC complex molecule have been identifiedand their assignments are given in Table 4.

K. Mohana Priyadarshini et al. / Optik 125 (2014) 1390– 1395 1393

Table 4FT IR band assignments of DCHPC single crystals.

Wave number (cm−1) Assignments

3286 OH stretching3136 N+ H asymmetric stretching3039 N+ H symmetric stretching2951 C H asymmetric stretching2924 C H symmetric stretching2735, 2600, 2503 and 2457 Superimposed OH and +NH2 stretching1639 +NH2 in-plane deformation1597 N H asymmetric deformation1577 COO− asymmetric stretching1400 COO− symmetric stretching1323 OH in-plane bending1257 C O stretching1222 C N asymmetric stretching1087 C N symmetric stretching960 OH out of plane bending844 C C N stretching756 C C skeletal stretching

3

rlrpmdpcam

3

doscidssF

Fig. 7. The fluorescence emission spectrum of DCHPC.

613 COO− wagging462 and 420 COO− rocking

.4. UV–vis–NIR transmission studies

The Transmission spectrum of the grown DCHPC crystal wasecorded in the wavelength range 200–1100 nm. It was corre-ated with 4-hydroxy-l-proline ligand transmission spectrum. Theecorded transmission spectrum is depicted in Fig. 6. The attainedercentage of transmission is 91% in the visible region. The trans-ittance decreases rapidly around 200 and 264 nm, which may be

ue to n→�* or ligand–metal charge transfer transition in the com-lex. The good transmittance in the visible and NIR regions of therystal is due to the absence of strongly conjugated bonds in themino acid (4-hydroxy-l-proline) [3] and also the filled d10 shell ofetal ion in the complex [13].

.5. Nonlinear optical studies

The second harmonic generation (SHG) efficiency of DCHPC wasetermined by a modified version of the powder technique devel-ped by Kurtz and Perry [14]. The uniform particle size of the growningle crystal of DCHPC was powdered and then packed in a one sidelosed micro capillary tube and exposed to laser radiations with thenput beam energy of 2.5 mJ/p. The SHG output (532 nm) is finallyetected by a photomultiplier tube and displayed on the oscillo-

cope. The emission of green light confirms the generation of theecond harmonics. The output power was measured to be 8.7 mV.or the same input, KDP emitted the green light with the output

Fig. 6. UV–vis–NIR transmission spectrum of DCHPC.

Fig. 8. TG/DTA spectra of DCHPC.

power of 18 mV. Second harmonic generation (SHG) efficiency wasfound to be 0.5 times that the value of KDP.

3.6. Fluorescence studies

The emission of light which ceases after the cause of excitationin cut off is known as fluorescence and this is generally observedin those organic molecules which have rigid framework and notmany loosely coupled substituent through which vibronic energycan flow out [15]. The fluorescence emission spectrum was mea-sured in the range 375–825 nm and is depicted in Fig. 7. A peak at470 nm was observed in the emission spectrum. The results indi-cate that DCHPC crystals have a blue fluorescence emission.

3.7. Thermal analyses

The TG/DTA thermograms of the DCHPC crystal are shown inFig. 8. The TGA thermogram shows that the decomposition ofthe complex compound takes place in two stages when the com-pound is heated from room temperature to 500 ◦C. The first stagedecomposition commences at 250 ◦C with the elimination of amolecule each of CO2 and H2O which is due to dehydration anddecarboxylation of the ligand, respectively. On further heating thecompound incurs yet another weight loss between 329 and 498 ◦Cwith evolution of H2 and NH3 molecules. The decomposition pat-

tern formulated for the weight loss matches well with the observedweight losses (Table 5). The following equations show the decom-position pattern of DCHPC complex crystal. The remaining residualmass 73.91% which may be due to the presence of residual carbon

Table 5Percentage weight loss of DCHPC crystal in TGA thermogram.

Stage Experimental (%) Theoretical (%)

1 60.65 622 21.38 21

1394 K. Mohana Priyadarshini et al. / Optik 125 (2014) 1390– 1395

F

m5

(

C

Famned

3

tdfcc

ε

wεvtrwaaaft

tlTslo

[

ig. 9. Variation of dielectric constant with frequency of the applied electric field.

ass and cadmium chloride, since CdCl2 boils at temperature above00 ◦C.

Stage 1C5H9NO3)CdCl2

314.44

�−→250−329 ◦C

C4H7NCdCl2252.44

+ CO244

↑ +H2O18

↑19.72% weight loss

Stage 2

4H7NCdCl2252.44

�−→329−498 ◦C

CdCl2 + NH317

↑ +2H24

↑ +4C

6.68% weight loss

rom the DTA thermogram (Fig. 8), it is observed that there is sharp endothermic peak at 255 ◦C, which corresponds to theelting point of the compound. Further, it indicates that there is

o phase transition before melting. This is followed by a broadndotherm starting at 343.9 ◦C, which corresponds to the secondecomposition temperature of DCHPC.

.8. Dielectric studies

A study of dielectric response in crystals is one of the basic elec-rical properties which give the information about the electric fieldistribution within the solid. The silver coating on the oppositeaces of the polished sample crystal was placed between the twoopper electrodes to form a parallel plate capacitor. The dielectriconstant (εr) is calculated using the relation

r = Cd

ε0A

here C is the capacitance, d is the thickness, A is the area and0 is the absolute permittivity of the free space. Fig. 9 shows theariations of dielectric constant with applied frequency at roomemperature. It is seen from the plot that the dielectric constant iselatively high in the lower frequency region and then decreasesith the applied frequency. The high values of dielectric constant

t low frequencies may be due to the presence of combinations ofll four polarizations namely space charge, orientation, electronicnd ionic polarization. The low value of dielectric constant at highrequencies occurs due to the loss of these polarizations at lowemperature [16].

The dielectric loss studied as a function of frequency at roomemperature is shown in Fig. 10. These curves suggest that dielectricoss is also strongly dependent on the frequency of the applied field.

he higher values of dielectric loss at low frequencies originate frompace charge polarization mechanism dipoles. The characteristic ofow dielectric loss at high frequencies classifies that the enhancedptical quality nature of the grown sample with lesser defects [17].

[

Fig. 10. Variation of dielectric loss with frequency of the applied electric field.

4. Conclusion

The metal organic coordination complex of dichloro(4-hydroxy-l-proline)cadmium(II) (DCHPC) synthesized and single crystals ofit were grown by slow solvent evaporation solution growth tech-nique method at room temperature. Elemental analysis confirmsthe formation of DCHPC complex. The NMR spectral and EDS anal-ysis confirms the molecular structure of DCHPC. Single crystalX-ray diffraction study revealed that the DCHPC crystal belongs tomonoclinic system with noncentro symmetric space group P21. TheUV–vis transmission spectrum of DCHPC showed that the crystalis transparent in the range 400–1100 nm. The presence of vari-ous functional groups in DCHPC crystal and protonation of thecyclic secondary nitrogen in the ligand were confirmed by Fouriertransform infrared spectroscopic study. The fluorescence emissionanalysis confirms the blue emission from the DCHPC complex. Ther-mal analyses show that the title crystal possesses high thermalstability. Its SHG efficiency was found to be 0.5 times that the valueof KDP. The dielectric studies reveal the low dielectric constant anddielectric loss of the crystal at high frequency region. Owing to allthese properties DCHPC crystal may be a good candidate for variousoptical applications.

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