STUDIES ON THE METAL COMPLEXES OF FIRST

AND SECOND TRANSITION SERIES

A

THESIS SUBMITTED

BY

VANDANA PANDEY (Regn. No. 2K05-NITK-1075)

FOR THE AWARD OF DEGREE OF

DOCTOR OF PHILOSOPHY

IN

CHEMISTRY

UNDER THE SUPERVISION OF

Dr. DINESH KUMAR

DEPARTMENT OF CHEMISTRY

NATIONAL INSTITUTE OF TECHNOLOGY

KURUKSHETRA-136119

HARYANA, INDIA

2011

CONTENTS Foreword i- iv

INTRODUCTION 1-116

Chapter 1 Coordination compounds of Schiff base containing urea moiety

117-124

Chapter 2

Ligational behavior of the azetidin-2-one derived from

salicylaldehyde and o-hydroxyphenylurea towards some di-, tri- and hexavalent metal ions

125-129

Chapter 3 Physico-chemical studies on the coordination compounds of thiazolidin-4-one derived from salicylaldehyde and o-hydroxyphenylurea

130-135

Chapter 4 Studies on the coordination compounds of the polystyrene-anchored Schiff base obtained from the condensation of chloromethylated polystyrene, 3-formylsalicylic acid and o-

hydroxyphenylurea

136-141

Appendix-1 Abbreviations 142-143

Appendix-2 Materials and sources 144-145

Appendix-3 Analyses and physical measurements 146-147

Appendix-4

Tables at a glance 148-156

Appendix-5 Figures at a glance

157-196

References 197-215

Summary 216-217

Future scope 218-218

List of published papers and their reprints

i

FOREWORD The Thesis contains General Introduction, four Chapters dealing with the syntheses, elemental analyses, spectral studies and the magnetic susceptibility measurements on the coordination compounds of Schiff base, azetidin-2-one, thiazolidin-4-one, polystyrene-anchored Schiff base. The organization of the Thesis is such that each

Chapter consists of Abstract, Introduction, Experimental, Results and Discussion and Conclusion. The Appendicies 1, 2, 3, 4 and 5 have been used for the Abbreviations for the chemical entities, Materials and sources, Analyses and physical measurements, Tables and Figures respectively used elsewhere. The Synopsis of each Chapter is presented below:

Chapter 1 This Chapter describes the syntheses and characterization of the Schiff base, LH3 (1) derived from the condensation of salicylaldehyde and o-hydroxyphenylurea and its coordination compounds with Zn(II), Co(II), Ni(II), Fe(III) and Zr(OH)2(IV) ions. The nucleophilic addition reaction followed by the elimination of one H2O molecule between salicylaldehyde and o-hydroxyphenylurea in equimolar ratio in MeOH results in the formation of 1. A MeOH solution of the latter reacts with a MeOH solution of Zn(II), Co(II), Ni(II), Fe(III) and Zr(OH)2(IV) ions in equimolar ratio and forms [Zn(LH)(MeOH)] (2), [M(LH)(MeOH)2]2 (3, M = Co, Ni), [FeCl(LH)(MeOH)]2 (4) and [Zr(OH)2(LH)(MeOH)2] (5) respectively. The coordination compounds are insoluble in H2O, MeOH and EtOH but soluble in DMF and DMSO. They have been characterized on the basis of elemental analyses, molecular weight, spectral (IR, reflectance, 1H NMR) studies, thermo-gravimetric analyses and the magnetic susceptibility measurements. Their

molar conductance values (M = 4.58.2 mho cm2 mol-1 in DMF) show that they are non-electrolytes. The molecular weight measurements indicate a monomeric structure of 2 and 5, while a dimeric structure of 3 (M = Co, Ni)

and 4. The loss of the coordinated MeOH molecule(s) occur between 80-120 oC in 2-5. LH3 acts as a dibasic tridentate ONO donor ligand. The (MO) and (MN) stretches occur between 540-570 and 420-450 cm-1

respectively. The reduction of Racah parameter [from the free ion values: 971 cm-1 to 780.7 cm-1 for Co(II) and from 1030 cm-1 to 799.8 cm-1 for Ni(II)] and the values of % covalency in 3 [19.5 when M = Co(II) and 23.0 when M = Ni(II)] are indicative of covalent nature of these coordination compounds. 1 exhibits multiplet at 6.82-8.00 ppm

ii

due to the aromatic protons, a singlet at 7.32 ppm due to the azomethine proton, a broad signal at 10.91 ppm due to the phenolic proton and a singlet at 11.73 ppm due to the NH proton. The appearance of alcoholic proton (singlet, 1H) at 2.74 ppm and methyl protons at 3.58 ppm in 2 confirms the presence of coordinated MeOH. The reduced magnetic moments of 3 (M = Co, Ni) and 4 may be due to the magnetic interaction between the two metal ions connected by phenoxo bridge. A tetrahedral geometry to 2, an octahedral geometry to 3 (M = Co, Ni) and 4 and a pentagonal-bipyramidal geometry to 5 have been assigned. The energy optimized structures, 6 and 7 for 1 and 2 respectively are proposed using the semiempirical ZINDO/1 quantum mechanical calculations.

Chapter 2 This Chapter describes the syntheses of the azetidin-2-one, L'H3 (8) [obtained by

the cyclocondensation of 1 with chloroacetyl chloride (ClCH2COCl, CAC) in the presence of triethylamine (Et3N) in dioxane]. A MeOH solution of Cu(II), Cd(II), Mn(II), Fe(III) and MoO2(VI) ions reacts with 8 in 1:1 molar ratio and forms the monomeric coordination compounds, [Cu(OAc)(L'H2)] (9), [Cd(OAc)(L'H2)] (10), [Mn(OAc)(L'H2)(MeOH)2] (11), [FeCl2(L'H2)(MeOH)] (12) and [MoO2(acac)(L'H2)(MeOH)] (13) respectively. The coordination compounds have been characterized on the basis of elemental analyses, molar conductance, molecular weight, spectral (IR, reflectance and ESR) studies and magnetic susceptibility measurements. They are insoluble in H2O, MeOH, EtOH but

soluble in DMSO and DMF. They are non-electrolytes in DMF (M = 5.3-8.3 mho cm2 mol-1). 8 behaves as a monobasic tridentate ONO donor ligand. The acetato ligands are bonded to the central metal ions in a monodentate fashion in 9, 10 and 11. The ESR

spectral parameters of 9 [g|| (2.8) > g (2.08) > 2.0), A|| (1.50 10-2 cm-1, A = 3.0 10-3 cm-1) and G (3.50)] are typical of a tetragonal type geometry. The magnetic moments, 1.87, 5.81 and 5.78 B.M. for 9, 11 and 12 respectively account for their magnetically dilute nature. A square-planar structure for 9, a tetrahedral structure for 10, the octahedral structures for 11 and 12 are proposed. The coordination number of Mo is eight in 13. Chapter 3

This Chapter deals with the syntheses and characterization of a thiazolidin-4-one, L'H3 (14) [obtained by the cycloaddition reaction of LH3 (1) with mercaptoacetic acid (HSCH2COOH) in dry C6H6] and its coordination compounds with Cu(II), Co(II), Ni(II),

iii

MoO2(VI) and Zr(OH)2(IV) ions. 14 reacts with appropriate metal ions in 1:1 molar ratio in MeOH and produces the compounds, [Cu(OAc)(L'H2)] (15), [M(OAc)(L'H2)(MeOH)2] (16, M = Co, Ni), [MoO2(acac)(L'H2)(MeOH)] (17) and [Zr(OH)3(L'H2)] (18). The coordination compounds are air-stable, insoluble in H2O, MeOH, EtOH and soluble in

DMSO and DMF. They are non-electrolytes (M = 4.3-9.6 mho cm2 mol-1) in DMF. 14 behaves as a monobasic tridentate ONO donor ligand coordinating through its phenolic O (o-aminophenol moiety), N (o-aminophenol moiety) and O (thiazolidin-4-one moiety) atoms. The phenolic O (aldehydic moiety), N and S atoms (thiazolidin-4-one moiety) are not involved in coordination. The appearance of two new bands between 1564-1572 cm-1

[as(OAc)] and 1340-1352 cm-1 [s(OAc)] stretches indicates the presence of the coordinated acetato group in 15 and 16 (M = Co, Ni). The presence of coordinated MeOH molecule(s) in 16 (M = Co, Ni) and 17 is proposed on the basis of IR spectral studies. The reflectance spectra of 15 and 16 (M = Co, Ni) are consistent with square-planar and octahedral environment around metal ions. 14 exhibits the signals at 6.82-8.00, 7.32, 10.91 and 11.7 ppm due to the aromatic, azomethine, OH protons, andNH protons respectively. A square-planar structure for 15, an octahedral structure for 16 (M = Co, Ni) and 18 are proposed. Mo assumes a coordination number of eight in 17.

Chapter 4 This Chapter deals with the syntheses and characterization of polystyrene-anchored

Schiff base, PSCH2LH3 (19) and its coordination compounds. The nucleophilic addition reaction followed by the elimination of one H2O molecule between

polystyrene-3-formylsalicylate and o-hydroxyphenylurea in DMF in the presence o f ethyl acetate results in the format ion o f 19 . The lat ter reacts with a DMF swollen suspension of Cu(II), Cd(II), Mn(II), Fe(III) and MoO2(VI) ions and forms the corresponding polystyrene-anchored coordination compounds, [PSCH2LH2Cu(OAc)(DMF)] (20), [PSCH2LH2 Cd(OAc)(DMF)] (21), [PSCH2LH2Mn(OAc)(DMF)3] (22), [PSCH2LH2 FeCl2(DMF)2] (23) and [PSCH2LH2MoO2(acac)] (24 , acacH = pentane-2,4-dione) respect ively. The polystyrene-anchored coordination compounds (20-24) have been characterized on the basis of elemental analyses, spectral (IR, reflectance, ESR) studies and magnetic susceptibility measurements. The per cent reaction conversion (PRC) of the compounds

iv

lies between 44.8-81.3 and the metal binding capacity (MBC) of the ligand between 0.32-0.60 mmol of metal per g of the resin. The coordinated DMF molecules are completely lost from the polystyrene-anchored coordination compounds by heat ing them at a

definite temperature in an air-oven for 3 h . 19

acts as a monobasic bidentate ON donor ligand in these compounds. 20 shows usual anisotropic pattern with two g values, which are characteristic of axial symmetry. 20 , 22 and 23 are paramagnetic and magnetically dilute. A square-planar structure for 20 , a tetrahedral structure for 21and the octahedral structures for 22, 23 and 24 are proposed.

IINNTTRROODDUUCCTTIIOONN

1

The Introductory Part of the Thesis entitled Studies on the Metal Complexes of First and Second Transition Series consists the Literature Survey on the coordination compounds of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Zr(OH)2(IV), MoO2(VI) and Cd(II) ions. A metal coordination compound is the aggregate of Lewis acid (electron pair acceptor central metal atom or metal ion having vacant d- or f- orbitals) and Lewis base(s) (electron pair donor anion, cation or neutral entity). A brief summary of the coordination compounds of the above metal ions with monodentate, bidentate, tridentate, tetradentate

and polydentate ligands are presented here.

Coordination compounds of manganese(II) Mangnese (Mn) is a greyish-white transition metal belonging to Group 7 and

Period IV of the Periodic Table. Its atomic number, atomic weight and the electronic configurations are 25, 54.93 amu and [Ar] 4s23d5 respectively. Its common oxidation states are +2, +3, +4, +6 and +7. Mn ions have various colours depending upon their oxidation state and they are generally paramagnetic. The most stable oxidation state of Mn

is +2, which has pink to red colour. Mn(II) ion acts as a cofactor for a number of enzymes in higher organisms, where they are essential in detoxification of superoxide free radicals. It is an essential trace nutrient in all forms of life. The ability of Mn(II) ion to form the coordination compounds with a wide range of ligands has been reported. These ligands are

coordinated to Mn(II) ion in a monodentate, bidentate, tridentate, tetradentate, pentadentate and hexadentate fashion. We present here a brief survey of the Chemistry of coordination compounds of Mn(II) ion. A. With monodentate ligands:

The synthesis of centrosymmetric compound, bis[-(E)-1,5-dimethyl-2-phenyl-4-(3-pyridylmethyleneamino)pyrazol-3(2H)-one]bis{dibromido[(E)-1,5-dimethyl-2-phenyl-4-(3-pyridylmethyleneamino)pyrazol-3(2H)-one]manganese(II)}, [Mn2Br4(C17H16N4O)4] has been reported[1]. In the crystal structure, the Mn atom adopts a trigonal-bipyramidal

geometry and the ligand adopts two coordination modes, monodentate and bidentate bridging.

2

B. With bidentate ligands:

Maurya et al.[2] have synthesized a reddish-brown, non-electrolyte (M = 10.5 mho cm2 mol-1), four-coordinate compound, [Mn(OAc)L(H2O)] (where LH = 25; R = 3-OMe, R' = OH, R'' = H) by refluxing a mixture of an EtOH solution of Mn(OAc)24H2O and a DMF solution of LH in 1:1 molar ratio for 4 h. It decomposes at 260 oC. It is soluble in DMF and DMSO. LH behaves as a monobasic bidentate ON donor ligand coordinating through its phenolic O and azomethine N atoms. The acetato ligand is coordinated to the metal ion in a monodentate fashion. The (MnO) and the (MnN) vibrations occur at 510 an 435 cm-1 respectively. Its magnetic moment is 5.94 B.M.

The six-coordinate heterochelate, [MnL2L'] [here LH = 25, R = 5-Cl, 5-Br; R' = OH; R'' = H; L' = 26, R = R' = H; R'' = Me; R''' = (CH2)2] has been synthesized[3]. LH acts as a monobasic bidentate ON donor ligand coordinating through its phenolic O and

azomethine N atoms, whereas L'

acts as a neutral NN donor ligand coordinating through its azomethine N atoms. The heterochelates exhibit three weak bands at ~15000, ~19000 and ~25500 cm-1 due to the 6A1g 4T1g(G)(1), 6A1g 4T2g(G)(2) and 6A1g 4A1g(G)(3) transitions respectively for octahedral geometry. The magnetic moments of the

heterochelates are 6.00 and 6.01 BM.respectively. The heterochelates show higher antimicrobial activity against S. typhi, F. oxysporum, S. cereusisae and L. theobromae than LH. The enhanced antimicrobial activity of the heterochelates against these microbes is due to the presence of two halogen and four azomethine groups. An octahedral structure (27, R = 5-Cl, 5-Br; M = Mn) has been suggested for the heterochelates.

The reaction of 2-aminophenol with Mn(II) ions in 1:1 molar ratio produces the aminophenolate compound as precipitate (in solution), which on further treatment with 4-benzyloxybenzaldehyde or but-2-enal in the above molar ratio yields the six-coordinate, orange-yellow compound, [MnL2(H2O)2] or brown compound, [MnL'2(H2O)2] respectively (where LH and L'H = 28 and 29 respectively)[4]. They melt at 180 and 200 oC respectively. They display two bands one at 16667, 16393 cm-1 and another at 20704, 20000 cm-1 respectively indicating the presence of an octahedral environment around the metal ion. They exhibit the magnetic moments 5.94 and 5.78 B.M. respectively, corresponding to high-spin octahedral symmetry due to five unpaired electrons. The coordination compounds are more biologically active against S. dysenteria, E. coli (responsible for

3

diarrhoea), P. aeruginosa, B. subtilis (responsible for contamination), S. lutea and S. aureus (responsible for wound infection) than 2-aminophenol.

Due to the formation of stable coordination compounds with heavy metal ions,

aroylhydrazones have been employed as specific reagents in analytical and extraction chemistry[5]. A red, four-coordinate compound, [Mn(LH)2] (where LH2 = 30, R = H) is obtained when an EtOH solution of LH2 and Mn(OAc)24H2O in 2:1 molar ratio are refluxed in the presence of TEM[6]. It decomposes at 274 oC and its molar conductance is

43 mho cm2 mol-1. LH2 acts as a monobasic bidentate ON donor ligand coordinating through its enolic O and azomethine N atoms. C. With tridentate ligands:

A monomeric, dark-brown, six-coordinate, polystyrene-anchored coordination

compound, [PSLMn(DMF)3] (here PSLH2 = 31) is obtained[7] by refluxing a DMF swollen suspension of Mn(OAc)24H2O and PSLH2 for 8 h. The Schiff base acts as a dibasic tridentate ONO donor ligand. The DMF molecules are coordinated to the metal ion. The PRC of the compound is 78.6. The MBC of the ligand is 0.60 mmol of metal per g of it. Its magnetic moment is 5.92 B.M. It displays three bands at 18440, 22980 and 25220 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4A1g(G) spin-forbidden transitions respectively.

The heterochelates containing O and N atoms are important owing to their

significant antifungal, antibacterial and anticancer activity. The pale-brown compound, [Mn5Cl10(LH2)(H2O)9] and the black heterochelate, [Mn2Cl3(LH2)(acac)(H2O)] (where LH2 = 32) have been synthesized[8]. They are non-electrolytes. The ligand acts as a neutral tridentate ONO donor. The central Mn(II) ions in both the cases are held together by bridged chloro ligands and the remaining coordination sites are occupied by O atom of water molecules. The appearance of three bands at 25640, 22222, 17240 and 25315, 20833, 16805 cm-1 and the low magnetic moments (2.5 and 3.1 BM) respectively of the compound/ heterochelate due to super-exchange suggest their octahedral geometry around

the metal ions.

A dark-brown, six-coordinate, polystyrene-anchored compound,

[PSCH2LMn(DMF)3] (where PSCH2LH2 = 33; R = 3-PSCH2OCO, X = O) has been synthesized by refluxing Mn(OAc)24H2O and the ligand in 2:1 molar ratio in DMF[9]. The

4

Schiff base acts as a dibasic tridentate ONO donor ligand coordinating through its phenolic O, azomethine N and enolic O atoms. The furanoic O atom does not participate towards coordination as evident by the unaltered (COC) stretch (1080 cm-1) both in ligand and the compound. Its magnetic moment is 5.85 B.M. The appearance of two bands one at 16395 cm-1 and another at 24600 cm-1 due to the 6A1g 4T1g(G) and 6A1g 4T2g(G) transitions is indicative of an octahedral environment around the metal ion.

Kumar et al.[10]

have synthesized a dark-brown, polystyrene-anchored six-

coordinate compound, [PSCH2LHMn(DMF)3] (where PSCH2LH3 = 34) by refluxing a DMF swollen suspension of PSCH2LH3 and a DMF solution of Mn(OAc)24H2O. The PRC of the compound is 93.3 and the MBC of PSCH2LH3 is 0.58 mmol of Mn per g of the ligand. PSCH2LH3 behaves as a dibasic tridentate ONO donor ligand. The magnetic

moment (5.9 B.M.) and the appearance of two bands one at 16000 and another at 22500 cm-1 due to the 6A1g 4T1g(G) and 6A1g 4T2g(G) transitions respectively indicate an octahedral environment around the metal ion.

A deep-brown, binuclear, six-coordinate compound, [Mn2L2(H2O)4] is obtained by stirring an EtOH solution of Mn(OAc)24H2O and LH2 (35A-35C) in 1:1 molar ratio in the presence of LiOH for 4 h[11]. It melts at 198 oC. It is soluble in Me2CO but insoluble in MeOH. The ligand behaves as a dibasic tridentate OON donor. The lower value of the magnetic moment (5.39 B.M.) indicates the presence of an anti-ferromagnetic interaction between the adjacent metal cations. An octahedral geometry 36 (M = Mn; A = H2O) has been suggested for the compound.

The synthesis of a light-yellow, four-coordinate, non-electrolyte (in DMSO), [MnCl(LH)]3H2O (where LH2 = cephalexin, 37) has been reported[12]. It is air-stable, soluble in DMSO and DMF, slightly soluble in MeCN. The coordination of the ligand

occurs through the carboxylato O, carbonyl O (-lactam) and N atom of NH2 group. The carboxylato group is coordinated in a monodentate mode ( = 235 cm-1). A mass loss equivalent to three water molecules in the 90-110 oC range suggests that these molecules are not coordinated to the metal ion. The magnetic moment (5.6 B.M.) indicates the presence of five unpaired electrons. A tetrahedral structure (38, M = Mn) has been assigned to it.

5

A four-coordinate compound, [MnCl(LH)]3H2O (here LH2 = 39) has been synthesized by stirring a MeOH solution of NaHL and MnCl24H2O in 2:1 molar ratio

for 8 h at room temperature[13]. It is air-stable, soluble in DMSO and DMF and slightly soluble in MeCN. The (C==O)(-lactam) stretch of the ligand occurring at 1780 cm-1 shifts to 1720 cm-1 in the coordination compound indicating the involvement of carbonyl O atom towards coordination. The overlapped (C==O)(amide) and (C==O)(ester) bands in LH2 appears at 1640 cm-1. These bands remain unchanged in the compound suggesting that coordination of the ligand occurs through the O atom from the lactam carbonyl group

rather than the amide and ester carbonyl groups. The carboxylato group is coordinated in a monodentate mode ( = 240 cm-1). The amino group of LH2 is coordinated to the metal ion as evident by the presence of the (MnN) stretch at 450 cm-1. Thus, LH2 behaves as a monobasic tridentate OON donor ligand. The compound has a magnetic moment of 5.4 B.M. It shows higher activity than LH2 against P. mirabilis, K. pneumoniae, S. enteriditis and E. coli, while it remains inactive towards S. aureus and P. aeruginosa. A tetrahedral structure (40, M = Mn) has been assigned to it.

Hankare et al.[14] have synthesized a brown, dimeric, four-coordinate, non-

electrolyte, high-spin compound, [Mn2Cl2L2] [here LH = 41, the Schiff base obtained from the condensation of 5-(2'-thiazolylazo)salicylaldehyde and 4-methoxyaniline] by refluxing an EtOH solution of MnCl24H2O and LH in 1:1 molar ratio. It is soluble in DMSO. The Schiff base acts as an ONN donor ligand coordinating through its phenolic O and azomethine N to one Mn(II) ion and through azo N atom to another Mn(II) ion.

Upon digesting an aqueous solution of Mn(OAc)24H2O and a DMF solution of LH (42; R = Me, R' = Ph) in 1:1 molar ratio for h, a six-coordinate compound, [MnL2] is obtained[15]. It is insoluble in common organic solvents but sparingly soluble in dioxane and DMF. The monobasic ligand coordinates to the metal ion through its pyrazolinic O,

azomethine N and thiazolic N atoms. The (MnO) and (MnN) vibrations occur at 460 and 390 cm-1 respectively in the coordination compound. Due to their doubly forbidden nature, it exhibits three very low intense bands at 16667, 23256 and 26316 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4Eg(G)/4A1g(G) transitions respectively indicating the octahedral environment around metal ions. The magnetic moment (6.05 B.M.) suggests its distorted octahedral geometry alongwith high-spin 3d5

6

configuration of the metal ion. The ligand and the coordination compound show antibacterial activity against E. coli, B. subtilis and S. aureus.

Chandole et al.[16] have synthesized the air-stable, non-hygroscopic, non-

electrolyte, dimeric, six-coordinate compound, [MnClL(H2O)]2 (here LH = 43; R = Me, Et, propyl) and [MnCl(L'H)(H2O)]2 (here L'H2 = 43; R = CH2CH2OH) by refluxing a MeOH solution of MnCl22H2O and LH or L'H2 in 1:1 molar ratio for 4 h. They are soluble in DMF and DMSO. The coordinated water molecules are lost between 190-200 oC. Although L'H2 is potentially a dibasic tetradentate NONO donor ligand but similar to LH, it also behaves as a monobasic tridentate NON donor ligand bridging through its enolic O atom. The coordination compounds display three bands between 16835-16949, ~23584 and ~26385 cm-1 due to the 6A1g 4T1g(G)(1), 6A1g 4T2g(G)(2) and 6A1g 4Eg(G)(3) transitions respectively indicating the octahedral environment around the metal ion. Their magnetic moments lie between 4.88-5.07 B.M. The compound (when R = Me) crystallizes in a monoclinic fashion with a = b = 4.92 , c = 5.41 , = = 90, = 120. They exhibit higher antifungal activity against A. niger than the corresponding ligands. A distorted octahedral structure (44, M = Mn) has been suggested for them.

On refluxing an hot MeOH solution of Mn(NO3)26H2O and LH (45) in 1:2 molar ratio at pH = 7.5-8.5, a brown, six-coordinate complex, [MnL2] is obtained[17]. The complex is non-electrolyte (M = 10.02 mho cm2 mol-1 in DMSO). LH acts as a monobasic tridentate ONN donor ligand coordinating through its phenolic O and both azomethine N atoms. The magnetic moment (5.7 B.M.) and the appearance of the bands at 16611, 24390 and 26881 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4Eg transitions respectively indicate the presence of an octahedral environment around the metal ion. The complex crystallizes in monoclinic fashion with a = 14.223 , b = 5.196 , c = 7.754 . The compound shows higher antimicrobial activity against Gram-negative E. coli, Gram-positive S. aureus and LH.

The coordination compounds of Schiff bases containing S atom have received considerable attention during recent past, primarily due to the remarkable antitumor, antibacterial and antiviral properties[18,19]. The complexation of yellow colored benzothiazoline derivative, 3-(2,3-dihydro-1,3-benzothiazole-2-yl)quinoxalin-2(1H)-one (LH2 = 46A, 46B) with Mn(II) ion proceeds with the rearrangement of benzothiazoline

7

ring to form the corresponding red colored, non-electrolyte, [Mn(LH)(OAc)(H2O)2][20]. In the presence of Mn(II) ion, the benzothiazoline rearranges to form the Schiff base (LH2). The latter coordinates in keto form as monobasic tridentate ONS donor. The magnetic

moment (5.80 B. M.) and the existence of the bands at 24814, 23529 and 21413 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4Eg transitions respectively, are indicative of an octahedral environment around the Mn(II) ion. The loss of coordinated water molecules occurs between

150-200 oC. Makode et al.[21] have synthesized a light-green, dimeric, six-coordinate

compound, [MnL(H2O)2]2 (where LH2 = 47) by refluxing Mn(OAc)24H2O and LH2 in EtOH. Although LH2 is potentially a dibasic pentadentate ONNSS donor ligand, but

behaves as a dibasic tridentate ONS donor ligand. The phenolic O, azomethine N and the thioenolic S afford the coordination sites of the octahedron. The value of magnetic

moment (5.14 B.M.) and the appearance of three bands due to the 6A1g 4T1g, 6A1g 4T2g and

6A1g 4A1g transitions indicate its octahedral stereochemistry. Both the coordinated

H2O molecules are lost between 160-210 oC. It shows activity against E. aureus, P. mirabilis and S. typhi.

An aqueous solution of Mn(OAc)24H2O reacts with an EtOH solution of LH2 (48) in 1:2 molar ratio and forms[22] a yellow compound, [Mn(LH)2]. It is stable in air, decomposes at 201 oC, insoluble in EtOH, C6H6 and CHCl3 but soluble in Me2CO, DMF and DMSO. It is non-electrolyte in DMSO and Me2CO. LH2 acts as a monobasic tridentate ONS donor ligand. The (MnN) vibrations occur at 565 cm-1 in the compound. The magnetic moment (5.9 B.M.) indicates the presence of high-spin octahedral environment around the metal ion. The compound assumes a six-coordinate structure (49, M = Mn).

A four-coordinate, air-stable, non-electrolyte (in DMSO), [MnCl(LH)] (where LH2 = cephalothin, 50; R = H, R' = Me) has been synthesized by stirring a MeOH solution of MnCl24H2O and LH2 in 1:2 molar ratio[23]. It is soluble in DMSO and DMF, slightly soluble in MeCN and insoluble in MeOH and H2O. The (C==O)(-lactam) stretch of LH2 shifts from 1730 to 1690 cm-1 in the compound indicating the involvement of O atom towards coordination. The (C==O)(amide) stretch of LH2 occuring at 1650 cm-1 remains unchanged in the compound indicating its non-involvement towards coordination. The

8

as(COO) and s(COO) stretches of LH2 occurring at 1620 and 1400 cm-1 shift to 1615 and 1380 cm-1 respectively in the compound indicating monodentate behaviour of the carboxylato group ( = 235 cm-1). LH2 acts as a monobasic tridentate OOS donor ligand. The presence of MS stretch indicates the coordination through thiophene S atom. The value of magnetic moment (5.5 B.M.) indicates the presence of five unpaired electrons. It shows a very weak absorption band at 25640 cm-1 due to a spin-orbit forbidden transition. It shows antibacterial activity higher than the ligand against S. aureus, E. coli, S.

enteriditis and P. mirabilis, while it shows no activity against K. pneumoniae. A tetrahedral structure (51; R = H, R' = Me, M = Mn, A = nil) has been assigned to it.

An EtOH solution of MnCl24H2O and LH [here LH = 52, R = (C5H4N)CH, R' = NH C6H4(4-OMe); L'H = 52, R = (C5H4N)CH, R' = NHCH2CH2C6H5; L''H = 52, R = (C5H4N)CH, R' = N(Me)C6H5; X = S] in 1:2 molar ratio upon refluxing[24] produce brown-orange, six-coordinate, non-electrolyte, [MnL2]H2OEtOH, [MnL'2]3H2O, [MnL''2]3H2O; brown, six-coordinate, 1:1 electrolyte, [MnL(LH)](OAc) and brown, six-coordinate, 1:2 electrolyte, [Mn(L''H)2](SCN)2MeOH. The ligands behave as a monobasic tridentate NNS donors in [MnL2]H2OEtOH, [MnL'2]3H2O, [MnL''2]3H2O; neutral tridentate NNS donor in [Mn(L''H)2](SCN)2MeOH and neutral as well as monobasic tridentate NNS donor in [MnL(LH)](OAc). The magnetic moments are 6.02, 5.33, 5.56, 5.62 and 5.81 B.M. for [MnL2]H2OEtOH, [MnL'2]3H2O, [MnL''2]3H2O, [MnL(LH)](OAc) and [Mn(L''H)2](SCN)2MeOH respectively. A broad band at 22936, 23419, 23148, 23810 and 23542 cm-1 due to the 6A1g 4T2g(G) transition and a very week band at 18248, 18903, 18867, 18051 and 18478 cm-1 due to the 6A1g 4T1g(G)(2) transition respectively occur in [MnL2]H2OEtOH, [MnL'2]3H2O, [MnL''2]3H2O, [MnL(LH)](OAc) and [Mn(L''H)2](SCN)2MeOH respectively. [MnL2]H2OEtOH crystallizes in a monoclinic fashion with a = 15.164 , b = 18.793 , c = 11.896 ; = = 90.0o, = 109.31o and Z = 8. An octahedral geometry is assigned to them. D. With tetradentate ligands:

Kumar et al.[25] have become the first to synthesize a polystyrene-anchored asymmetric Schiff base, PSCH2LH2 [53; R = R' = Me, R'' = (CH2)2] and its brown, six-coordinate compound, [PSCH2LMn(DMF)2]. The Schiff base acts as a dibasic tetradentate ONNO donor ligand. The magnetic moment of the compound (5.92 B.M.) and

9

the occurrence of two bands one at 16950 cm-1 and other at 24400 cm-1 are characteristic of its octahedral geometry around Mn(II) ion.

Hasnain et al.[26] have reported the two step syntheses of Mn chelated

polyurethane containing LH2

(54) as the Schiff base. In the first step, a DMSO solution of LH2 refluxed with Mn(OAc)24H2O in DMSO forms a mustard coloured complex, [MnL(H2O)2]. In the second step, the polyaddition of toluene-2,4-diisocyanate with [MnL(H2O)2] is carried out in the presence of di-n-butyltindilaurate. The ligand behaves as a tetradentate ONNO donor in both the compounds coordinating through its phenolic O and N atoms of thiosemicarbazide moieties. The high-spin octahedral polymeric complex

(5.68 B.M.) displays three bands at 16200, 19400 and 22980 cm-1 due to the 6A1g 4T1g, 6A1g 4T2g and 6A1g 4A1g spin-forbidden transitions respectively. The antimicrobial

studies show that metal chelated polyurathane is more active than [MnL(H2O)2]. A four-coordinate, air-stable compound, [MnL] (where LH2 = 55) has been

synthesized by refluxing a MeOH solution of Mn(OAc)24H2O and a CH2Cl2 solution of LH2 in 1:1 molar ratio for 17 h[27]. It is readily soluble in DMF, DMSO and CHCl3, sparingly soluble in MeOH and EtOH and insoluble in non-polar solvents. The IR data are

indicative of the dibasic tetradentate ONNO donor nature of the ligand. The compound shows magnetic moment of 1.9 B.M. indicating the presence of one unpaired electron.

A brown, six-coordinate, monomeric compound, [Mn(LH2)(H2O)2] (where LH4 = 56) has been synthesized[28]. LH4 acts as a dibasic tetradentate ONNO donor ligand. The coordinated H2O molecules are lost at about 170 oC. The magnetic moment of the compound is 5.62 B.M.

A brown, low-spin, six-coordinate compound, [Mn(LH2)(H2O)2] (where LH4 = 57) is obtained by stirring MnSO4H2O and LH4 in H2O-EtOH solution[29]. Interestingly, a yellow, high-spin, six-coordinate compound, [Mn(LH2)(H2O)2] is obtained by stirring MnCl24H2O and ligand in EtOH. The Schiff base behaves as a dibasic tetradentate ONNO donor ligand in both the compounds. The magnetic moment of the low-spin compound is 1.85 B.M. and it exhibits two ESR signals one at g = 2.03 and another at g = 4.4 at LNT. The high-spin compound affords the magnetic moment of 5.90 B.M.

A brown, four-coordinate, thermally-stable, binuclear compound, [MnL]2 (where LH2 = 58) has been synthesized by Maurya et al.[30]. LH2 behaves as a dibasic tetradentate

10

ONNO donor ligand. The magnetic moment (5.74 BM) of the compound is indicative of high-spin, tetrahedral environment around both Mn(II) ions.

A six-coordinate, non-electrolyte compound, [MnL(H2O)2] [where LH2 = 59) has been synthesized[31]. LH2 behaves as a dibasic tetradentate ONOO donor ligand coordinating through its phenolic O, azomethine N, carbonyl O and nitroso O atoms. The magnetic moment of the compound is 4.30 B.M.

Manjunathan et al.[32] have synthesized a four-coordinate, 1:1 electrolyte, [MnL]Cl (where LH = 60) by refluxing LH and MnCl24H2O in EtOH for 1.5 h. LH acts as a monobasic tetradentate ONNN donor ligand coordinating through its phenolic O, both azomethine N and anilinic N atoms. The compound shows six hyperfine lines with g|| =

2.0236 and g = 2.004. A square-planar geometry has been suggested to it.

An air-stable, six-coordinate, slightly ionized (M =13.0 mho cm2 mol-1 in DMF) complex, [MnLCl2]H2O (here L = 61) is obtained by reacting MnCl2 and L in EtOH[33]. L behaves as a neutral tetradentate N4 donor ligand coordinating through its both azomethine and pyridyl ring N atoms. The (MCl)

vibration occurs at 224 cm-1. The chloro ligands occupy the axial coordination sites.

The light-brown, cube-shaped crystalline, seven-coordinate dinuclear Mn(II) complex, [Mn2L2(1,5-dca)2(dca)2]H2O [L = N,N'-ethylenebis(2-benzoylpyridineimine), dca = dicyanamide] is obtained by refluxing an equimolar mixture of Mn(NO3)2, L and dca in EtOH[34]. The molar conductances of the complex are 246 and 212 mho cm2 mol-1 in MeOH and MeCN respectively indicating its existence as a 1:2 electrolytes in these

solvents. The complete loss of H2O molecule occurs at ~175 oC and [Mn2L2(1,5-dca)2(dca)2] is obtained. Mn2O3 is the end product at 480 oC. L behaves as a neutral tetradentate N4 donor ligand. The effective magnetic moment of the complex is 8.36 B.M. The complex crystallizes in an orthorhombic fashion. Two [Mn(II)L] units are doubly bridged by dicyanamide ligands in a 1,5 pattern. The molecule of the complex possesses a centre of inversion at the mid point of the line bisecting the adjacent metal centers of the dimeric unit. The dca ligands are involved in coordination with the metal center via monodentate and 1,5 bridging patterns. The pentagonal base is provided by five N atoms,

four from L and one from one of the bridging dca moieties. The axial positions are occupied by a terminal dca and other by the bidging dca moiety. The axial MnN bonds

11

are shorter than the basal MnN bonds. A distorted pentagonal-bipyramidal structure has been assigned to the complex. The complex is an efficient catalyst for the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylbenzo- quinone under air in MeOH solution, but is inactive in MeCN. E. With pentadentate ligands:

A five-coordinate compound, [Mn(LH)]2H2O (here Na2LH = ceftriaxone, 62) has been synthesized by stirring a MeOH solution of Na2LH and MnCl24H2O in 1:1 molar

ratio for 1 h at room temperature[35]. It is air-stable and insoluble in H2O and EtOH, C6H6,

Me2CO, MeCN, Et2O, py, DMF and DMSO suggesting its polymeric nature. Na2LH behaves as a dibasic pentadentate ONOON donor ligand. The non-coordinated H2O molecules are lost between 80-110 oC. The magnetic moment of the compound is 6.1 B.M. It shows higher bactericidal activity than Na2LH against S. sonnei, P. mirabilis and P.

aeruginosa; lesser activity than Na2LH against S. aureus and S. enteritidis. A five-coordinate structure (63, M = Mn) has been assigned to it.

The synthesis of a monomeric, seven-coordinate compound, [Mn(LH2)(H2O)2](ClO4)2 (here LH2 = 64; R = R' = H) has been reported[36]. The Schiff base acts as a neutral pentadentate SNNNS donor ligand. The Mn ion is ligated to three N and two S atoms of the ligand forming the pentagonal girdle and O atoms of the water molecules occupying the apical positions. The ClO4 ions are involved in hydrogen bonding with the H2O molecules and with the terminal amino groups of the ligand. A distorted pentagonal-bipyramidal structure [65; M = Mn, A = H2O] has been suggested to it.

F. With hexadentate ligands: Salehzadeh et al.[37] have reported the synthesis of a monomeric, seven-coordinate,

1:1 electrolyte, [MnClL](ClO4) [here L = 66; R = 2-C5H4N]. L acts as a neutral hexadentate N6 donor ligand. The Mn(II) ion is coordinated to three py and three asymmetric tripodal amine N atoms. The environment around the Mn(II) ion is distorted pentagonal-bipyramid.

12

Coordination compounds of iron(III) Iron (Fe) is a greyish transition metal of Group 8 and Period IV of the Periodic

Table. Its atomic number, atomic weight and the electronic configurations are 26, 55.84 amu and [Ar] 3d64s2 respectively. It is associated with ferromagnetic properties. Its common oxidation states are +2 and +3. Ferrous ion (Fe2+) is necessary trace element in living organisms. It is present in hemoglobin, myoglobin, cytochrome system. Iron containing enzymes usually containing heme prosthetic groups participate in catalysis of

oxidation reactions in biology. The ability of Fe(III) ion to form the coordination compounds with a wide range of ligands has been reported. These ligands are coordinated to Fe(III) ion in a bidentate, tridentate, tetradentate, pentadentate and hexadentate fashions. We present here a brief survey of the Chemistry of coordination compounds of Fe(III) ion. A. With bidentate ligands:

The synthesis of a brown, high-spin, six-coordinate compound, [FeCl2L(PPh3)2] (where LH = 25, R = H, C4H4; R' = OH; R'' = H, Cl, Me, OMe) has been reported[38]. The IR data indicate the monobasic bidentate ON donor behaviour of LH. The compounds

have been used as catalysts in aryl-aryl coupling reactions between phenylmagnesium bromide and phenyl bromide to yield biphenyl.

The reaction of 2-aminophenol with Fe(III) ions produces the aminophenolate coordination compound as precipitate (in solution), which on further treatment with 4-benzyloxybenzaldehyde or but-2-enal in 1:1:1 molar ratios yields[4] the deep-brown, six-coordinate compounds, [FeClL2(H2O)] or [FeClL'2(H2O)] (where LH and L'H = 28 and 29 respectively). They melt at 290 and 190 oC respectively. Both LH and L'H act as the monobasic bidentate ON donor ligands. The former displays the (FeO) and (FeN) vibrations at 600 and 508 cm-1 respectively, while the latter displays these vibrations at 582 and 428 cm-1 respectively. Their magnetic moments (5.97 and 6.00 B.M. respectively) correspond to the presence of five unpaired electrons in a high-spin octahedral Fe(III) compound. These values are very close to the spin-only value (5.90 B.M.) since the ground state (derived from 5S state of free ion) has no orbital angular momentum. [FeClL2(H2O)] displays the molecular ion peak at 713 (M+) and 302 (100%, C6H5CH2OC6H4CN==C6H4O)+. Another compound, [FeClL'2(H2O)] displays the molecular ion peak at 429 (M+) and 160 (100%, CH3CHCHCHNC6H4O)+. They are

13

biologically more active against S. dysenteria, E. coli, P. aeruginosa, B. subtilis, S. lutea and S. aureus than 2-aminophenol.

On refluxing an EtOH solution of FeCl3 (anhydrous) and LH (67) in 1:2 molar ratio for 2 h, a black dimeric coordination compound, [FeClL2]2 is obtained[39]. It is non-hygroscopic, air-stable, decomposes above 230 oC, soluble in DMF and DMSO but partially soluble in MeOH, EtOH, MeCN, PhNO2 and CHCl3. It is non-electrolyte in MeOH and PhNO2. The ligand is coordinated to the metal ion through its phenolic O and

azomethine N atoms. The low value of the magnetic moment (5.3 B.M.) indicates the bridged structure involving an anti-ferromagnetic exchange interaction. A dimeric octahedral structure has been suggested for it.

The synthesis of a brown, six-coordinate, polystyrene-anchored coordination

compound, [PSCH2LFeCl2(DMF)2] (here PSCH2LH = 68) has been reported[25]. The ligand acts as a monobasic bidentate ON donor ligand. The magnetic moment (6.00 B.M.) and the appearance of three bands at 12200, 15500 and 19000 cm-1 suggest an octahedral geometry around Fe(III) ion. B. With tridentate ligands:

The dark-brown, six-coordinate, polystyrene-anchored coordination compound, [PSLFeCl(DMF)2] (where PSLH2 = 31) is obtained by refluxing a DMF swollen suspension of PSLH2 and anhydrous FeCl3 for 6 h[7]. Its PRC is 93.7. The MBC of the ligand is 0.73 mmol of metal per g of it. The dibasic tridentate ligand coordinates through its phenolic O, azomethine N and alcoholic O atoms. The magnetic moment of the compound is 5.87 B.M. The latter displays three bands at 12720, 19600 and 25000 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G), 6A1g 4A1g(G) spin-forbidden transitions respectively suggesting its octahedral geometry.

The brown coloured compound, [Fe3Cl8(LH)(H2O)3]2H2O and the red coloured [FeL(acac)(H2O)]H2O have been synthesized by reacting FeCl3 and LH2 (32) in the presence and absence of Et3N respectively[8]. LH2 acts as a monobasic tridentate ONO

donor ligand in the former and as a dibasic tridentate ONO donor ligand in the latter. The lower value of magnetic moment (3.7 B.M.) for the brown compound is due to the spin-density exchange between the iron(III) centers. The value of magnetic moment (5.9 B.M.) for the red compound indicates its octahedral geometry. They are more potent fungicides

14

and bactericides than the ligand. A chloro-bridged structure has been suggested for the brown compound.

A DMF swollen suspension of PSCH2LH2 (33; R = 3-PSCH2OCO, X = O) upon refluxing with anhydrous FeCl3 produces[9] a brown, six-coordinate compound,

[PSCH2LFeCl(DMF)2]. The Schiff base acts as a dibasic tridentate ONO donor ligand coordinating through its phenolic O, azomethine N and enolic O atoms. The furanoic O atom does not participate towards coordination. The magnetic moment (5.98 B.M.) and the appearance of three bands at 12500, 17420 and 25000 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4A1g(G) transitions are indicative of an octahedral environment around the metal ion.

Kumar et al.[10]

have synthesized a reddish-brown, polystyrene-anchored, six-coordinate compound, [PSCH2LHFeCl(DMF)2] (where PSCH2LH3 = 34) by refluxing a DMF swollen suspension of PSCH2LH3 and a DMF solution of anhydrous FeCl3 The

PRC of the compound is 64.2 and the MBC of PSCH2LH3 is 0.41 mmol of Fe per g of the ligand. The ligand behaves as a dibasic tridentate ONO donor. The magnetic moment (5.96 B.M.) and the appearance of three bands at 13000, 17100 and 25100 cm-1 due to the 6A1g 4T1g (G), 6A1g 4T2g (G), 6A1g 4A1g (G) indicate an octahedral environment around the metal ion.

The synthesis of a six-coordinate compound, [FeX2L(H2O)]2H2O (here LH = 69, X = Cl, NO3) has been reported[40]. LH acts as a monobasic tridentate ONO donor ligand. [FeCl2L(H2O)]2H2O shows three bands due to the presence of both high-spin Fe(III) (S = 5/2) and low-spin Fe(III) (S = 1/2) ions within the same crystal lattice indicating its octahedral geometry.

The synthesis of a brown, dinuclear coordination compound, [Fe2L2(NO3)2]H2O (here LH2 = 70, X = NH2) has been reported[41]. It melts above 280 oC and is soluble in common organic solvents but partially soluble in DMF and DMSO. LH2 behaves as a bis(monobasic tridentate) ONN donor ligand. The appearance of two new bands at 1384 and 856 cm-1 indicates the presence of coordinated nitrato group in the compound. The (FeO) and the (FeN) vibrations occur at 580 and 454 cm-1 respectively. The low value of magnetic moment (4.95 B.M.) of the compound suggests the presence of an anti-

15

ferromagnetic interaction acting between the neighbouring Fe(III) ions. The lattice H2O molecules are lost by heating the compound between 40-97 oC.

The brown, six-coordinate complex, [FeL2](NO3) (here LH = 45) is obtained[17] on refluxing an hot MeOH solution of Fe(NO3)39H2O and LH in 1:2 molar ratio at pH = 7.5-8.5. LH

acts as a monobasic tridentate ONN donor ligand coordinating through phenolic O and both azomethine N atoms. The magnetic moment (5.85 B.M.) and the appearance of three bands at 12658, 18940 and 30864 cm-1 due to the 6A1g 4T1g(G), 6A1g 4T2g(G) and 6A1g 4A1g(G) transitions respectively indicate the presence of an octahedral environment around the metal ions. The compound shows higher antimicrobial activity against Gram-negative E. coli, Gram-positive S. aureus and LH.

A reddish-brown, six-coordinate, dinuclear compound, [Fe2Cl4(LH)2]2EtOH (here LH2 = 35A-35C) is obtained by stirring an EtOH solution of FeCl36H2O and LH2 in 1:2 molar ratio for 4 h[11]. It melts at 160 oC. It is soluble in MeOH but insoluble in H2O and

Et2O. The rather higher value of molar conductance (M = 58.0 mho cm2 mol-1) in DMF is due to the partial replacement of the chloro ligands with DMF molecules. The IR data are indicative of the monobasic tridentate OON donor behaviour of the ligand. The compound

shows two broad bands one at 18797 cm-1 and other at 25510 cm-1 due to the spin-forbidden 6A1 4T2(G) and 6A1 4A1, 4E(G) transitions respectively. Its magnetic moment is 5.94 B.M. and that of a single Fe(III) ion is 4.20 B.M. Thus, there occurs an anti-ferromagnetic interaction between the adjacent Fe(III) ions. The unsymmetrical broad band at g = 1.827 indicates a distorted octahedral geometry around the Fe(III) ions. The compound consists of two mononuclear units, where the cations in each unit are coordinated to OON sites of a ligand and are linked together by Cl atoms. An octahedral structure (71) has been assigned to it.

A non-electrolyte, five-coordinate compound, [FeCl2(LH)]3H2O (72) (here LH2 = 39) has been synthesized by stirring a MeOH solution of NaHL and FeCl36H2O in 2:1 molar ratio for 8 h at room temperature[42]. It is air-stable, soluble in DMSO and DMF and slightly soluble in MeCN. NaHL behaves as a monobasic tridentate OON donor ligand. The carboxylato group coordinates in a monodentate fashion. The compound has a

magnetic moment of 4.6 B.M. which lies between the values expected for the Fe(III) coordination compounds with S = 5/2 and S = 1/2 suggesting the possibility of spin-state

16

equilibrium between 6A2 and 2T2 states respectively. It shows weak absorption at 23810 cm-1 due to the spin-orbit forbidden transitions. The latter shows higher bactericidal activity than LH2 against P. mirabilis, K. pneumoniae, S. enteriditis and E. coli, while it

remains inactive towards S. aureus and P. aeruginosa. A four-coordinate, 1:1 electrolyte (in DMSO), [FeCl(LH)]Cl (where LH2 =

cefoxitin, 50; R = OMe, R' = NH2) has been synthesized by stirring a MeOH solution of NaHL and FeCl36H2O in 1:1 molar ratio for 8 h in N2 atmosphere at room temperature[43].

It is air-stable, soluble in DMF and DMSO but slightly soluble in MeCN. NaHL behaves

as a monobasic tridentate OOS donor ligand. The carboxylato group coordinates in a monodentate mode. The presence of (MS) stretch at 300 cm-1 indicates coordination through S atom of thiophene moiety. Its magnetic moment is 6.1 B.M. It shows lesser bactericidal activity than LH2 against S. aureus, E. faecalis, E. coli, P. mirabilis, S. sonnei and S. enteritidis.

El-Sawaf et al.[44] have reported the synthesis of a brown, five-coordinate compound, [Fe(ClO4)2L] [where LH = 73]. LH coordinates through carbonyl O (pyrazolone ring), thiolato S and azomethine N atoms. The chlorato group coordinates in a monodentate fashion. The magnetic moment of the compound is 3.7 B.M. A square-pyramidal structure has been suggested for the latter. C. With tetradentate ligands:

Kumar et al.[25] have synthesized a reddish-brown, six-coordinate polystyrene-anchored coordination compound, [PSCH2LFeCl(DMF)] by refluxing a DMF swollen suspension of PSCH2LH2 [53; R = R' = Me, R'' = (CH2)2] and a DMF solution of anhydrous FeCl3 in 2:1 molar ratio in the presence of ethyl acetate and Et3N. Its PRC is 49.2. The MBC of the ligand is 0.34 mmol of metal per g of it. The Schiff base acts as a dibasic tetradentate ONNO donor ligand. The magnetic moment of the compound is 5.94 B.M. The three bands at 12650, 16970 and 25000 cm-1 in the latter are characteristic of octahedral geometry around Fe(III) ion.

Although LH2 (74) and L'H2 (75) are potentially the dibasic hexadentate NONNON donor and the dibasic heptadentate NONNNON donor ligands respectively,

they act as a dibasic tetradentate ONNO donors[45] in the black, mononuclear compound, [FeL1.5]3H2O and another black, binuclear compound, [Fe2L'3]. The former shows a

17

narrow band at 14493 cm-1 in nujol and a broad band at 15748 cm-1 in DMSO, while the latter shows a narrow band at 14493 cm-1 in nujol and a broad band at 16367 cm-1 in DMSO due to the spin-forbidden, 6A1g 4T2g(G) transition indicating the distorted octahedral environment due to the polymerization around the metal ion. Their magnetic moments are 3.86 and 3.38 B.M. respectively. The former displays gx, gy and gz signals at 2.216, 2.109 and 1.959 respectively, while these signals appear at 2.224, 2.115 and 1.959 respectively in the latter indicating severe distortion of the octahedral geometry in the

array in the solid state.

Saghatforoush et al.[46] have synthesized the six-coordinate, 1:2 electrolyte (M = 196-233 mho cm2 mol-1 in MeCN), [FeL(H2O)2]Cl2 [where LH = 5-R-N-(2-pyridylethylsulphanylethyl)salicylideneimine; R = OMe, N2Ph, I, NO2] (76) by refluxing a MeOH solution of FeCl36H2O and LH in 1:1 molar ratio in the presence of NaOH. They are light-brown to dark-brown crystalline solids, fairly soluble in MeOH, MeCN, DMF, DMSO and melt between 173-201 oC. LH coordinates through deprotonated phenolic O, imine N, thioether S and py N atoms and affording an octahedral geometry around the Fe(III) ion in the compounds. It decomposes (when R = I) before melting at 209 oC. The others melt before undergoing exothermic decomposition. They undergo two-step degradation reactions. The first step occurs at 127, 130, 134 and 135 oC (when R = I, OMe, NO2, N2Ph) respectively corresponding to the loss of two water molecules. The second step occurs at 210, 231, 235, 218 oC corresponding to the loss of organic ligand moiety. The compound (when R = NO2) has got the highest thermal stability. The Schiff base is more potent antibacterial than the compounds. The antibacterial data indicate high activity of the ligand (when R = I) against S. pyogenes, S. agalaciae, S. aureus, P. anthracis, K. pneumoniae and P. aeruginosa.

D. With pentadentate ligands: Relatively little work has been reported on Fe(III) coordination compounds with

pentadentate ligands. A six-coordinate compound, [FeCl(LH)]2H2O (where Na2LH = 62) has been synthesized by stirring a MeOH solution of Na2LH and FeCl36H2O in 1:1 molar ratio for 1 h at room temperature[35]. It is air-stable and insoluble in H2O, EtOH, C6H6,

Me2CO, MeCN, Et2O, py, DMF and DMSO. The energy difference ( = 240 cm-1) between as(COO) and s(COO) stretches suggests the monodentate coordinating

18

behaviour of carboxylato group. Na2HL behaves as a dibasic pentadentate ONOON donor ligand. The non-coordinated H2O molecules are lost between 80-110 oC. The magnetic moment of the compound is 5.9 B.M. The latter shows higher bactericidal activity than Na2LH against P. mirabilis however, it is less active than Na2LH against E. coli, S. aureus, S. enteritidis and S. sonnei. An octahedral structure (77) has been assigned to it. E. With hexadentate ligands:

Tweedle et al.[47] have synthesized a monomeric, six-coordinate, 1:1 electrolyte,

[Fe(LH2)]Y (here LH4 = 78, R = H, OMe, NO2; Y = PF6, NO3, BF4, I, Cl). LH4 acts as a dibasic hexadentate ONNNNO donor ligand. A distorted octahedral geometry has been suggested for the compounds.

Kannappan et al.[48] have synthesized the monomeric, low-spin, six-coordinate

compounds, [FeL](ClO4), [FeL'](ClO4), [FeL](BF4) and [FeL'](BF4) (here LH2 = N,N',N'',N'''-1,5,8,12-tetraazadodecanebis(salicylaldiminato) and L'H2 = N,N',N'',N'''-1,5,8,12-tetraazadodecanebis(3-methoxysalicylaldiminato). LH2 and L'H2 act as the dibasic hexadentate ONNONN donor ligands. The coordination geometry around Fe(III) ion is distorted octahedral with the iron to phenoxo O bonds being trans to each other. In the crystal lattice, the mononuclear entities are organized into infinite 1D chains due to H-bonding interactions involving the secondary amine residue and one O or F atom of a counter anion respectively.

Sarkar et al.[49] have reported the synthesis of a monomeric, six-coordinate, 1:1 electrolyte, [Fe(LH2)](ClO4) [here LH4 = 79]. LH4 acts as a dibasic hexadentate ONSSNO donor ligand.

The syntheses of two monomeric, dark-green, ion-pair coordination compounds,

[FeL][FeCl4] [here LH2 = 1,3-di-(o-salicylaldiminophenylthio)propane] and [FeL'][FeCl4] [here L'H2 = 1,2-di(o-salicylaldiminophenylthio)xylene] have been reported[50]. Each Fe(III) ion has a distorted octahedral geometry in the cationic part and a distorted tetrahedral in the anionic part. The Fe(III) centre in the cationic species is low-spin. Fe(ClO4)36H2O on reacting with above ligands forms the monomeric, six-coordinate, 1:1 electrolyte, [FeL](ClO4) or [FeL'](ClO4) respectively. The Fe(III) centres in both cationic species are high-spin. LH2 and L'H2 act as the dibasic hexadentate N2S2O2 donor ligands.

19

Coordination compounds of cobalt(II) Cobalt (Co) is a hard, grey, d-block transition metal belonging to the Group 9 and

Period IV of the Periodic Table. Its atomic number, atomic weight and electronic

configurations are 27, 58.93 amu and [Ar] 3d74s2 respectively. Its common oxidation states are +2 and +3. The Co(II) has a d7 system and its coordination compounds show the paramagnetism either equivalent to three unpaired electrons (Oh or Td ) or equivalent to one unpaired electron (square-planar). Since the orbital contribution of tetrahedral Co(II) is much less than that of octahedral coordination compounds, the former have generally lower values than octahedral compounds This high degree of orbital contribution for octahedral compounds is due to the three-fold degeneracy of 4T1g ground state. The metal is the central component of the vitamin B12 (cobalmin) and is associated with some proteins such as methionine and aminopeptidase. 60Co is used in radiotherapy. The ability of Co(II) ion to form the coordination compounds with a wide range of ligands is well known. These ligands coordinate to Co(II) ion in a bidentate, tridentate, tetradentate, pentadentate and hexadentate fashion. We present here a brief survey of the Chemistry of

coordination compounds of Co(II) ion. A. With bidentate ligands:

The synthesis of a brown, four-coordinate non-electrolyte (M = 6.9 mho cm2 mol-1), [Co(OAc)L(H2O)] (where LH = 25; R = 3-OMe, R' = OH, R'' = H) has been reported[2]. It decomposes at 270 oC. It is soluble in DMF and DMSO. LH acts as a monobasic bidentate ON donor ligand. The presence of coordinated H2O molecule is indicated by the

presence of a broad band at 3400 cm-1 in the above coordination compound. The acetato ligand is coordinated in a monodentate fashion. It shows the (CoO) and (CoN) vibrations at 510 and 435 cm-1 respectively. The magnetic moment (4.30 B.M.) of the compound indicates a tetrahedral environment around the metal ion.

The synthesis of a green, high-spin, four-coordinate compound, [CoClL(PPh3)] (where LH = 25; R = H, C4H4; R' = OH, R'' = H, Cl, Me, OMe) has been reported[38]. The IR data are indicative of the monobasic bidentate ON donor behaviour of LH. The magnetic moments of the coordination compounds lie between 1.8-2.3 B.M. in square-

planar environment. They have been used as catalysts in aryl-aryl coupling reactions between C6H5MgBr and C6H5Br to yield biphenyl.

20

An EtOH solution of CoCl26H2O and LH (80) on refluxing for 2 h in 1:2 molar ratio, a four-coordinate compound, [CoL2] is obtained[51]. LH acts as a monobasic bidentate ON donor ligand. The magnetic moment (3.58 B.M.) of the compound and the occurrence of a band at 16366 cm-1 due to the 1A1g 1B1g transition support its square-planar geometry. Its antibacterial activity against bacteria like S. aureus, B. subtilis, E. coli and the fungus A. niger is higher than LH.

A MeOH solution of Co(OAc)24H2O and LH3 (81; R = OH, R' = H) or L'H4 (81; R = R' = OH) in 1:2 molar ratio on refluxing for 1 h produce a brown, four-coordinate, non-electrolyte (M = 8.7 mho cm2 mol-1), [Co(LH2)2]3H2O and another red non-electrolyte (M = 7.6 mho cm2 mol-1), [Co(L'H3)2]3H2O respectively[52]. Both the coordination compounds are soluble in DMF, DMSO and THF. The former melts at 295 oC, while the latter at >300 oC. Both the Schiff bases act as monobasic bidentate ON donor ligands. The (CoO) and the (CoN) vibrations occur at 475 and 455 cm-1 in [Co(LH2)2]3H2O, while these occur at 480 and 445 cm-1 in [Co(L'H3)2]3H2O respectively. The magnetic moments of [Co(LH2)2]3H2O and [Co(L'H3)2]3H2O are 4.38 and 4.33 B.M. respectively suggesting their tetrahedral geometries around the metal ion.

Tumer et al.[53] have observed that an EtOH solution of Co(OAc)24H2O and LH2 (82; R = H, R' = 2-OH, R'' = 3-OMe) or L'H (82; R = R' = H, R'' = 4-NMe2) or L''H2 (82; R = 3-CMe3, R' = 4-OH, R'' = 5-CMe3) on refluxing in 1:2 molar ratio produce the compounds, [Co(LH)2]H2O (red-brown), [CoL'2]H2O (dark-red) and [Co(L''H)2]H2O (red) respectively. They are monomeric, air-stable, non-electrolytes and are soluble in common polar solvents. Although LH2 and L''H2 are potentially the dibasic tridentate

ONO donor ligands, but similar to L'H, they also act as the monobasic bidentate ON donor ligands in the respective compounds. The NH and pyridine N atoms do not participate towards the coordination. These tetrahedral coordination compounds have magnetic moments 4.13, 4.23 and 4.50 B.M. respectively.

The brown compound, [CoL2(H2O)2] (here LH = 28) and the reddish-brown compound, [CoL'2(H2O)2] (L'H = 29) have been synthesized by template method[4]. The reaction of 2-aminophenol with Co(II) ions produces the aminophenolate coordination compound as precipitate (in solution), which on further treatment with 4-benzyloxybenzaldehyde or but-2-enal in 1:1:1 molar ratios yields the desired compounds.

21

[CoL2(H2O)2] and [CoL'2(H2O)2] melt at 245 and 225 oC respectively. Both LH and L'H act as monobasic bidentate ON donor ligands. [CoL2(H2O)2] displays the (CoO) and (CoN) vibrations at 596 and 450 cm-1 respectively, while [CoL'2(H2O)2] displays these vibrations at 580 and 460 cm-1 respectively. [CoL2(H2O)2] exhibits two bands, one at 14577 cm-1 and another at 17094 cm-1, while [CoL'2(H2O)2] exhibits these bands at 14815 and 17241 cm-1 respectively due to the 4T1g(F) 4A2g(2) and 4T1g(F) 4T1g(P)(3) transitions respectively indicating the octahedral environment around the metal ion. The

magnetic moments of [CoL2(H2O)2] and [CoL'2(H2O)2] are 4.97 and 4.95 B.M. respectively favouring the presence of three unpaired electrons of Co(II) ion in a high-spin octahedral compound. The higher values than the spin-only value (3.89 B.M.) is due to the orbital contribution. Their biologically activity against S. dysenteria, E. coli, P.

aeruginosa, B. subtilis, S. lutea and S. aureus is more than 2-aminophenol. The monomeric, four-coordinate compound, [CoL2] (here LH = Schiff base

obtained from the condensation of cinnamaldehyde and 2-aminophenol) has been synthesized by refluxing an EtOH solution of Co(OAc)24H2O and LH in 1:2 molar ratio[54]. LH acts as a monobasic bidentate ON donor ligand. The magnetic moment of the compound is 5.50 B.M. A tetrahedral structure has been assigned to it.

The blue, six-coordinate compound, [Co(LH)2(H2O)2] (83; M = Co, Y = O, COO) has been synthesized[55] by refluxing a MeOH solution of LH2 [here LH2 = Schiff base obtained from the condensation of 1,2,3,5,6,7,8,8a-octahydro-3-oxo-N-1-diphenyl-5-(phenylmethylene)-2-naphthalenecarboxamide and 2-aminophenol/2-aminobenzoic acid] and Co(OAc)24H2O in 1:2 molar ratio for 2 h followed by adjusting the pH to 7.0 using 3% NaOH solution. It is soluble in DMF and DMSO, partially soluble in MeCN and

CHCl3 but insoluble in H2O. The complete loss of coordinated water molecules occurs at 130 oC. The IR data are indicative of the monobasic bidentate ON donor behaviour of the Schiff base. The carboxylato group is coordinated in a monodentate fashion. The compound (when Y = O) shows two intense bands one at 13900 cm-1 and another at 18800 cm-1 due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P) transitions in an octahedral environment. These bands occur at 14100 and 18900 cm-1 in the compound (when Y = COO) respectively. Their magnetic moments (4.86 and 3.18 B.M., when Y = O, COO

22

respectively) indicate a high-spin octahedral environment around Co(II) ion. A trans-octahedral structure (83; M = Co, Y = O, COO) has been suggested for them.

A light-brown, four-coordinate, polystyrene-anchored coordination compound,

[PSCH2L(OAc)Co(DMF)] (here PSCH2LH = 68) has been synthesized by refluxing Co(OAc)24H2O and PSCH2LH in 2:1 molar ratio in N2 atmosphere[25]. The PRC of the compound is 34.6. The MBC of the ligand is 0.53 mmol of metal per g of it. The coordinated DMF molecules are coordinated to the metal ion through O atom. The acetato

ligand is coordinated in a monodentate fashion. The Schiff base acts as a monobasic bidentate ON donor ligand. The magnetic moment (2.40 B.M.) of the compound suggests a square-planar geometry around the metal ion.

A four-coordinate, non-electrolyte, [Co2(OH)(Cl)(LH)2]H2O (where LH2 = 32) has been synthesized[8] by mixing CoCl26H2O and LH2 in the presence of Et3N. The ligand coordinates in a monobasic bidentate ON donor fashion. The magnetic moment of the compound is 3.4 B.M. A tetrahedral structure has been assigned to it.

A violet, six-coordinate, non-electrolyte (M = 10.6 mho cm2 mol-1 in DMSO), [CoCl2(LH2)2] (here LH2 = 84; R = 4-OH, R' = Me) is obtained by refluxing an H2O/EtOH solution of CoCl26H2O and LH2 in 1:1 molar ratio for 8 h[56]. It is insoluble in Me2CO, CHCl3 and C6H6 but is fairly soluble in DMF and DMSO. It decomposes between 245-247 oC. LH2 acts as a neutral bidentate ON donor ligand. The coordination compound displays two bands one at 16338 cm-1 and other at 19330 cm-1 due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P)(3) transitions. The spectral parameters [10Dq (8602 cm-1), B' (860 cm-1), (0.88), 0 (11.4), LFSE (81.9 kJ mol-1)] and the magnetic moment (5.16 B.M.) support its octahedral geometry. The latter shows higher antibacterial activity against E. coli than LH2, whereas its antifungal activity against A. niger is less than LH2. An octahedral structure (85, M = Co) has been assigned to the compound.

Although, LH2 (86) is potentially a dibasic pentadentate O2N3 ligand, it acts as a monobasic bidentate ligand[57] in the brown, six-coordinate compound, [Co(OAc)(LH)(H2O)2]. The bonding takes place through the enolic O and the azomethine N atoms. The acetato group is coordinated in a bidentate fashion. The OH and NH2 groups

do not participate in the coordination. The magnetic moment (4.71 B.M.) and the appearance of two bands (17360 and 20964 cm-1) suggest its high-spin octahedral

23

geometry. The ligand has been used for the micro-determination of Co(II) ion within metal concentration up to 46.3 ppm.

An EtOH solution of Co(OAc)24H2O and LH2 (30, R = H) in 1:2 molar ratio upon refluxing in the presence of TEM produce[6] a brown-red compound, [Co(LH)2]. It is non-electrolyte (M = 16 mho cm2 mol-1) and decomposes at 268 oC. LH2 acts as a monobasic bidentate ON donor ligand.

An EtOH solution of LH2 (87; R = H, 5,6-benzo) reacts with a warmed EtOH solution of CoCl26H2O in 1:1 molar ratio at pH ~7 and forms[58] the six-coordinate, non-electrolyte, dinuclear compound, [Co2L2(H2O)4]. It is pink (when R = H) and red (when R = 5,6-benzo). They are amorphous in nature, having high melting points and are feebly soluble in DMF and dioxane. The IR data are indicative of the monobasic bidentate ON donor nature of the ligand per metal ion coordinating through its phenolic O and

azomethine N atoms. The as(O==S==O) and the s(O==S==O) stretches of LH2 occurring at 1150-1155 and 1320-1330 cm-1 respectively remain at the same energy in the coordination compounds indicating the non-involvement of sulphone O atom(s) towards coordination. The (CoO) and the (CoN) vibrations occur at 500, 355 and 505, 350 cm-1 (when R = H, 5,6-benzo respectively). They display the absorption bands at ~8955, ~18125, ~20800 and 32500 cm-1 due to the 4T1g(F) 4T2g(F)(1), 4T1g(F) 4A2g(F)(2), 4T1g(F) 4T1g(P)(3) and charge transfer transitions respectively indicating the octahedral environment around the metal ion. The spectral parameters: [10Dq (9170, 8775 cm-1), B' (809.3, 795.1 cm-1), 2/1 (2.02. 2.00), (0.883, 0.81) and (20.48, 23.45)] further lend support for their octahedral geometry. Their sub-normal magnetic moments (2.7 and 2.6 B.M.) indicate MM interactions in a polymeric structure. The unpaired electron of the d-orbital of the metal ion overlaps with the -orbital of the N atom of the azomethine moiety of the ligands. Due to the high electron density of the N atoms, an electron from N

moves to partially occupied d-orbital of the metal ion with antiparallel spin to the original d-electron. Thus, the magnetic moments are aligned antiparallel and are responsible for partial quenching of paramagnetism due to the super-exchange phenomenon. A dinuclear, octahedral structure (88, R = H, 5,6-benzo; M = Co, A = H2O) has been suggested to it.

Chohan et al.[59]

have observed that on refluxing an EtOH solution of CoCl26H2O and an H2O/EtOH solution of cloxacillin (NaLH, 89) in 1:1 and 1:2 molar ratios, air and

24

moisture-stable, intense-coloured, amorphous, six-coordinate compounds, [CoCl(LH)(H2O)3] and [Co(LH)2(H2O)2] respectively are obtained. They are insoluble in common organic solvents and soluble in H2O, DMF and DMSO. NaLH behaves as a

monobasic bidentate ON donor (carboxylic O and endocyclic N of -lactam ring) ligand. The carboxylato group is coordinated in a monodentate mode. The presence of the (CoO) stretch at 525 cm-1 and (CoN) stretch at 410 cm-1 indicates the bonding through O and N atoms. The presence of the (CoCl) stretch in the former at 320 cm-1 supports the presence of coordinated chloro group to the metal ion. The former shows the 4T1g(F) 4T2g(F), 4T1g(F) 4A2g(F) and 4T1g(F) 4T2g(P) transitions at 7375, 17280 and 20595 cm-1 and the latter at 7225, 17165 and 20380 cm-1 respectively, for octahedral configuration.

They show antibacterial activities against E. coli, K. pneumoniae, P. mirabilis, P.

aeruginosa, S. typhi, S. dysentriae, B. cereus, C. diphtheriae, S. pyogenes and S. aureous. The structures, 90 (M = Co) for [CoCl(LH)(H2O)3] and 91 (M = Co) for [Co(LH)2(H2O)2] have been assigned.

Amirnasr et al.[60] have synthesized a four-coordinate compound, [CoX2L] [here L = N,N'-bis(-phenylcinnamaldehyde)-1,2-diaminoethane, X = Cl, Br] by refluxing CoX26H2O and L in CH2Cl2 in 1:1 molar ratio under N2 atmosphere. It has a distorted tetrahedral structure.

Upon refluxing an EtOH solution of CoCl26H2O and LH2 (92) in 1:2 molar ratio for 1 h at pH = 6, a six-coordinate compound, [Co(LH)2(H2O)2] is obtained[61]. It is soluble in common organic solvents. It is non-electrolyte (M = 11.5 mho cm2 mol-1) in Me2CO. The (CoN) vibrations occur at 440 cm-1. The Schiff base acts as a bidentate NN donor ligand. The appearance of two spin-allowed transitions at 17856 and 21734 cm-1 due to the 4T1g(F) 4A2g(F) and 4T1g(F) 4T1g(P) transitions respectively and the value of magnetic moment (4.81 B.M.) suggest the high-spin, distorted octahedral geometry around the metal ion.

The synthesis of a bluish-green, six-coordinate, non-electrolyte, [Co(LH)2(H2O)2] (83; M = Co, Y = S) has been reported[55]. It is soluble in DMF and DMSO, partially soluble in MeCN and CHCl3 but insoluble in H2O. The complete loss of the coordinated

H2O molecules occurs at 130 oC. The IR data are indicative of the monobasic bidentate NS donor behaviour of the Schiff base. The appearance of two intense bands (14000 and

25

19000 cm-1) due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P) transitions respectively and the magnetic moment (4.90 B.M.) suggest an octahedral environment around the metal ion.

B. With tridentate ligands: Sallam et al.[62] have reported the synthesis of a yellow coordination compound,

[Co(LH)2]2H2O [where LH2 = 93; R' = R'' = Ph, A = (CH2)2] and two brown compounds, [Co(L'H)2]H2O [here L'H2 = 93; R' = Ph, R'' = Me, A = (CH2)2] and [Co(L''H)(OH)] [here L''H2 = 93; R' = R'' = Me, A = (CH2)2]. They are insoluble in EtOH, Me2CO, C6H6, CHCl3 and partially soluble in DMF and DMSO. They are non-electrolytes (M = 7.7-9.0 mho cm2 mol-1) in DMSO. The IR data are indicative of the monobasic tridentate ONO donor behaviour of these Schiff bases. The (CoO) and the (CoN) vibrations occur between 519-659 cm-1 and 394-565 cm-1. The octahedral compounds, [Co(LH)2]2H2O and [Co(L'H)2]H2O exhibit three bands at 17667, 19880 and 22222; 18587, 20833 and 23752 cm-1 due to the 4T1g(F) 4A2g(F) and 4T1g(F) 4T1g(P) and intra-ligand transitions respectively. The appearance of a band at 18691 cm-1 due to the 4A2 4T2(F) transition in [Co(L''H)(OH)] suggests its tetrahedral structure. The magnetic moments of [Co(LH)2]2H2O and [Co(L'H)2]H2O are 5.3 and 5.2 B.M. respectively indicating the presence of high-spin six-coordinate geometry around the metal ion. The magnetic moment (3.2 B.M.) of [Co(L''H)(OH)] is intermediate between the values for tetrahedral and square-planar structures and results from a spin-equilibrium between low- and high-spin states. [Co(L'H)2]H2O has an endothermic peak between 46-130 oC indicating the loss of lattice water molecule. The existence of two exothermic peaks between 156-260 and 370-480 oC indicates the loss of side chain and ligand moieties respectively. CoO is the final product formed.

A brown, monomeric, six-coordinate, polystyrene-anchored coordination

compound, [PSLCo(DMF)3] (where PSLH2 = 31) is obtained by refluxing a DMF swollen suspension of PSLH2 and Co(OAc)24H2O in 1:2 molar ratio for 8 h[7]. The PRC of the compound is 68.5. The MBC of the ligand is 0.53 mmol of metal per g of it. The Schiff base acts as a dibasic tridentate ONO donor ligand. DMF molecules are coordinated

to the metal ion. The magnetic moment (4.80 B.M.) and the appearance of three bands at 8300, 12500 and 17860 cm-1 due to the 4T1g 4T2g(1), 4T1g 4A2g(2) and 4T1g(F)

26

4T1g(P)(3) spin-allowed transitions respectively suggest an octahedral environment around the metal ion.

Sallam et al.[62] have also reported the syntheses of two brown, four-coordinate

compounds, [Co(OH)(LH)] (where LH2 = 93; R' = R'' = Ph, A = 1,2-C6H4) and [Co(OH)(L'H)] (here L'H2 = 93; R' = CF3, R'' = thienyl, A = 1,2-C6H4). They are non-electrolytes (M = 7.3-9.6 mho cm2 mol-1) in DMSO. The IR data are indicative of the monobasic tridentate ONO donor behaviour of these Schiff bases. The (C==S) stretch (1264 cm-1) of L'H2 remains at the same energy in [Co(OH)(L'H)] indicating the non-coordinating behaviour of S atom of thienyl moiety. The (CoO) and the (CoN) vibrations occur between 647-687 cm-1 and 536-580 cm-1. The appearance of two bands at 12269, 16000 and 11111, 16313 cm-1 due to the 2B2g 2Eg and 2B2g 2Ag in [Co(OH)(LH)] and [Co(OH)(L'H)] respectively is indicative of their square-planar geometry. The magnetic moments of [Co(OH)(LH)] and [Co(OH)(L'H)] are 1.74 and 1.89 B.M. respectively indicating a low-spin square-planar geometry around the metal ion.

Emara et al.[41] have synthesized a yellowish-blue, four-coordinate compound, [Co2L(MeOH)2]2MeOH (where LH4 = 70, X = OH) by refluxing a MeOH solution of LH4 and Co(NO3)26H2O in 1:2 molar ratio for 3 h. It is soluble in common organic solvents but partially soluble in DMF and DMSO. The (C==N)(azomethine) stretch of the ligand occurring at 1642 cm-1 shifts to lower energy by 12 cm-1 in the compound. The IR data are indicative of bis(dibasic tridentate) ONO donor nature of LH4. The (CoO) and the (CoN) vibrations occur at 608 and 524 cm-1 respectively. The magnetic moment (4.41 B.M.) and the appearance of three bands at 21834, 20450 and 16420 cm-1 due to the 4A2(F) 4T2(F), 4A2(F) 4T1(F) and 4A2(F) 4T1(P) transitions in the compound suggest the tetrahedral environment around the metal ion. Both the uncoordinated and coordinated MeOH molecules are lost by heating the coordination

compound between 35-85 and 85-127 oC respectively. Tuncel et al.[63] have synthesized a brown, four-coordinate compound, [CoL(H2O)]

(where Na2LH2 = 94, R = H) and another black, four-coordinate compound, [CoL'(H2O)] (here Na2L'H2 = 94, R = 3-OMe) by refluxing an EtOH solution of CoCl26H2O and an aqueous solution of LH2 or L'H2 respectively in 1:1 molar ratio. They are soluble in DMF,

DMSO. They are non-electrolytes (M = 15.3 and 13.3 mho cm2 mol-1) in aqueous

27

solution and melt at 203 and 245 oC respectively. The IR data indicate a dibasic tridentate ONO donor behaviour of the ligands. Their magnetic moments (3.8 and 3.3 B.M. respectively) indicate a tetrahedral environment around the metal ion. [CoL(H2O)] remains stable up to 130 oC. The loss of coordinated H2O molecule and the decomposition of organic skeleton occur between 130-190 oC and 341-585 oC respectively. In case of [CoL'(H2O)], the above phenomena occurs between 120-185 oC and 338-557 oC respectively. In both the cases, Co3O4 is the final product.

The synthesis of a four-coordinate, high-spin compound, [Co(LH3)(H2O)]nH2O (where LH5 = 95; R = H, Cl) has been reported[64]. Although the Schiff base is potentially a pentabasic heptadentate ligand, but acts as a dibasic tridentate ONO donor ligand. A tetrahedral structure has been suggested for the coordination compound.

An EtOH solution of CoCl26H2O and LH2 [96; R = 3-OMe, R' = OH, R'' = H, R''' = Me] on stirring forms[65] a light-brown, non-electrolyte, air-stable, four-coordinate compound, [CoL(H2O)]. The Schiff base coordinates through its phenolic O, azomethine N and carboxylato O atoms. The band at 16103 cm-1 due to the 4A2 4T1(F) transition indicates a tetrahedral environment around the metal ion. The compound shows the

ferromagnetic behavior. The syntheses of a dark-brown compound, [Co(NO3)(LH)(H2O)2]2H2O and

another violet compound, [Co2(OAc)2L(H2O)]2H2O (where LH2 = 32) have been reported[8]. Both the coordination compounds are non-electrolytes. The ligand is coordinated in a monobasic tridentate ONO donor fashion. The nitrato group is

coordinated as a monodentate mode in the dark-brown compound, whereas, the acetato group is coordinated as a monodentate mode as well as bridged-bidentate ligand in the violet compound. The magnetic moments of the dark-brown and the violet compounds are 4.1 and 2.9 B.M. indicating their high-spin octahedral and tetrahedral geometries

respectively. The occurrence of a band at 16667 cm-1 due to the 4T1g(P) 4A2g transition in the former and the appearance of two bands one at 18018 cm-1 and other at 15385 cm-1

due to the 4T1g(F) 4A2g(F) and 4T1g 4T2g(F) transitions in the latter also indicate the same.

Kumar et al.[10] have reported the synthesis of a brown, six-coordinate, polystyrene-anchored compound, [PSCH2LHCo(DMF)3] (where PSCH2LH3 = 34). The

28

PRC of the compound is 35.4 and the MBC of PSCH2LH3 is 0.22 mmol of Co per g of the ligand. PSCH2LH3 behaves as a dibasic tridentate ONO donor ligand. The magnetic moment (4.89 B.M.) and the appearance of three bands at 9100, 13000 and 18800 cm-1 due to the 4T1g 4T2g(1), 4T1g 4A2g(2) and 4T1g(F) 4T1g(P)(3) spin-allowed transitions respectively are indicative of an octahedral environment around the metal ion.

A brown, six-coordinate, binuclear compound, [Co2L2(H2O)4] [where LH2 = 35A-35C] is obtained by stirring an EtOH solution of Co(OAc)24H2O and LH2 in 1:2 molar ratio for 12 h[11]. It melts at 150 oC. It is soluble in most common solvents except ether. The ligand acts as a dibasic tridentate OON donor ligand. An octahedral geometry [36; M = Co, A = H2O] has been suggested for it.

The air-stable, non-hygroscopic, non-electrolyte, dimeric, six-coordinate

compounds, [CoClL(H2O)]2 (here LH = 43; R = Me, Et, propyl) and [CoCl(L'H)(H2O)]2 (here L'H2 = 43; R = CH2CH2OH) have been synthesized by refluxing a MeOH solution of CoCl26H2O and LH or L'H2 in 1:1 molar ratio for 4 h[16]. They are soluble in DMF and DMSO. The coordinated water molecules are lost between 190-200 oC. Although L'H2 is potentially a dibasic tetradentate NONO donor ligand but similar to LH, it also behaves as a monobasic tridentate NON donor ligand bridging through its enolic O atom. The coordination compounds display three bands between 10952-10989, 16806-16949 and 23584 cm-1 due to the 4T1g(F) 4T2g(F)(1), 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P)(3) transitions respectively indicating the octahedral environment around the metal ion. The magnetic moment (4.54-4.70 B.M.) support the weak anti-ferromagnetic spin-exchange interaction between the two Co(II) ions. They exhibit higher antifungal activity against A. niger than the corresponding ligands. A distorted octahedral structure (44; M = Co) has been suggested for them.

A violet, nano-crystalline, four-coordinate compound, [CoL(H2O)]Cl (where LH = 97) has been synthesized by refluxing a MeOH solution of CoCl2xH2O and LH in 1:1 molar ratio for 2 h[66]. The complex is 1:1 electrolyte (M = 85 mho cm2 mol-1 in MeOH). It is soluble in DMF and DMSO. The ligand behaves as a monobasic tridentate NON donor coordinating through its azomethine N, carboxylato O and imidazole N atoms. The

magnetic moment (4.21 B.M.) and the existence of a band at 17857 cm-1 due to the 4A2(F) 4T1(P) transition indicate a tetrahedral environment around the metal ion. The loss of

29

coordinated H2O molecule, Cl- ion (as HCl gas) and the organic skeleton occur between 210-230, 250-270 and 400-550 oC respectively. Finally CoO is obtained as residue.

A brown, six-coordinate compound, [CoL2] (here LH = 45) is obtained[17] on refluxing an hot MeOH solution of Co(NO3)26H2O and LH in 1:2 molar ratio at pH = 7.5-8.5. The compound is non-electrolyte (M = 15.03 mho cm2 mol-1 in DMSO). LH acts as a monobasic tridentate ONN donor ligand coordinating through its phenolic O and both azomethine N atoms. The magnetic moment (4.7 B.M.) and the appearance of three bands at 10162, 18621 and 25575 cm-1 due to the 4T1g(F) 4T1g(P), 4T1g(F) 4A2g and 4T1g(F) 4T1g transitions respectively indicate the presence of high-spin octahedral environment around the metal ions. The compound crystallizes in a monoclinic fashion with a = 16.038 , b =4.285 and c = 10.692 . The compound shows low antimicrobial activity against E. coli than S. aureus, however, it shows moderate antimicrobial activity against E. coli

than S. aureus.

The synthesis of a brown, trinuclear compound, [Co3(NO3)2L2(H2O)2]2H2O (LH2 = 70; X = NH2) has been reported[41]. It is soluble in common organic solvents but partially soluble in DMF and DMSO. The IR data are indicative of bis(monobasic tridentate) ONN donor nature of LH2. The appearance of four new bands at 1548, 1384, 1302 and 1058 cm-1 indicates the presence of bidentate nitrato group in the compound. The (CoO) and the (CoN) vibrations occur at 606 and 542 cm-1 respectively. The magnetic moment (3.20 B.M.) and the appearance of one band at 18868 cm-1 due to the 4T1g 4T2g transition suggest the low-spin octahedral environment around the metal ion.

A yellowish, four-coordinate, non-electrolyte, [CoL(H2O)] (where LH = 98) has been synthesized[67]. It is soluble in DMSO. The monobasic tridentate Schiff base coordinates through its carboxylate O, azomethine N and amino N atoms. The magnetic moment of the compound is 4.61 B.M. The appearance of a band at 22026 cm-1 due to the 4A2 4T1(P) transition indicates the tetrahedral geometry around the metal ion. The compound crystallizes in a monoclinic fashion.

A purple, six-coordinate, non-electrolyte (M = 9.9 mho cm2 mol-1 in DMSO), [CoCl2(LH)(H2O)]n (here LH = 84; R = H, R' = Me) has been synthesized by refluxing an H2O/EtOH solution of CoCl26H2O and LH in 1:1 molar ratio for 1 h[56]. The compound is insoluble in Me2CO, CHCl3 and C6H6 but is fairly soluble in DMF and DMSO. It melts

30

between 240-242 oC. The coordinated H2O molecule is lost at 130 oC. LH acts as a neutral tridentate ONN donor ligand. The compound displays two bands one at 16130 cm-1 and other at 19230 cm-1 due to the 4T1g(F) 4A2g(F)(2) and 4T1g(F) 4T1g(P)(3) transitions respectively. The spectral parameters [10Dq (8558 cm-1), B' (855 cm-1), (0.88), 0 (11.9%) and LFSE (81.4 kJ mol-1)] and the magnetic moment (4.96 B.M.) lend support for its octahedral geometry. The compound shows higher antibacterial activity against E. coli than LH, whereas its antifungal activity against A. niger is less than LH. An

octahedral polymeric structure (99, M = Co) has been assigned to the compound. The synthesis of a green, monomeric, four-coordinate compound,

[Co(LH)(H2O)]Cl (where LH2 = 86) has been reported[57]. The ligand is linked through its enolic O, azomethine N and amino N atoms. The phenolic OH group does not participate

in the coordination. The magnetic moment (4.42 B.M.) and the occurrence of two bands at 14749 and 20921 cm-1 suggest a tetrahedral geometry of the compound.

Sebastian et al.[20] have observed that the complexation of the yellow coloured Schiff base, (LH2 = 46A, 46B) with Co(II) ion proceeds with the rearrangement of benzothiazoline ring to form the corresponding brown colored, non-electrolyte, [CoL(H2O)3]H2O. The Schiff base coordinates in enolic form as dibasic tridentate ONS donor ligand. The magnetic moment (5.18 B. M.) suggests a high-spin octahedral geometry for the complex. The lattice water molecule and three coordinated water

molecules are lost between 90-120 oC and 150-200 oC respectively. A brown, mononuclear, six-coordinate compound, [Co(LH2)(H2O)3] (where LH4 =

100) has been synthesized[42]. The Schiff base behaves as a dibasic tridentate ONS donor ligand coordinating through its enolic O, azomethine N and thiolato S atoms. The oxime

group does not participate in coordination. A pink, non-electrolyte, [CoL(H2O)2]2, (where LH2 = 47) has been synthesized[21].

The Schiff base acts as a dibasic tridentate ONS donor ligand. The bands at 8728 and

19200 cm-1 due to the 4T1g 4T2g(F) and 4T1g 4T1g(P) transitions respectively and the magnetic moment (4.86 B.M.) are indicative of the octahedral environment around the metal ion. Here two cobalt ions are bridged through phenolic O atoms resulting in a dimer.

An aqueous solution of Co(OAc)24H2O reacts[22] with an EtOH solution of LH2 (48) in 1:2 molar ratio in N2 atmosphere and forms an air-stable, reddish-brown

31

compound, [Co(LH)2]. It decomposes at 186 oC and is soluble in Me2CO, DMF and DMSO. It is non-electrolyte (M = 12.3 mho cm2 mol-1 in DMSO and 3.1 mho cm2 mol-1 in Me2CO). The Schiff base acts as a monobasic tridentate ONS donor ligand and coordinates to the metal ion through its hydroxylic O, azomethine N and thiolato S atoms.

The (CoN) vibrations occur at 565 cm-1 in the compound. The magnetic moment (4.9 B.M.), the appearance of a broad band (7700 cm-1) and two shoulders (13500 and 20500 cm-1) due to the 4T1g 4T2g(1), 4T1g 4A2g(2) and 4T1g 4T1g(P)(3) transitions respectively indicate the presence of high-spin octahedral environment around the metal

ion. A distorted octahedral structure, 49 (M = Co) has been suggested for it. An air-stable, four-coordinate compound, [CoCl(LH)]3H2O (here LH2 = 37) has

been obtained by stirring a MeOH solution of LH2 and CoCl26H2O in 2:1 ratio at pH 8.0 for 8 h[68]. It is soluble in DMSO and DMF, slightly soluble in MeCN and insoluble in

MeOH and H2O. It behaves as non-electrolyte in DMSO. It shows a mass loss equivalent to three H2O molecules in the 90-110 oC range, suggesting that these molecules are not coordinated to the metal ion. The carboxylato group is coordinated in a monodentate mode. The low value of the magnetic moment (4.1 B.M) of the compound indicates its distorted tetrahedral geometry.

The synthesis of an air-stable, four-coordinate compound, [CoCl(LH)]2H2O (here LH2 = 39) has been reported[13]. The compound is soluble in DMSO and DMF and slightly soluble in MeCN. It exhibits the non-electrolytic behavior in DMSO. NaLH behaves as a monobasic tridentate OON donor ligand. The carboxylato group is coordinated in a

monodentate fashion. The (CoN) stretch occurs at 450 cm-1. The compound shows a broad band centered at 25640 cm-1 due to Td symmetry around the metal ion. Its magnetic moment is 3.8 B.M. The compound shows higher activity than NaLH against P. mirabilis, K. pneumoniae, S. enteriditis and E. coli, while it remains inactive towards S. aureus and

P. aeruginosa. A tetrahedral structure (40, M = Co) has been assigned to it. A four-coordinate compound, [CoCl(LH)] (here LH2 = 50; R = OMe, R' =

NH2) has been synthesized by stirring a MeOH solution of NaLH and CoCl2.6H2O in 2:1 molar ratio for 8 h at room temperature[43]. It is air-stable and soluble in DMF and

DMSO and is slightly soluble in MeCN. It is non-electrolyte in DMSO. The carboxylato group is coordinated in a monodentate fashion. The presence of the (CoS) stretch at

32

300 cm-1 indicates the coordination through S atom of thiophene moiety. LH2 behaves as a monobasic tridentate OOS donor. The magnetic moment of the compound is 4.2 B.M. The compound is inactive towards S. aureus, E. faecalis, E. coli and P. mirabilis, while it shows lesser antibactericidal activity than the ligand against S. sonnei and S. enteritidis. A distorted tetrahedral structure (51; R = OMe, R' = NH2, A = nil; M = Co) has been assigned to it.

Suni et al.[69] have noticed that upon refluxing an EtOH solution of

Co(OAc)24H2O, LH (52; R = (C5H4N)2C, R' = NHC6H11, X = S) and KSCN in 1:1:1 molar ratios, a brown, four-coordinate compound, [Co(NCS)L]2H2O is obtained. On the other hand, on refluxing an EtOH solution of CoCl26H2O and L'H (52; R = (C5H4N)2C, R' = NHC6H5, X = S) in 1:1 molar ratio, another brown, four-coordinate compound, [CoClL']2H2O is obtained. Both the ligands behave as the monobasic tridentate NNS do