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Synthesis, Physico-Chemical and Biological Properties of Complexes of Cobalt(II) Derived from Hydrazones of Isonicotinic Acid Hydrazide
Synthesis, Physico-Chemical and Biological Properties of Complexes of Cobalt(II) Derived from Hydrazones of Isonicotinic Acid Hydrazide
Journal of the Korean Chemical Society. 2009. Feb, 53(1): 17-26
Copyright © 2009, The Korean Chemical Society
  • Received : July 15, 2008
  • Published : February 20, 2009
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About the Authors
Surendra Prasad
School of Chemical Sciences, Faculty of Science and Technology, The University of South Pacific, Suva, Fiji
prasad_su@usp.ac.fj
Ram K. Agarwal
Department of Chemistry, Lajpat Rai Postgraduate College, Sahibabad, Ghaziabad 201005, India
prasad_su@usp.ac.fj

Abstract
Hydrazones of isonicotinic acid hydrazide, viz., N-isonicotinamido-furfuralaldimine (INH-FFL), N-isonicotnamido-cinnamalidine (INH-CIN) and N-isonicotnamido-3',4',5'-trimethoxybenzaldimine (INH-TMB) were prepared by reacting isonicotinic acid hydrazide with respective aromatic aldehydes, i.e. , furfural, cinnamaldehyde or 3,4,5-trimethoxy-benzaldehyde. A new series of fifteen complexes of cobalt(II) with these new hydrazones, INH-FFL, INH-CIN and INH-TMB, were synthesized by their reaction with cobalt(II) salts. The infrared spectral data reveal that hydrazone ligands behave as a bidentate ligand with N, O donor sequence towards the Co 2+ ion. The complexes were characterized on the basis of elemental analysis, magnetic susceptibility, conductivity, infrared and electronic spectral measurements. Analytical data reveal that the complexes have general composition [Co(L) 2 X 2 ] and [Co(L) 3 ](ClO 4 ) 2 where L= INH-FFL, INH-CIN or INH-TMB and X = Cl , NO 3 , NCS or CH 3 COO . The thermal behaviour of the complexes were studied using thermogravimetrictechnique. Electronic spectral results and magnetic susceptibility measurements are consistent with the adoption of a six-coordinate geometry for the cobalt(II) chelates. The antimicrobial properties of cobalt(II) complexes and few standard drugs have revealed that the complexes have very moderate antibacterial activities.
Keywords
INTRODUCTION
The metal chelates with ligands of biological importance have been playing an important role in the development of new coordination chemistry. Complexes containing chelating ligands, which show promising biological activity, have been recently studied by ourselves 1 - 9 and others. 10 - 20 We have been investigating the synthesis and characterization of cobalt(II), 1 , 2 nickel(II), 2 , 3 oxovanadium(IV) 4 , 5 and platinum(II) 6 and some lanthanide (III) 7 complexes that contain a range of ancillary ligands such as semicarbazones[7], thiosemicarbazones 1 , 2 , 4 - 6 derived from 4-aminoantipyrine and hydrazones 3 derived from isonicotinic acid hydrazide. The antibacterial and antifungal properties of the thiosemicarbazone ligands and their cobalt(II), 1 , 2 nickel(II) 2 and oxovanadium(IV) 4 complexes and nickel(II) complexes with hydrazones 3 have also been examined by us.
Isoniazid (isonicotinic acid hydrazide; INH) is a drug of proven therapeutical importance, used against wide spectrum bacterial ailments, viz. , tuberculosis. Hydrazones derived from condensation of isoniazid with pyridine aldehydes have been found to show better antitubercular activity than isoniazid. 21 We have recently turned our attention to the investigation on transition metal complexes of N and O donor ligands. 3 , 8 , 9 In this paper we report the synthesis, characterization and biological activities of cobalt(II) complexes of hydrazones derived from isonicotinic acid hydrazide viz., N-isonicotinamido-furfural-2'-aldimine (INH-FFL), N-isonicotinamido cinnamalidine (INH-CIN) and N-isonicotinamido-3',4',5'-trimethoxybenzalaldimine(INH-TMB) ( Fig. 1 - 3 ).
. 1
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N-Isonicotinamido-furfuraldimine (INH-FFL)
. 2
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N-Isonicotinamido-3´,4´,5´-trimethoxybenzaldimine(INH-TMB)
. 3
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N-Isonicotinamido-cinnamalidene (INH-CIN)
EXPERIMENTAL SECTION
- Materials
The general experimental techniques have been previously described 3 , 8 . CoX 2 ․nH 2 O (X = Cl , NO 3 or CH 3 COO ) were obtained from BDH and were used without further purification. Co(NCS) 2 was prepared by the reaction of CoCl 2 (in ethanol) and ethanolic solution of KNCS in 1:2 molar ratio. The precipitated KCl was filtered off and the filtrate having Co(NCS) 2 was used immediately for complex formation with hydrazones viz., INH-FFL, INH-CIN and INH-TMB. Co(ClO 4 ) 2 was prepared by the reaction of an ethanolic solution of CoCl 2 and NaClO 4 in 1:2 molar ratio. The white precipitate of NaCl was filtered off and the filtrate containing Co(ClO 4 ) 2 was used as such for complex formation with hydrazones. During the preparation of Co-(NCS) 2 and Co(ClO 4 ) 2 , KNCS and NaClO 4 were taken 10% excess.
- Synthesis of hydrazones: INH-FFL, INH-TMB and INH-CIN
All the three hydrazones of INH viz., INH-FFL, INH-CIN and INH-TMB were synthesized by method reported by us. 3 , 8 , 9 INH (0.01 mol) was dissolved in 10 mL of 95% ethanol. To this solution respective aromatic aldehyde i.e. furfural, cinnamaldehyde or 3,4,5-trimethoxybenzaldehyde (0.01mol) in 95% alcohol (10 mL) was added. The reaction mixture was refluxed on a water bath for ~2 hr. The partial removal of solvent on a water bath followed by cooling produced crystalline product of the complexes, which was suction filtered, washed with cold ethanol and dried under vacuum(yd. ~ 80%).
- Synthesis of cobalt(II) complexes: [CoX2(L)2] and [Co(L)3](ClO4)2
Depending on nature of anionic ligands (Cl , NO 3 , NCS , CH 3 COO or ClO 4 ), the cobalt(II) complexes were synthesized by the reaction of warm ethanolic solution of ligand (INH-FFL, INH-TMB or INH-CIN) and metal salts in 1:2 or 1:3 molar ratio. The reaction mixture was refluxed on a water bath for 2-3 hr. It was then concentrated to a small volume on a hot plate at 50 ℃. On cooling the solutions crystals of complexes appeared which were filtered, washed with ethanol and dried in vacuum over P 4 O 10 (yd. 60-75%).
- Instrumentation, physical, analytical and antimicrobial studies
The cobalt in the complexes was estimated, spectrophotometrically using 2-nitroso-1-naphthol, after decomposing the complex with conc. H 2 SO 4 and H 2 O 2 . 22 The chloro content in the complexes was estimated by Volhard’s method. 22 The thiocyanate was estimated by titrating slightly acidic solution of the complex with standard AgNO 3 solution. The perchlorate was estimated by the methods of Kurz et al. 23 The percentage of nitrogen was determined in the laboratory by Kjeldahl method. The molecular weight of the complexes was determined cryoscopically in freezing PhNO 2 using a Beckmann thermometer of accuracy ± 0.01℃. The conductivity measurements were carried out using a Toshniwal conductivity bridge and dip type cell operated at 220 volts, AC mains. All the measurements were done at room temperature in PhNO 2 as solvent.
The magnetic measurements on powder form of the complexes were carried out at room temperature on Evans magnetic balance (Sherwood Scientific, Cambridge, England) using copper sulphate as calibrant. The infrared spectra of the complexes were recorded on a Perkin Elmer infrared spectrophotometer model 521 in KBr in the range of 4000-200 cm -1 . Diffused reflectance spectra of the solid compounds were recorded on a Beckman DK-2A spectrophotometer. Thermogravimetric analyses of the complexes were carried out at IIT Roorkee, India, on a Perkin Elmer Pyris Diamond thermogravimentric analyzer, in static air with open small platinum boat sample holders using the heating rate of 6 ℃ min -1 . The antibacterial and antifungal activities of some of the representative cobalt(II) complexes and standard drugs (ampicillin and tetracycline) were screened by following the methods reported else where. 1 , 2
RESULTS AND DISCUSSION
The reaction of Co 2+ salts with INH-FFL, INH-CIN or INH-TMB on refluxing afforded the complexes of the general composition Co(L) n X 2 where X = Cl , NO 3 , NCS or CH 3 COO , n = 2 while X = ClO 4 , n = 3 and L = INH-FFL, INH-CIN or INH-TMB. The products were characterized by elemental analysis, magnetic susceptibility, and conductivity, infrared and electronic spectral measurements. The analytical data of these complexes are given in 1 . All the complexes were quite stable and could be stored for months without any appreciable change. The complexes were soluble in common organic solvents such as dichloromethane, acetone, (CH 3 ) 3 SO etc. The complexes do not have sharp melting points but decomposed on heating beyond 250 ℃. The molecular weights determined by cryoscopic method in nitrobenzene are given in 1 . The results are in broad agreement with conductance data. The molar conductance data showed that the chloro, nitrato, isothiocynato and acetato complexes were essentially non-electrolytes in PhNO 2 , while the perchlorato complexes dissociated in PhNO 2 and behaved as 1:2 electrolytes. The magnetic moment data of the complexes reported in 1 show that all the cobalt(II) complexes are paramagnetic corresponding to three unpaired electrons indicating a high-spin octahedral configuration. For the present complexes the magnetic moment values lies in the range 4.6-5.7 BM. 24
Analytical, conductivity, molecular weight and magnetic moment data of Co(II) complexes of hydrazones of isoniazid.
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Analytical, conductivity, molecular weight and magnetic moment data of Co(II) complexes of hydrazones of isoniazid.
- Infrared spectra
A study and comparison of the infrared spectra of all the three ligands, viz. , INH-FFL, INH-TMB and INH-CIN and their Co(II) complexes, imply that all the ligands are bidentate with azomethine nitrogen and carbonyl-oxygen as two (N, O) coordination sites. The infrared data of all the complexes are provided in 2 . The infrared frequencies in the present ligands associated with amide group carbonyl-oxygen (C=O), azomethinenitrogen(C=N) and heterocyclic nitrogen are expected to be influenced on complex formation with metal ion. Generally, all amides show two absorption bands: (i) the carbonyl absorption band near 1640 cm –1 known as amide-I band and (ii) strong band in the 1600-1500 cm –1 region, known as amide-II band. The amide-I band in INH-derivatives, however, appears at 1655 cm –1 . 25 , 26 In the infrared spectra of the complexes, a considerable negative shift in ν(C = O) is observed indicating a decreased in the stretching force constant of C = O as a consequence of coordination through the carbonyl oxygen atom of the free base. The amide-II band appears at the normal position in the NH- deformation rather than C-N link. In all these ligands the absorptions at 1540-1530 cm –1 have been assigned to amide-II absorptions. The NH stretching absorption in free ligands occurs at ~3300 and 3220cm –1 which remain unaffected after complexation. This observation clearly discards any possibility of coordination through imine-nitrogen atom. Another important band occurs in 1590-1585 cm –1 range is attributed to ν(C = N) (azomethine) mode. 27 - 29 In spectra of all the complexes this band shifted to lower wave number and appeared at 1550-1525cm –1 region, respectively indicating the involvement of N-atom of the azomethine group in coordination with Co 2+ ion. 27 - 29 The strong bands observed at 1575-1520 cm –1 and 1080-1000 cm –1 are tentatively assigned to asymmetric and symmetric ν(C = C) + ν(C = N) of pyridine ring 30 , 31 while pyridine ring breathings and deformations remained practically unchanged in frequency and band intensities which clearly revealed non-involvement of pyridine-nitrogen in bonding with Co 2+ ion. In far infrared spectral region, the bands in INH-FFL, INH-TMB and INH-CIN were practically unchanged in these complexes. Some new bonds with medium to weak intensities appeared in the regions 450-380 cm –1 for the complexes under study, which are tentatively assigned to ν(Co-N)/ν(Co-O) modes. 8 , 30 , 31 The overall infrared spectral evidence suggests that the present ligands act as bidentate ligand and coordinate through amide-oxygen and azomethine-nitrogen atoms forming a five membered chelate ring.
Key infrared bands (cm–1) of Co(II) complexes of hydrazones of isoniazid.
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Key infrared bands (cm–1) of Co(II) complexes of hydrazones of isoniazid.
- Anions
The pseudo halide NCS ion is very interesting anion for it may coordinate through the sulfur (thio) or through the nitrogen (isothio) or through both these atoms (bridging). Infrared spectroscopy is very useful in elucidating which type of bonding exists. The various criteria proposed for determining the mode of bonding have been discussed in literature. 31 In general the bonding depends on (a) the nature of central atom (b) the nature of other lignads in the coordination sphere and (c) environmental controls and kinetic (mechanistic) controls. The first transition metal series, i.e. , Class-A metals form M-N type bonds, whereas metals of second and third transition series, i.e. , Class-B metals form the M-S bonds. The C-N stretching frequency (ν 1 ) is generally lower for M-NCS complexes than for M-SCN complexes. Bailey et al. suggested the region near or above 2100 cm –1 for S-bonding below 2100 cm –1 for N-bonding. 32 The C-S stretching frequency (ν 2 ) is assigned in the 860-780 cm –1 region for M-NCS and 720-690 cm –1 for M-SCN bonding modes. 33 , 34 The δ(NCS) frequency (ν 3 ) is also different for the two isomers; 490-450 cm –1 for the M-NCS and 440-400 cm –1 for M-SCN bonding. 33 , 34 Bridging thiocyanate usually give higher CN stretching frequencies than terminal NCS group. 33 , 34 The three fundamental absorption (C-N) stretching (ν 1 ), (C-S) stretch (ν 3 ) and (N-C-S) bending (ν 2 ) in present complexes were identified at 2040-2035, 845-830 and 470-465 cm –1 region respectively. These frequencies are associated with the terminal N-bonded isothiocyanate ions. 33 , 34
In nitrato (NO 3 ) complexes, the infrared spectral data indicate the occurrence of two strong absorption bands in the regions 1555-1500 cm –1 and 1310-1295 cm –1 which are attributed to ν 4 and ν 1 modes of vibrations, of the covalently bonded nitrate groups, respectively. This suggests that nitrate groups are present inside the coordination sphere. 35 Distinction between monodentate and bidentate nitrate is usually different. However, by applying Lever’s separation method, 36 a separation of 15-25 cm –1 in the combination bands (ν 1 4 ) in the 1800-1700 cm –1 region concluded the monodentate nitrate coordination. Other bands appeared at ~1040 (ν 2 ), 810 (ν 6 ) and 7335 cm –1 3 5 ) due to nitrate groups.
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The acetate ion (CH 3 COO ) may coordinate to a metal ion in one of the following modes ( a-c ):
The ν asym (COO ) and ν sym (COO ) of free acetate ion are at ~1560 cm –1 and 1416 cm –1 respectively. In the unidentate complex (structure a ) ν(C = O) is higher than ν asym (COO ) and ν(C-O) is lower than ν asym (COO ). As a result the separation between the two ν(CO) is much larger in unidentate complexes than free CH 3 COO ion. The opposite trend is observed in the bidentate complexes (structure b ) i.e. the separation between two ν(CO) is smaller than that of free CH 3 COO ion in this case. In the bridging complexes (structure c ), however, two ν(CO) are close to the free ion ν(CO) values. The present complexes show infrared absorption frequency bands corresponding to ν asym (COO ) and ν sym (COO ) at ~ 1610 and 1370 cm –1 respectively. These observations indicate that both the acetate groups in present complexes are unidentate. 2 , 37
In all the perchlorato complexes, the presence of the ν 3 (1100-1090 cm –1 ) and ν 4 (625-620 cm –1 ) bands indicates that the tetrahedral symmetry of ClO4 is maintained in all these complexes. Thus it suggested the presence of ClO 4 outside the coordination sphere in these complexes. 17 , 38
- Electronic spectra
The electronic spectra of all the complexes recorded herein consist of three bands; one in the 7800-8772 cm -1 1 ), other in the 15400-15500 (ν 2 ), or 18000-18520 cm -1 2 ), and the third in the 20000-20800 cm -1 3 ), regions, which clearly indicate the octahedral stereochemistry of the complexes. The energy of ν 1 corresponds to 10D q for weak field and the value of D q is obtained from it. All the bands, ν 1 , ν 2 and ν 3 observed are free from shoulders. So the ligand field parameters, D q , B and nephelauxetic effect (β) have been calculated using first order perturbation theory from the ligand field spectra of octahedral Co(II) complexes as discussed by Lever 39 and Reedijk et al. 40 The band maxima, their assignments, the calculated nephelauxetic effect (β) and the ligand field parameters B and D q for some representative chelate complexes are listed in 3 . The appreciable intensity enhancement in all the bands of the Co(II) complexes studied herein clearly shows the existence of distortion from a regular octahedral structure of the present Co(II) complexes. Apart from this, there is no difference in the spectra of regular and pseudo octahedral Co(II) complexes.
Electronic spectral bands (cm–1) and lignad field parameters of Co(II) complex of hydrazones.
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Electronic spectral bands (cm–1) and lignad field parameters of Co(II) complex of hydrazones.
- Thermo gravimetric studies Co(II) complexes of INH-TMB and INH-CIN
The results of the thermo gravimetric studies of [Co(INH-TMB) 2 X 2 ] (X = Cl , NO 3 or NCS ) complexes are presented in 4 . The thrmo gravimetric data indicate that the complexes are stable upto 150 ℃, which indicates that the complexes are non-hygroscopic in nature and does not have any water molecule. The decomposition and deligation process started above 150 ℃. During 180-360 ℃ both the INH-TMB molecules are lost. Finally at ~605 ℃, the cobalt oxide, Co 3 O 4 formation takes place.
Thermoanalytical results obtained for Co(II) complexes of INH‐TMB and INH–CIN.
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Thermoanalytical results obtained for Co(II) complexes of INH‐TMB and INH–CIN.
In case of [Co(INH-CIN) 2 X 2 ] (X = Cl , NCS or CH 3 COO ) complexes the thermo gravimetric curves suggest that in temperature region 190-270℃, the weight loss 37.11-40.26% corresponds to the loss of one molecule of INH-CIN ( 4 ). Further heating the [Co(INH-CIN)X 2 ] complexes at temperature range 280-375 ℃, the weight loss (74.06-80.39%) suggests that second molecule of INH-CIN is also evaporated off. Finally at ~666-610 ℃, Co 3 O 4 is formed. The thermal decomposition of Co(II) complexes studied may be represented by the following equations ( cf. 4 ):
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- Biological studies
The antibacterial activities of the cobalt(II) complexes and standard drugs (ampicillin and tetracycline) were screened by agar-disc method in DMF solvent at a concentration of 50 μg mL -1 . The organisms used in the present investigations included Bacillus subtilis (B.s.) and Staphylococcus aureous (S.a.) as gram positive bacteria and Escherichia coli (E.c.) and Salmonella typhi (S t.) as gram negative bacteria. The zone of inhibition around each disc containing the test compound was measured accurately. The diameters of zone of inhibition (mm) of the standard drug ampicillin against gram positive bacteria Bacillus subtilis and Staphylococcus aureous and gram negative bacteria Escherichia coli and Salmonella typhi were found to be 24, 22, 17 and 16 respectively, while tetracycline gave 18, 17, 21 and 22 respectively. The results of the antibacterial activities are summarised in Table 5 . Under the same conditions, Table 5 shows that all the cobalt(II) complexes of hydrazones studied have moderate antibacterial activities against these bacteria. The cobalt(II) complexes of hydrazones also screened for their antifungal activities against two fungi, Aspergillus niger (A. niger) and Candida albicans (C. albicans) . The results are presented in 5 , which show that almost all the complexes studied showed nearly the same extent of activity but they are less active compared to salicylic acid. These complexes appear to be good antifungal agents.
Antifungal and antibacterial activities of cobalt(II) complexes of INH–FFL and INH–CIN
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Antifungal and antibacterial activities of cobalt(II) complexes of INH–FFL and INH–CIN
CONCLUSION
The present study reveals that the hydrazone ligands, INH-FFL, INH-CIN or INH-TMB act as a neutral bidentate ligand coordinating Co 2+ ion through N, O-donor sites. The overall experimental evidences reveal that the studied Co(II) complexes display a coordination number six and have distorted octahedral structures. The experimental analyses of the chloro, nitrato, thiocyanato and acetato cobalt(II) complexes of INH-FFL, INH-TMB and INH-CIN suggest that the complexes are nonionic in nature while the perchlorato complexes are 1:2 electrolyte and have general composition as [Co(L) 2 X 2 ] and [Co(L) 3 ](ClO 4 ) 2 (X = Cl , NO 3 , NCS or CH 3 COO ; L = INH-FFL, INH-TMB and INH-CIN) respectively.
ACKNOWLEDGMENTS
Acknowledgements
The authors are thankful to URC of the University of the South Pacific for supporting finance for this research through Project Nos. 6395-1321 and 6394-1321 (6C127-1321 and 6C126-1321) and Dr. Abdul Mohammed Hatha, Lecturer, Department of Biology, FST, USP for assisting in studying the biological properties of the compounds.
References
Prasad S , Agarwal R.K. 2007 Trans. Metal Chem. refs. cited therein. 32 143 -    DOI : 10.1007/s11243-006-0119-9
Agarwal R. K. , Prasad S. 2005 Bioinorg. Chem. Appl. refs. cited therein. 3 271 -    DOI : 10.1155/BCA.2005.271
Prasad S , Agarwal R. K. 2008 Res. Lett. Inorg Chem 1 1 -    DOI : 10.1155/2008/350921
Agarwal R. K. , Prasad S. , Gahlot N. 2004 Turk. J. Chem. 28 691 -
Agarwal R. K.; , Prasad S. 2006 Revs. Inorg. Chem. 26 471 -
Agarwal R. K. , Prasad S. 2005 Turkish J. Chem. 29 289 -
Agarwal R. K. , Prakash B. 2005 Trans. Metal Chem. 30 696 -    DOI : 10.1007/s11243-005-5717-4
Agarwal R. K. , Singh L. , Sharma D.K. , Singh R. 2005 Turk. J. Chem. 29 309 -
Agarwal R. K. , Sharma S.K. 1993 Polish J. Chem 67 581 -
Murukan B. , Mohanan K. 2006 Trans. Metal Chem. 31 441 -    DOI : 10.1007/s11243-006-0011-7
Tumer M. , Ekinci D. , Tumer F. , Bulut A. 2007 Spectrochim. Acta A: Mol. Biomol. Spectrosc. 66 1271 -    DOI : 10.1016/j.saa.2006.05.030
Tumer M. , Deligonul N. , Golcu A. , Akgun E. , Dolaz M. 2006 Trans. Metal Chem. 31 1 -    DOI : 10.1007/s11243-005-6249-7
Pandey G. , Narang K.K. 2005 Bioinorg. Chem. Appl. 3 217 -    DOI : 10.1155/BCA.2005.217
Sharaby C.M. 2007 Spectrochim. Acta A: Mol. Biomol. Spectrosc. 66 1271 -    DOI : 10.1016/j.saa.2006.05.030
Mohamed G.C. , Sharaby C.M. 2007 Spectrochim. Acta A: Mol. Biomol. Spectrosc. 66 949 -    DOI : 10.1016/j.saa.2006.04.033
Ashok M. , Prasad A.V.S.S. , Ravinder V. J. 2007 Braz. Chem. Soc. 26 204 -
Ferrari M.B. , Fava G.G. , Leporti E. , Pelosi G. , Tarasconi P. , Albertini R. , Bonati A. , Lunghi P. , Pineli S. 1998 J. Inorg. Biochem. 70 145 -    DOI : 10.1016/S0162-0134(98)10012-0
Srivastava A.K. , Pandey O.P. , Sengupta S.K. 2005 Bioinorg. Chem. Appl. 3 289 -    DOI : 10.1155/BCA.2005.289
Chandra S. , Kumar A. 2007 Spectrochim. Acta A: Mol. Biomol. Spectrosc. 66 1347 -    DOI : 10.1016/j.saa.2006.04.047
Kilpin K.J. , Henderson W. , Nicholson B.K. 2007 Polyhedran 26 204 -    DOI : 10.1016/j.poly.2006.08.009
Sharma R.P. , Kothari A.K. , Sharma N.K. 1995 Ind. J. Derm. Vener. Lepr. 61 261 -
Bassett J. , Denney R.C. , Jeffery G.H. , Mendham J. 1986 Vogel’s Text Book of Quantitative Inorganic Analysis 4th Ed. Longman Sc. Tech. Pub. London
Kurz E. , Kober G. , Berl M. 1958 Anal. Chem. 30 1983 -    DOI : 10.1021/ac60144a030
Agarwal R. K. , Srivastava A. K. , Srivastava M. 1984 Polish J. Chem. 53 393 -
Agarwal R. K. , Sarin R. K. 1993 Polyhedron 12 2411 -    DOI : 10.1016/S0277-5387(00)83061-2
Agarwal R. K. , Sarin R. K. , Agarwal H. 1995 Bull. Chem. Soc. Ethio. 9 23 -
Krishnan P.S.R. , Indrasenan P. 1989 Indian J. Chem. 28A 234 -
Agarwal R.K. , Prakash J. 1991 Polyhedron 10 2399 -    DOI : 10.1016/S0277-5387(00)86201-4
Agarwal R. K. , Dutt P. , Prakash J. 1992 Polish J. Chem. 66 899 -
Burns G.R. 1968 Inorg. Chem. 7 272 -    DOI : 10.1021/ic50060a022
Nakamoto K. 1970 Infrared Spectra of Inorganic and Coordination Compounds Willey New York
Bailey R.A. , Michelson T.W. , Mills W.N. J. 1971 Inorg. Nucl. Chem. 33 3206 -    DOI : 10.1016/0022-1902(71)80097-0
Burmeister J.L. 1966 Coord. Chem. Rev. 1966, 3, 225; 1990, 105, 77. 1 205 -    DOI : 10.1016/S0010-8545(00)80174-5
Bailey R.A. , Kozak S.L. , Michelson T.W. , Mills W.N. 1971 Coord. Chem. Rev. 6 407 -    DOI : 10.1016/S0010-8545(00)80015-6
Addison C.C. , Legan N. 1971 Quart. Chem. Rev. 25 289 -    DOI : 10.1039/qr9712500289
Lever A.B.P. , Mantiovane E. , Ramaswamy B.S. 1971 Canad. J. Chem. 49 1957 -    DOI : 10.1139/v71-315
Ahuja I.S. , Yadava C.L. , Tripathi S. 1989 Asian J. Chem. 1 195 -
Thomas J. , Parameshwaram G. 2002 Asian J. Chem. 14 1354 - 1370
Lever A.B.P. 1968 J. Chem. Edu. 45 711 -    DOI : 10.1021/ed045p711
Reedijk J. , Driesen W.L. , Groenveld W.L. 1968 Recl. Trav. Chim. 88 1095 -    DOI : 10.1002/recl.19690880912