MAGNETIC AND ELECTRONIC SPECTRAL STUDIES OF FOUR, FIVE AND SIX COORDINATED COMPLEXES OF SUBSTITUTED HYDRAZIDE AND HYDRAZONES WITH DIVALENT NICKEL AND COBALT METAL IONS

mole) followed by adding an ethanolic solution of nickel (II) chloride (50 ml; 0.005 mole) dropwise with constant shaking. The reaction mixture (pH ~ 2.2.-2.7) was refluxed for about 3 hrs., concentrated and kept overnight. Light bluish or greenish crystals were obtained. These crystals after filteration were washed with acetone, recrystallised from ethanol and dried under vacuum. Yield ~ 50-55%. The solution spectra of [Co(AIH)] 2 is quite different from the spectra of other compounds described herein. The broad high intensity bands are observed ~5850 and ~15800 cm -1 and are multistructured, perhaps due to the mixing in of metal d-orbitals with ligand functions. The spectral bands are consistent with the tetrahedral environmental around the metal atom and may be assigned to, 4 A 2  4 T 1g (F) and 4 A 2  4 T 1g (P), respectively.

Metal complexes of divalent Nickel and Cobalt metal ions have been synthesized with picolinic acid hydrazide (PH) , ortho -hydroxy acetophenone picolinoyl hydrazone ( APH) and ortho-hydroxy acetophenone iso-nicotinoyl hydrazone (AIH) ligands and were isolated at both high pH and low pH. These complexes were characterized by elemental analyses and also by electronic spectral studies and magnetic measurements. Ligands PH and AIH act as tridentate, while APH is tetradentate. All form two types of complexes, depending upon pH of the reaction mixture. At high pH complexes formed are monomeric while at high pH complexes were found to be dimeric. Dimerisation is initiated by enolic oxygen which acts like a bridging ligand between two metal ions.

…………………………………………………………………………………………………….... Introduction:-
Metal-ligand interactions involving a large pH range and non-aqueous solvents present many interesting points requiring further elucidation. In the former case, it has been claimed that the reaction product undergoes dimerisation depending upon the pH of the medium. Attempts have been made in the present paper to investigate this aspect on the basis of magnetic and spectral data. Researchers have paid attention to hydrazones and their complexes with metal ions because they act as very important stereochemical models in the field of coordination chemistry on account of ease of their preparation and versatility in strucure .It has been established that the carbonyl linkage i.e C=O in hydrazides is accountable for the biological activities such as anti bacterial ,antifungal ,antitumor and herbicidal (1,2).More recently development of new drug metal complexes have gained attention and special interest in the area of coordination chemistry (3,4) .Complexes of transition metals of substituted hydrazones play remarkable role in a number of catalytic reaction like polymerisation, asymmetric cyclopropanation and oxidation (5)(6)(7).Structural characterisation of some of the complexes of hydrazides have revealed some interesting information about them like their efficacy and tendency to serve as planar pentadentate ligands in its complexes (8)(9)(10)(11) along with its tridentate character (12) .These ligands not only show keto-enol tautomerism but also can coordinate in monoanionic (13) , dianionic (14) , neutral (14) or tetraanionic (15) forms with the metal ions having either the coordination number six or seven (14) producing mononuclear as well as binuclear species. However it is also an established fact that it all is dependent on the reaction conditions like metal ion , its concentration , nature of hydrazide and pH of the medium (16). Coordination chemistry of some substituted aroyl hydrazones has revealed combining of donor postions like as protonated amide or deprotonated amide oxygen, an imine nitrogen 322 (> C N-) of hydrazone (R 2 C=N-NR 2 ' ) moiety as well as some additional donor positions (generally Nitogen or Oxygen) presented given by aldehyde or ketone to form the Schiff base (17).
The magnetic measurements are of immense importance in determining the nature of bond and stereochemistry of the complexes. The interpretations revealed by the studies of the electronic spectra and magnetic properties of many complexes formed by the metal ions of 3-d transition series and the consequential implementation of ligand-field theory were a major element in the renaissance of transition metal chemistry in the 1960s (18).
The complexes of divalent nickel and cobalt are most extensively studied, because their structures exemplify some important fundamental orbital and electronic principles relevant to the critical study of coordination compounds. The most interesting feature of these metal ions is the exhibition of varied stereochemistries, viz., square planar (19), tetrahedral (20), square pyramidal (21), tetragonal (22) or pentagonal bipyramidal (23).
The pyridine based acid hydrazides and their corresponding hydrazones with o-hydroxyacetophenone, provide suitable coordination sites in the form of phenolic and ketonic oxygen. These compounds may act differently depending upon pH of the reaction mixture. Thus, the ligands chosen for the present studies exhibit keto enolic tautomeric forms. These compounds, therefore, are best suited for carrying out basic studies on bridged complexes.
The present studies have, therefore, been initiated in the direction of evaluating the bonding, structure, geometry and other characteristics of metal chelates. The present ligands have potential donor sites, viz., pyridine nitrogen, ketonic or enolic amide oxygen, hydrazinic or phenolic oxygen and azomethine nitrogen , which are suitably placed for coordination. The interesting feature is the presence of two oxygen atoms and either of them may act as a bridging atom in between the two atoms of metal.

Physical Measurements Magnetic Measurements
The measurements of magnetic susceptibility of powdered complexes, at room temperature were carried out by Guoy's balance. Mercury(II) tetrathiocyanatocobaltate(II) [HgCo(CNS) 4 ] ( g =16.442x10 -6 CGS units at 293A) was used as a calibrant. Tube constant was calculated from time to time to check the satisfactory working of the apparatus.

Electronic Spectral Measurements
The electronic spectra of the complexes at room temperature were recorded in ethanol, dimethylformamide or nujol mull on a Cary-14 automatic recording spectrophotometer. These measurements were carried out at Indian Institute of Technology, Kanpur.

(iii) pH Measurements
The pH of the solutions was measured at room temperature by Elico (LI-10) pH meter, using combined electrodes. (iv) Molecular Weight Measurements measurement of molecular weight was made by Beckmann's cryoscopic method (v) Chemical Analyses The metal contents in all the complexes were estimated as under: A known quantity of the complex was heated with a very small amount of concentrated sulphuric acid and then repeatedly with concentrated nitric acid until all the organic matter was decomposed. The residue was then dissolved in doubly distilled water or sometimes dilute hydrochloric acid was added to it and made upto a known volume, from which the metals were estimated by standard literature methods (24) .
The microanalyses of carbon(C), hydrogen (H) and nitrogen (N) for all the compounds were carried out by the Microanalytical Division, CDRI, Lucknow.

Methods Of Calculations Magnetic Susceptibility
Magnetic susceptibility ( g ) of complexes has been calculated from the formula, For applying the diamagnetic corrections, using Pascal's constants (25), it is convenient to deal with in terms of susceptibility per mole ( m ) of the compound, using the formula, The effective magnetic moment is then calculated with the help of the following formula.
Where T = temperature in absolute units.

Ligand field Parameters
The calculation of various ligand field parameters viz., Ds, Dt, Dq xy , D q z and parameters of Normalised Spherical Harmonic (NSH) Hamiltonian Theory (26) , viz., DS, DT, DQ, DQ L and DQ Z have been made .

SYNTHESIS OF PICOLINIC ACID HYDRAZIDE (PH)
It was synthesised by refluxing ethyl-2-picolinate and hydrazine hydrate (99%) in 1:1 molar ratio on a water bath for five hours. On cooling, white crystalline product was obtained. It was filtered and recrystallised from ethanol when colourless needle shaped crystals (m.pt. 101) were obtained. Yield  85%. Calcd. for C 6

Methods of preparation and isolation of complexes
Two types of nickel (II) and cobalt (II) complexes with PH , APH and AIH were synthesised at low and high pH as follows:

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The analytical data of the complexes reveal their formulae to be Ni (C 6 H 7 N 3 O) 2 Cl 2 , Ni(C 14 H 12 N 3 O 2 )Cl and Ni(C 14 H 12 N 3 0 2 ) 2 , respectively and their results are given in Table (A). The complexes do not undergo decomposition on keeping in air and are stable upto 275. They are soluble in water, ethanol and dimethylformamide.

High pH Complexes
To a warm ethanolic solution of nickel (II) chloride (50 ml; 0.01 mole) and PH (50 ml; 0.02 mole), an ethanolic solution of potassium hydroxide was added dropwise with constant stirring, till pH became ~ 4.9. Then the refluxing of the reaction mixture was done for 1 hr, when a green precipitate was obtained. It was cooled, filtered, washed with ethanol and ether and finally dried under vacuum. Yield ~ 70%.
The ethanolic solution of PH (50 ml; 0.02 mole) was refluxed with o-hydroxyacetophenone (25 ml; 0.021 mole) for 1 hr. To the hot solution, warm ethanolic solution of nickel (II) chloride (100 ml; 0.01 mole) was added gradually. The pH was then raised to ~ 5.0 by dropwise addition of ethanolic solution of potassium hydroxide, when the blue solution changed to olive green. On refluxing it for 1 hr., a precipitate was obtained. It was then filtered then washed with ethanol and ether and finally dried under vacuum. Yield ~ 50%.
Ethanolic mixture of INH (150 ml; 0.04 mole) and o-hydroxyacetophenone ( 25 ml; 0.042 mole) was refluxed for 1 hr. To this, was added a hot ethanolic solution of nickel (II) chloride (100 ml; 0.02 mole). The resulting brown solution did not show any perceptible precipitation even after raising the pH to 5.2. The solution was then kept in a refrigerator for 48 hrs, whereby orange-red crystals got separated from the oily liquid, which were separated by filtration, washed with ethanol, ether and dried in an oven at 110. Yield ~ 35%.
The analytical data of the complexes reveal their formulae to be Ni(C 6 H 6 N 3 O)Cl, Ni(C 14 H 11 N 3 O 2 ) and Ni(C 14 H 11 N 3 O 2 ), respectively and the results are given in Table (A). The complexes formed with PH and APH ligands are insoluble in water, ethanol, partially soluble in methanol and soluble in diemethylformamide, whilst the AIH complex is soluble in dimethylformamide only. The analyses of the complexes conform to the formulae Co(C 6 H 7 N 3 O) 2 Cl 2 , Co(C 14 H 12 N 3 O 2 )Cl and Co(C 14 H 12 N 3 0 2 ) 2 , respectively and the data are given in Table (B). The complexes are stable upto 300. They are soluble in water and ethanol, but are insoluble in other organic solvents.

High pH complexes
To a solution of cobalt (II) chloride (100ml; 0.01 mole) and PH(100ml; 0.033 mole) in ethanol, an ethanolic solution of potassium hydroxide was added dropwise till its pH become~4.5. The reaction mixture was refluxed for an hour. The precipitate so obtained was filtered after cooling, washed with ethanol, ether and dried under vacuum. Yield~60%.
325 INH (0.025 mole) and o-hydroxyacetophenone (0.028 mole) were mixed in 100 ml. ethanol and refluxed for an hour. A brown solution was obtained on adding a warm solution of cobalt (II) chloride in ethanol (100 ml; 0.02 mole). On adding ethanolic potassium hydroxide solution, the solution developed a dark blue colour at pH~5.1. It was concentrated and kept overnight. Fine bluish red crystals were obtained. These crystals were then filtered and washed successively with ethanol, ether and dried under vacuum. Yield ~ 45%.
The analyses of the complexes conform to the formulae Co(C 6 H 6 N 3 O)Cl and Co(C 14 H 11 N 3 O 2 ) respectively and the results are given in Table (B). The complexes are stable upto 290. They are insoluble in water and ethanol, but soluble in dimethylformamide.
The bromo complexes of nickel (II) and cobalt (II) with PH and APH (at low pH) were prepared by the method of Denk and Madan (27). Their corresponding nitrato complexes were synthesised by taking the nitrate salts of the metals. Preparation of thiocyanato complexes were made by adding potassium thiocyanate to the metal chloride solution. The preparations of bromo, nitrato and thiocyanato complexes were also attempted for all the three ligands, but with APH (at high pH) and AIH (at low as well as high pH) similar products were obtained (as confirmed by analytical and i.r. spectral measurements).

MAGNETIC AND ELECTRONIC SPECTRAL STUDIES NICKEL (II) COMPLEXES
The magnetic data for nickel (II) complexes at room temperature are reported in Table ( complexes and may be probably related to the presence of low symmetry components in these complexes. The magnetic moments of nickel (II) complexes of PH and APH synthesised at high pH are much lower than the corresponding compounds at low pH. It appears that the substandard magnetic moments (2.40-2.60 B.M.) for these compounds may be due to metal-metal exchange coupling through enolic oxygen bridging ( vide i.r.) .
The AIH complex synthesised at high pH shows a magnetic moment 0.45 B.M., a value in the range often observed for spin paired ions and suggests square planar environment around the metal atom.
The spectra of the solution of [Ni(PH) 2 ]X 2 and [Ni(AIH) 2 ] are similar and show two bands that are identically positioned ~ 11350-11800 and 16250-16950 cm -1 with a shoulder ~ 9700-10500 cm -1 . This presence of the shoulder must have been there due to of the splitting of the first band into two components, which indicates that tetragonal distortion is there in case of such complexes. The band at ~ 28500 cm -1 emerges as a broad band. The spectra of these complexes can best be interpreted by assuming the effective symmetry to be D 4h . Thus, the various bands can be assigned to: . It is found that the bands formed in these complexes do not follow any regular pattern, so it may be concluded that they are anion independent.
The complexes [Ni(AIH)] 2 , however, appears to be quite distinct from other complexes in being orange-red in colour and diamagnetic in nature. Its solution spectra exhibits two bands ~15500 and 19000 cm -1 with a weak shoulder at 14200 cm -1 . The former band characteristic of square planar geometry, may be assigned to first spin allowed transition, 1 A 1g  1 B 1g . The bands at 19000 and 14200 cm -1 may be due to 1 A 1g  1 A 2g and spin-forbidden 1 A 1g  3 B 1g transitionsrespectively. The energies of these bands are comparable to d-d bands observed for other square planar Schiff's base complexes.
The intense higher energy bands ~ 34600 cm -1 observed in the spectra of all complexes except those of [Ni(PH 2 )]X 2 and [Ni(PH)X] 2 may be due to ligand -* transition of the phenolic group. The solution spectra of [Co(PH) 2 ]X 2 and [Co(AIH) 2 ] show two bands discernable at ~8200, 8650 cm -1 and ~15800, 16200 cm -1 , respectively with a broad band envelope ~20000 cm -1 having two bands ~18000 and 22000 cm -1 . The spectra are consistent with the octahedral environment around the metal atom. However, the chances of an idealised symmetry are remote due to the presence of donor atoms of unequal strength and size. The various bands can be assigned to: 4 T 1g (F)  4 T 2g (F); 4 T 1g (F)  4 A 2g (F) and 4 T 1g (F)  4 T 1g (P), respectively in order of increasing energy. Distortion of the molecule gives rise to multiple bands and this is consistent with the lower symmetry elements present in these compounds. The amount of distortion cannot be calculated since the splitting of bands is not observed in the spectra of complexes.

COBALT (II) COMPLEXES
The absorption maxima of the ligand field bands in the spectra of [Co(APH)X], [Co(PH)X] 2 and [Co(APH)] 2 are nearly identical and show three bands in 9200-10450, 16800-17500, 22200-23250 cm -1 regions which resembles the spectra of five-coordinate complexes , structures of which have been authenticated by X-ray measurements. These complexes are isomorphous with the corresponding nickel (II) complexes. This also points towards the pentacoordination around the cobalt ion. The tri-and tetradentate nature of PH and APH, presence of one anion the coordination sphere, dimeric nature of [Co(PH)X] 2 and [Co(APH)] 2 , conclusively point towards their square pyramidal geometry. Thus by assuming that the effectual symmetry to be C 4 , the various bands may be assigned to : 4 A 2 (F)  4 B 1 (9200-10650 cm -1 ); 4 A 2 (F)  4 E (16800-17500 cm -1 ) and 4 A 2 (F)  4 A 2 (P) (22200-23250 cm -1 ) . This symmetry is, however, lower than C 4 , since the donor set, e.g. N 2 O 2 X or N 2 O 3 cannot conform to idealised symmetry. Applying the statement that the tensor Hamiltonian for C 4 group is identical with that for D 4h the description of D 4h applies well in the square pyramidal complexes conforming of C 4 symmetries . Various parameters used to define the distortion viz., Dt, Dq xy , and Dq z are calculated and included in Table (E) and (F).

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The solution spectra of [Co(AIH)] 2 is quite different from the spectra of other compounds described herein. The broad high intensity bands are observed ~5850 and ~15800 cm -1 and are multistructured, perhaps due to the mixing in of metal d-orbitals with ligand functions. The spectral bands are consistent with the tetrahedral environmental around the metal atom and may be assigned to, 4 A 2  4 T 1g (F) and 4 A 2  4 T 1g (P), respectively.  Conclusion:-Following conclusions are drawn on the basis of above studies: (a)Ligands PH and AIH act as tridentate, while APH is tetradentate. All form two types of complexes, depending upon pH of the reaction mixture.
(b)Complexes synthesised at low and high pH are monomeric and dimeric, respectively. (c) In complexes synthesised at high pH, the dimerisation is initiated by enolic oxygen, which acts as a bridge between the two metal atoms.
(d)In PH and APH complexes, besides phenolic oxygen, ketonic or enolic oxygen and hydrazinic or azomethine nitrogen, pyridine nitrogen also takes part in coordination, while it is not so in AIH complexes.