A Schiff's base containing tetradenticity N,N-bis-(3-hydroxyquinoxaline)-2-carboxidine-1,8-diaminenaphthalene, henceforth abbreviated as NBHCN, has been prepared by condensation of two moles of 3-hydroxyquinoxaline-2-carboxaldehyde with one mole of 1,8-diaminonaphthalene. This Schiff's base has been made to undergo complexation with Co(II) and Ni(II) metal ions. On the basis of their elemental analysis and molar conductivity values, the complexes have been formulated as [M(NBHCN)X 2 ] where X stands for water, pyridine and α-picoline which act as secondary ligands. The comparison of infrared spectra of metal complexes with that of NBHCN (Schiff's base ligand) indicates its coordination through two azomethine nitrogen and two deprotonated hydroxyl oxygen atoms. Thus, the ligand acts as a bivalent tetradentate anionic one joining through four potential sites to the metal ions. The magnetic moments of Co(II) complexes have been found in the range of 4.90-4.91 Bohr Magnetone (BM) which is greater than three unpaired electrons in spin free octahedral complexes of Co(II) metal ion. The slightly excess value of magnetic moment of Co(II) complexes from μ s = 3.87 BM, where μ s is magnetic moment due to spin-only motion, may be attributed to 4 T 1g ground state of 4 F term of d-system in octahedral symmetry, being orbitally triply degenerate, makes sufficient contribution to the magnetic moment of the complexes. The octahedral symmetry of Co(II) complexes has further been confirmed by their electronic spectra which display three bands due 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) spin-allowed transitions. The magnetic moment values of Ni(II) complexes have been found in the range of 3.0-3.2 BM which is also greater than its m s value of 2.818 BM, corresponding to two unpaired electrons under octahedral symmetry. The appearance of three bands in their electronic spectra due to 3 A 2g → 3 T 2g , 3 A 2g → 3 T 1g(F) and 3 A 2g → 3 T 1g(P) spin-allowed transitions is indicative of octahedral symmetry around Ni(II). Their ν 2 /ν 1 values also support octahedral geometry

A multidentate ligand, 1-benzoyl-2-(2′-carboxylphenyl)iminopropane (BIPH) has been prepared by the condensation of 1-phenylbutane-1,3-dione and anthranilic acid. This ligand has been used for chelation with Co(II), Ni(II) and Zn(II) metal ions as primary ligand while H2O, pyridine and α-picoline as the secondary ligands. The low value of molar conductivity of 10-3 M DMF solution of complexes shows that all the complexes are non-electrolyte. The comparison of IR spectra of complexes with that of free ligand reveals that the ligand chelates through deprotonated enolic-OH group oxygen and azomethine nitrogen and not through azomethine nitrogen and carboxylic oxygen or through carbonyl oxygen and carboxylic oxygen. On the basis of magnetic moment values and electronic spectra, octahedral symmetry has been assigned to these complexes with tetragonal distortion. Thermogravimetric analysis also confirms the tetragonal distortion with elongation along z-axis in complexes.

<em>Some complexes of Ni(II) have been prepared with 2-thio-3-acetyl hydantoin (TAHN) and 2-formyl pyridine thiosemicarbazone (FPTS). On the basis of elemental analysis and molar conductivity, the complexes have been formulated as NiL₂X₂, where L = TAHN or FPTS and X = Cl^–, Br^–, NCS^–, ClO₄^–. The infrared spectra of complexes and free ligand reveal that the ligand TAHN is co-ordinated through sulphur and acetyl oxygen, while FPTS ligand co-ordinates through heterocyclic nitrogen and sulphur to Ni(II) metal ion. The magnetic moment of these complexes are found to be 3.20-3.25 B.M. The values are greater than value (2.828 B.M) corresponding to two unpaired electrons of a d⁸-system. The appearance of four absorption bands in their electronic spectra reveal, the tetragonal distortion in the octahedral symmetry of complexes. The zero field splitting parameter(D) and the other crystal field parameters like Dq_(xy), Dq_(z), Dt have been calculated. The results show that, the tetragonal distortion parameter (Dt) increases in the order of NCS^–&lt; Cl^– &lt; Br^– while the zero field splitting parameter (D) also increases in the same order for both the planer ligands.</em>