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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)X2 ] 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 μs = 3.87 BM, where μs is magnetic moment due to spin-only motion, may be attributed to T1g ground state of 4F 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 T1g(F)→ T2g(F), T1g(F)→ A2g(F) and T1g(F)→T1g(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 ms value of 2.818 BM, corresponding to two unpaired electrons under octahedral symmetry. The appearance of three bands in their electronic spectra due to A2g → T2g, A2g → T1g(F) and A2g → T1g(P) spin-allowed transitions is indicative of octahedral symmetry around Ni(II). Their ν2 /ν1 values also support octahedral geometry Characterisation of Metal Complexes 2 around metal ions and decrease in Racah parameters B from free metal ions to complexes is indicative of appreciable covalent character in M-L bonds.

Spectroscopic Characterisation of Metal Complexes with Tetradentate Ligand