COPPER(II) COMPLEXES OF NOVEL TRIPODAL LIGANDS CONTAINING PHENOLATE AND BENZIMIDAZOLE PYRIDINE PENDANTS - SYNTHESIS, STRUCTURE, SPECTRA ANDELECTROCHEMICAL-BEHAVIOR

Mononuclear copper(II) complexes of tri- and tetra-dentate tripodal li gands containing phenolic hydroxyl and benzimidazole or pyridine group s have been isolated. They are of the type (CuL(X)].nH2O, [CuL(H2O)]X. nH2O or [CuL].nH2O where X = Cl-, ClO4-, N3- or NCS- and n = 0-4. The electronic spectra of all the complexes exhibit a broad absorption ban d around 14000 cm-1 and the polycrystalline as well as the frozen-solu tion EPR spectra are axial, indicating square-based geometries. The cr ystal structure of [CuL(Cl)] [HL = -hydroxy-5-nitrobenzyl)bis(2-pyridy l-methyl)amine] revealed a square-pyramidal geometry around Cu(II). Th e mononuclear complex crystallises in the triclinic space group P1BAR with a = 6.938(1), b = 11.782(6), c = 12.678(3) angstrom and alpha = 1 14.56(3), beta = 92.70(2), gamma = 95.36(2)-degrees. The co-ordination plane is comprised of one tertiary amine and two pyridine nitrogens a nd a chloride ion. The phenolate ion unusually occupies the axial site , possibly due to the electron-withdrawing p-nitro group. The enhanced pi delocalisation involving the p-nitrophenolate donor elevates the E 1/2 values. The spectral and electrochemical results suggest the order of donor strength as nitrophenolate < pyridine < benzimidazole in the tridentate and nitrophenolate < benzimidazole < pyridine in the tetra dentate ligand complexes.