Synthesis, thermal studies and spectral characterization of Co(II), Ni(II), Cu(II), and Zn(II) complexes with some polymeric diacetyl acyldihydrazone ligands

Two polymeric ligands, diacetyl oxaloyldihydrazone (DODH), diacetyl malonoylhydrazone (DMDH) and their Co(II), Ni(II), Cu(II) and Zn(II) complexes were synthesized and characterized by elemental analyses, IR, mass, H-1 & C-13 NMR, ESR and electronic spectral studies. The ligands and their complexes are highly insoluble in water and common organic solvents and decompose at high temperature. The metal atoms are embedded between two polymeric chains of the organic ligands and the monomeric unit of the polymeric chain behaves as a neutral bidentate ligand and coordinate through two > C=N groups to different metals as indicated by H-1 & C-13 NMR and IR spectral studies. The molecular weights determined by H-1 NMR and mass spectral studies suggest oligomeric nature of the ligands and their Zn(II) complexes. The magnetic susceptibility measurements and electronic spectral studies indicate a square planar geometry around the metal ion in Co(II) and Ni(II) complexes. Electronic and ESR spectral studies for Cu(II) complexes suggest a distorted octahedral stereochemistry around the metal atom and B-2(1g) as the ground state. Thermal studies (TGA and DTA) of some of the complexes in inert atmosphere show a multi-step exothermic decomposition of the bonded organic ligand at high temperature and metal (II) chloride as the end product.