Synthesis and spectroscopic properties of cobalt(III) complexes of some aroyl hydrazones: X-ray crystal structures of one cobalt(III) complex and two aroyl hydrazone ligands

Cobalt(III) complexes of diacetyl monooxime benzoyl hydrazone (dmoBH2) and diacetyl monooxime isonicotinoyl hydrazone (dmoInH2) have been synthesized and characterized by elemental analyses and spectroscopic methods. The X-ray crystal structures of the two hydrazone ligands, as well as that of the cobalt(III) complex [CoIII(dmoInH)2]Cl·2H2O, are also reported. It is found that in the cobalt(III) complexes the Co(III) ion is hexa-coordinated, the hydrazone ligands behaving as mono-anionic tridentate O,N,N donors. In the [CoIII(dmoInH)2]Cl·2H2O complex, the amide and the oxime hydrogens are deprotonated for both the ligands, while the isonicotine nitrogens are protonated. In the [CoIII(dmoBH)2]Cl complex, only the amide nitrogens are deprotonated. It is shown that the additional hydrogen bonding capability of the isonicotine nitrogen results in different conformation and supramolecular structure for dmoInH2, compared to dmoBH2, in the solid state. Comparing the structure of the [CoIII(dmoInH)2]Cl·2H2O with that of the Zn(II) complex of the same ligand, reported earlier, it is seen that the metal ion has a profound influence on the supramolecular structure, due to change in geometrical dispositions of the chelate rings.