Transition metal complexes of pyrazinecarboxylic acids with neutral hydrazine as a ligand: Synthesis, spectroscopic, thermal and XRD studies

New divalent Co, Ni, Zn and Cd pyrazinecarboxylate hydrazinates of the formulae M(pyzCOO)₂·nN₂H₄·xH ₂O and Mpyz(COO)₂·N₂H ₄·xH₂O obtained by the reaction of respective metal nitrate hydrates with 2-pyrazinecarboxylic (HpyzCOO)/2,3-pyrazinedicarboxylic (H₂pyz(COO)₂) acid and hydrazine hydrate have been characterized on the basis of analytical, spectroscopic (electronic and infrared), thermal and X-ray powder diffraction studies. The electronic spectroscopic data suggest that the cobalt and nickel complexes are of spin-free (high-spin) type with octahedral geometry. The IR absorption bands of N-N stretching in the range 980-972 cm^-1 unambiguously prove the bidentate bridging nature of the N₂H₄ ligand. The hydrazinate complexes of 2,3-pyrazinedicarboxylate lose hydrazine molecule exothermally, whereas 2-pyrazinecarboxylate compounds lose the same endothermally. Further, all the complexes undergo endothermic (dehydration and/or dehydrazination) followed by exothermic decomposition except the Zn and Cd complexes of 2,3-pyrazinedicarboxylate, which show only exothermic decomposition. In order to know the isomorphic nature among the complexes, the X-ray powder patterns have been compared.