Facile one-pot template synthesis of isotypic Co(II), Ni(II) and Cu(II) complexes of a Schiff base derived from glyoxylic acid and ethyl carbazate: Spectroscopic, structural and thermal studies

Glyoxylic acid and ethyl carbazate condense in situ in the reaction medium and react with metal nitrates of Co, Ni or Cu to yield isostructural metal complexes with the general formula [M(gly-ec)₂(H₂O)₂] (M = Co²⁺ (1), Ni²⁺ (2) and Cu²⁺ (3); Hgly-ec = ethoxycarbonyl-hydrazono-acetic acid). These products are elucidated through various physicochemical techniques including powder and single-crystal X-ray diffraction. X-ray crystallography of complexes 1 and 3 reveals that two anionic Schiff base ligands are coordinated to the metal ion via (N, O) bidentate chelation and situated trans to each other in equatorial positions and are nearly coplanar with the metal atom. The two coordinated water molecules occupy the trans axial positions, with a slightly distorted octahedral geometry. The thermal behavior of complexes 1–3 is studied in air and nitrogen atmosphere from 30 to 800 °C. In both mediums, all of the complexes show endothermic followed by exothermic decomposition to yield metal oxides as the end products at low temperature. Hence, these isotypic complexes may be used as solid-state precursors for the preparation of respective metal oxides due to their low temperatures of decomposition.