Bis-hydrazine complexes of metal glyoxylates and mixed metal glyoxylates of 3d-metal ions of the formula M(OOCCHO)(2)(N2H4)(2), where M = Mg, Mn, Co, Ni, Cu, Zn or Cd and M1/3Co2/3(OOCCHO)(2)(N2H4)(2), where M = Mg, Mn, Ni, Zn or Cd, respectively, have been prepared and studied. The compositions of the complexes have been determined by chemical analyses. The magnetic moments and electronic spectra suggest a high-spin octahedral geometry for the metal complexes. Infrared spectral data indicate the bidentate bridging by hydrazine molecules and monodentate coordination by glyoxylate ions in both the metal and mixed metal compounds. Thermogravimetry and differential thermal analyses in air have been used to study the thermal behaviour of the complexes. The simultaneous TG-DTA traces of all the complexes show multi-step degradation and the final products are found to be the respective metal oxides in the case of metal complexes and metal cobaltites in the case of mixed metal complexes. The final residues were identified by their X-ray powder diffraction patterns. X-ray powder diffraction patterns of the complexes including mixed metal complexes are almost superimposable with in each of the series indicating isomorphism. The metal cobaltites MCo2O4, where M = Mg, Mn, Ni, Zn or Cd were also prepared by decomposing the respective mixed metal complex in a pre-heated silica crucible at about 300 degrees C, and their identities were confirmed by chemical analyses, infrared spectra and X-ray powder diffraction. (C) 2006 Elsevier B.V. All rights reserved.