Research and Control Laboratory, Rourkela Steel Plant, Rourkela-769 011 Department of Chemistry, Regional Engineering College, Rourkela-769 008 Manuscript received 7 February 1983, revised 10 November 1983, accepted 25 March 1984 Several mixed ligand complexes of copper(II) and nickel(Il) having the compositions [M(aa)(tca)] and [M(aa)(tca)L2], where aaH is acetylacetone, tcaH H is tricloroacetlc acid ; L is \(\gamma\)·picoline, imidazole, 2-picoline· N-oxide or thiourea and M is Cu(II) or Ni(II), have been isolated and characterised on the basis of their analyses, molar conductance magnetic susceptibility, infrared, electronic spectral data and thermogravimetric measurements. The infrared spectra reveal the presence of uninegative bidentate acetyl acetonate and trichloroacetate groups in all these complexes. As the temperature increases, the mixed ligand complexes start decomposing with the loss of neutral donor ligand, followed by trichloroacetate ion and acetylacetonate ion in definite steps and ultimately forming MO at 600-675°. Square planar, tetrahedral. distorted octahedral and octahedral structures have been proposed for the complexes, [Cu(aa)(tca)], [Ni(aa)(tca)], [Cu(aa)-{tca)L2] and [Ni(aa)(tca)L2], respectively.