Complexes of 5-(phenylazo)-2-thiohydantoin (L-1) and 5-(2-hydroxyphenylazo)-2-tliiohydantoin (HL2) with Co(II), Ni(II) and Cu(II) salts have been synthesised and characterized by elemental analysis, conductivity, magnetic susceptibility, UV-Vis, IR, ESR and TG studies. The magnetic and spectral data suggested octahedral geometry for [(LM)-M-1(OAc)(2)(H2O)(2)]-xH(2)O {M = Ni-II and Cu-II} and [(LCuCl2)-Cu-1(H2O)(H2O)-H-. (dimeric form for the latter), trigonal bipyramidal geometry for [(LCo)-Co-2(OAc)((HO)-O-2)](.)2H(2)O, square pyramidal geometry for [(LNi)-Ni-2(OAc)(H2O)](.) H2O and square planar geometry for [(LCuCl)-Cu-2](.)2H(2)O(.)TG studies confirmed the chemical formulations of these complexes and showed that their thermal degradation takes place in three to five steps, depending on the type of the ligand and the geometry of the complex. The kinetic parameters (n, E-#, A, DeltaH(#), DeltaS(#) and DeltaG(#)) of the thermal decomposition stages were computed using the Coats-Redfern and other standard equations and are discussed. (C) 2003 Elsevier B.V. All rights reserved.