Mixed ligand complexes of Co(II), Ni(II), Cu(II) and Cd(II)} with 4-(2-pyridylmethylenamino)-3-mercapto-5-benzayl-1,2,4-triazole (L1), 4-(3-pyridylmethylenamino)-3-mercapto-5-benzayl-1,2,4-triazole (L2), 4-(4-pyridylmethylenamino)-3-mercapto-5-benzayl-1,2,4-triazole (L3),bipyridyl (bipy) and 1,10-phenanthroline (phen) were prepared. They have general formula [M(L)(bipy)Cl2].nH2O and [M(L)(phen)Cl2].nH2O, where M=Co(II); Ni(II); Cu(II) or Cd(II). The complexes have been characterized by elemental analysis, spectroscopic measurements (FT-IR, UV-Vis.),transmission electron microscopy (TEM), as well as molar conductance, magnetic measurements and thermal studies. The complexes are hexacoordinated and the structure, thus assumed to have an octahedral geometry. The prepared materials show the existence of nano-particles with spherical shape. The TEM image shows that the particle diameter is 35.2 - 32.8 nm with a mean particle size of 34 nm. The thermal decomposition study of the prepared complexes was monitored by TG, DTG and DTA analysis in a dynamic nitrogen atmosphere. TG, DTG and DTA studies confirmed the chemical formulations of these complexes. The relative thermal stability of the chelates is evaluated. The final decomposition products were found to be the corresponding metal sulfides. The thermodynamic activation parameters such as ΔS#, ΔH# and ΔG# were calculated from the TG curves.