The synthesis and characterization of a series of homologous tetranuclear complexes [((i)Pr3PCu)2(MR2)2(SCH2CH2S)2] (MR2 = GaMe2 (2), GaEt2 (3), Ga(i)Pr2 (4), Ga(n)Bu2 (5) and InMe2 (6), InEt2 (7), In(i)Pr2 (8), In(n)Bu2 (9)) and of related compounds [((i)Pr3PCu)3(MR2)(SCH2CH2S)2] (MR2 = GaMe2 (10), GaEt2 (11), Ga(i)Pr2 (12), Ga(n)Bu2 (13) and InMe2 (14), InEt2 (15), In(i)Pr2 (16), In(n)Bu2 (17)) are presented. The molecular structures of these were determined by single crystal X-ray diffraction. Thermolysis processes of all the representatives of 2-9 were investigated by simultaneous thermal analysis and thermal decomposition in a nitrogen atmosphere in a quartz glass tube. According to powder X-ray diffraction studies these thermolysis residues predominantly consist of CuMS2 (M = Ga, In), which mainly occurred in the well known tetragonal chalcopyrite-type structure and partially in the hexagonal wurtzite-type structure. As expected from their composition, representatives of 10-17 form mixtures of CuMS2 and large amounts of Cu(2-x)S upon thermolysis.