Structure and thermal behaviour of dichlorobis(thiourea)cadmium(II), a single-source precursor for CdS thin films

The title compound (1) crystallites in the space group Pmn2(1) with a = 13.110 (3), b = 5.813(1) and c = 6.482(1) Angstrom. Its crystal structure was redetermined from three-dimensional single-crystal data to a final R-value of 0.0221. The Cd2+ ion is tetrahedrally coordinated to two sulfur atoms from the tiourea ligand (Cd-S = 2.509 Angstrom) and to two chloride ions at distances 2.545 and 2.518 Angstrom. When heated in air or in an inert atmosphere 1 undergoes a complex degradation process which was studied in situ by simultaneous TG/DTA as well as by EGA-FTIR. The gaseous species evolved include NH3, HCl, H2NCN, HNCS and CS2, which upon oxidation yield also HCN, SO2, COS and CO2. In the solid residue, NH4CdCl3 and CdS were detected by X-ray diffraction, Elemental and XPS analyses also indicated the presence of Cl and N as well as some carbon residue. The results of the thermoanalytical study are not directly applicable to the spray pyrolysis process because of the different experimental conditions, but they nevertheless indicate that it is extremely difficult to prepare impurity-free CdS. The formation of HCN, not detected earlier, should also be taken into account when designing the process parameters and safety measures.