STRUCTURE AND THERMAL-BEHAVIOR OF DICHLOROBIS(THIOUREA)CADMIUM(II), ASINGLE-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 stru cture 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 heate d in air or in an inert atmosphere 1 undergoes a complex degradation p rocess which was studied in situ by simultaneous TG/DTA as well as by EGA-FTIR. The gaseous species evolved include NH3, HCl, H2NCN, HNCS an d CS2, which upon oxidation yield also HCN, SO2, COS and CO2. In the s olid residue, NH4CdCl3 and CdS were detected by X-ray diffraction, Ele mental and XPS analyses also indicated the presence of Cl and N as wel l as some carbon residue. The results of the thermoanalytical study ar e not directly applicable to the spray pyrolysis process because of th e different experimental conditions, but they nevertheless indicate th at it is extremely difficult to prepare impurity-free CdS. The formati on of HCN, not detected earlier, should also be taken into account whe n designing the process parameters and safety measures.