Structure and evolved gas analyses (TG/DTA-MS and TG-FTIR) of mer-trichlorotris(thiourea)-indium(III), a precursor for indium sulfide thin films

Abstract

The indium complex, mer-trichlorotris(thiourea)-indium(III) (In(tu)3Cl3, 1), crystallized from aqueous solution of InCl3 and SC(NH2)2 (tu) with molar ratio of 1:3, is a single-source precursor for In2S3 films by chemical spray pyrolysis. The structural model of the triclinic crystal 1 (space group P-1 with a = 8.4842(2) A, b = 10.5174(2) A, c = 13.1767(2) A, α = 111.1870(10)°, β = 98.0870(10)°, γ = 97.889(2)°) has been improved by single crystal X-ray diffraction analysis through successful separation of the disordered positions of the asymmetric complex molecule situated on the inversion centre into two spatial arrangements. Thermal decomposition of 1 occurs with very similar mass loss courses till 400 °C in both nitrogen and air, anyhow the DTA curve indicates a gas-phase oxidation with an additional exothermic heat effect at 255 °C in air. Partial or more advanced oxidation of the initially evolved CS2 has taken place in both atmospheres, as its oxidation products, SO2, COS, CO2 are accompanied by the release of NH3, HCl in temperature range of 205–275 °C, while H2NCN and HCN evolve in air. In the third mass loss step, in the temperature interval of 405–750 °C in nitrogen and 405–700 °C in air, two processes, evaporation and oxidation of the solid residues are competing with each other, resulting in final decomposition product of 1 in air In2O3, while also some In2O3 in inert atmosphere beyond the main phase of In2S3 where, in addition considerable extent of loss of indium occurs, probably through volatile dimeric indium chloride species, which could not be detected either by EGA-MS or EGA-FTIR systems of ours. Nevertheless, evolution of HNCS is confirmed by EGA-FTIR, and release of CO2, H2NCN, SO2, and a little HCl is detected at temperatures above 450 °C in both atmospheres.