Gas-phase formation of zinc/cadmium chalcogenide cluster complexes and their solid-state thermal decomposition to form II-VI nanoparticulate material

Abstract

Gas-phase reactions between R ₂ Zn (R=Me and Et) and ^t BuSH produce cluster complexes of the type [RZnS ^t Bu] _n . These clusters, along with [MeZnS ^t Bu(py)] ₂ (py=pyridine), have been characterised by ¹³ C{ ¹ H} solid-state NMR. On heating to 100°C in the solid-state, the complexes [MeZnS ^t Bu] ₅ and [MeZnS ^t Bu(py)] ₂ release dimethylzinc (Me ₂ Zn) to form the zinc bis(thiolate) compound, [Zn(S ^t Bu) ₂ ] _n , with further heating (>200°C) leading to the formation of ZnS. The ethyl analogue, [EtZnS ^t Bu] ₅ , does not lose Et ₂ Zn on heating and thermogravimetric analysis (TGA) suggests a different decomposition pathway, one which mainly involves loss of the organic moieties without the concurrent loss of volatile Zn or S compounds, although ZnS is again the final thermal decomposition product. The decomposition of the involatile pentamers, [MeZnS ^t Bu] ₅ and [EtZnS ^t Bu] ₅ , and the dimer, [MeZnS ^t Bu(py)] ₂ , proceeds at higher temperature (200-350°C) to give agglomerates of ME nanoparticulate material, with the individual particles having diameters of 2-20 nm in all cases. The mechanistic pathway by which these clusters decompose appears to be highly dependent upon the R group (Me or Et) present within the cluster. Preliminary results suggest that complexes of the type [RME ^t Bu] _n are also produced from the gas-phase reactions of Me ₂ Zn with ^t BuSeH and from Me ₂ Cd with ^t BuSH.