New organometallic single-source precursors for CuGaS2 – polytypism in gallite nanocrystals obtained by thermolysis

Abstract

The complex [(ⁱPr₃PCu)₂(Me₂Ga)₂(SCH₂CH₂S)₂] (4) was synthesized from trimethylgallium, [(ⁱPr₃PCu)₄(SCH₂CH₂S)₂] (1) and ethanedithiol by elimination of methane. The related monomethyl compound [(ⁱPr₃PCu)₂(MeGaSPh)₂(SCH₂CH₂S)₂] (5) has been prepared from [(ⁱPr₃PCuSPh)₃] (2) and [(MeGaSCH₂CH₂S)₂] (3) by a ligand exchange reaction in tetrahydrofuran solution. The molecular structures of 1 and 3–5 were determined by single crystal X-ray diffraction. Thermolysis of 4 and 5 results in the formation of the ternary semiconductor CuGaS₂, gallite. The residue of 5 was characterized using X-ray powder diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy. The CuGaS₂ crystals obtained are mainly hexagonal plates of around 200 to 300 nm diameter and 10 to 30 nm thickness, exhibiting an unusual metastable hexagonal crystal structure, related to wurtzite. Partially, the usual tetragonal chalcopyrite structure or its disordered cubic zinc-blende analogue is realized by stacking faults, resulting in an overall similarity to the zinc-blende–wurtzite polytypism in ZnS and related compounds.