Accessing γ-Ga2S3 by solventless thermolysis of gallium xanthates: a low-temperature limit for crystalline products

Alkyl-xanthato gallium(iii) complexes of the form [Ga(S2COR)(3)], where R = Me (1), Et (2), Pr-i (3), Pr-n (4), Bu-n (5), Bu-s (6) and Bu-i (7), have been synthesized and fully characterised. The crystal structures for 1 and 3-7 have been solved and examined to elucidate if these structures are related to their decomposition. Thermogravimetric analysis was used to gain insight into the decomposition temperatures for each complex. Unlike previously explored metal xanthate complexes which break down at low temperatures (< 250 degrees C), to form crystalline metal chalcogenides, powder X-ray diffraction measurements suggest that when R >= Et these complexes did not produce crystalline gallium sulfides until heated to 500 degrees C, where gamma-Ga2S3 was the sole product formed. In the case of R = Me, Chugaev elimination did not occur and amorphous GaxSy products were formed. We conclude therefore that the low-temperature synthesis route offered by the thermal decomposition of metal xanthate precursors, which has been reported for many metal sulfide systems prior to this, may not be appropriate in the case of gallium sulfides.