An 'old' rhodiumsulfide with surprising structure -: Synthesis, crystal structure, and electronic properties of Rh3S4

The reaction of rhodium with rhodium(III)-chloride and sulfur at 1320 K in a sealed evacuated quartz glass ampoule yields silvery lustrous, air stable crystals of the rhodiumsulfide Rh3S4 Although a sulfide of this composition was described in 1935 a closer characterization has not been undertaken. Rh3S4 crystallizes in a new structure type in the monoclinic space group C2/m with a = 1029(2)pm, b = 1067(1) pm, c = 621.2(8) pm, beta = 107.70(1)degrees Besides strands of edge-sharing RhS6 octahedra which are connected by S-2 pairs (S-S = 220 pm), the crystal structure of Rh3S4 contains Rh-6 cluster rings in chair conformation with Rh-Rh single bond lengths of 270 pm. Both fragments are linked by common sulfur atoms. Extended Huckel calculations indicate bonding overlap for both S-S- and Rh-Rh-interactions. Rh3S4 has a composition between the neighboring phases Rh2S3 and Rh17S15 and the structure combines typical fragments of both: RhS6-octahedra from Rh2S3 and domains of metal-metal bonds as found in Rh17S15. Rh3S4 is a metallic conductor, down to 4.5 It the substance shows a weak, temperature independent paramagnetism.