Synthesis and characterization of dinuclear metal complexes with the P2S and As2S heteroatomic inorganic rings as bridging units. Crystal and molecular structure of [(triphos)Rh(As2S)Rh(triphos)](BPh4)2.cntdot.2(CH3)2CO [triphos = 1,1,1-tris((diphenylphosphino)methyl)ethane]