The versatile nature of [ClAu(L–L)AuCl] (L–L=bis(diphenylphosphino)methane (dppm) or -butane (dppb)) in reactions with [Rh2Ru4(CO)16B]−: crystal structures of [{Rh2Ru4(CO)16B}2{μ-Au(dppb)Au}] and [RhRu4(CO)14B{Au(dppm)Au}]