Isoskeletal Rh10C2 metal clusters containing four Au(PPh3) groups and a variable number of carbonyl ligands

Abstract

The two new mixed-metal carbido-carbonyl clusters [Rh₁₀C₂(CO)₂₀{Au(PPh₃)}₄]1 and [Rh₁₀C₂(CO)_18^–{Au(PPh₃)}₄]2 have been obtained by reaction of K₂[Rh₁₂C₂(CO)₂₄] with [Au(PPh₃)Cl]. The two molecules are in equilibrium through the dissociation-association of two carbonyl ligands. Phosphorus-31 NMR solution spectra of both compounds are reported. The molecular structures of both 1 and 2 have been determined by single-crystal X-ray diffraction. The compounds are isomorphous and crystallize in the tetragonal system, space group P4₂/m, Z= 2; a=b= 15.446(3), c= 21.894(2)Å for 1. and a=b= 15.400(5), c= 21.801(5)Å for 2. The molecules contain a close-packed Rh₁₀C₂ bioctahedral core with the carbide atoms filling the cavities. Four Au(PPh₃) groups span triangular faces and the CO ligands cover the Rh₁₀ polyhedron conforming to a D_2h idealized molecular symmetry.