Crystal structure and fluxional behaviour in solution of [Rh4(CO)6(mu-Me2PCH2PMe2)3]

[Rh4(CO)6(mu-Me2PCH2PMe2)3], the first example of a hexasubstituted derivative of Rh4(CO)12, has a ground state geometry in the solid state and in solution of Cs symmetry with four edge-bridging carbonyls and with each diphosphine ligand bridging one edge of the same Rh3 face. The result is an imbalance of the formal electron count at two rhodium atoms. As observed by 13C- and 31P-NMR, the mobility of the ligands is restricted to one mu-CO<-->eta-CO site exchange which astonishingly does not average dynamically the electron count on all four metal atoms.