Crystal structure and fluxional behaviour in solution of [Rh-4(CO)(6)(mu-Me2PCH2PMe2)(3)]

[Rh-4 (CO)(6) (mu-Me2PCH2PMe2)(3)], the first example of a hexasubstituted derivative of Rh-4(CO)(12), has a ground state geometry in the solid state and in solution of C-s symmetry with four edge-bridging carbonyls and with each diphosphine ligand bridging one edge of the same Rh-3 face. The result is an imbalance of the formal electron count at two rhodium atoms. As observed by C-13- and P-31-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.