Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds part VI Derivatives with Bidentate Ligands, Crystal Structures of tetrahedro‐ Decacarbonyl{μ‐[1,1‐bis(methylthio‐χS)ethane]}tetrairidium ([Ir4(CO)10‐(μ2‐(MeS)2CHMe)]), tetrahedro‐Tri‐μ‐carbonylheptacarbonyl{μ‐{ethylidenebis‐ [diphenylphosphine]‐χP:χP'}}tetrairidium ([Ir4(CO)10(μ2‐(Ph2P)2CHMe)]), and tetrahedro‐Tri‐μ‐carbonylheptacarbonyl{μ‐{propane‐1,3‐diylbis[diphenylphosphine]‐χP:χP'}}tetrairidium ([Ir4(CO)10(μ2‐Ph2P(CH2)3PPh2)])

The disubstituted clusters[Ir4(CO)10(μ2-LL)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (LL = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (LL = (Ph2P)2CHMe, cluste 2; LL =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1–3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.