Synthesis and Characterization of a Twin Cubane-Type Molybdenum−Rhodium−Sulfur Cluster, [{Mo₃RhCp*S₄(H₂O)₇(O)}₂]⁸⁺. X-ray Structure of [{Mo₃RhCp*S₄(H₂O)₇(O)}₂](CH₃C<su

The reaction of [Mo3S4(H2O)9]4+ (1) with [(Cp*RhCl2)2] afforded a novel rhodium−molybdenum cluster, [{Mo3RhCp*S4(H2O)7(O)}2]8+ (2). X-ray structure analysis of [2](pts)8·14H2O (pts- = CH3C6H4SO3-) has revealed the existence of a new oxo-bridged twin cubane-type core, (Mo3RhCp*S4)2(O)2. The high affinity of the Cp*Rh group for sulfur atoms in 1 seems to be the main driving force for this reaction. The strong Lewis acidity of the Cp*Rh group in intermediate A, [Mo3RhCp*S4(H2O)9]6+, caused a release of proton from one of the water molecules attached to the molybdenum atoms to give intermediate B, [Mo3RhCp*S4(H2O)8(OH)]5+. The elimination of two water molecules from two intermediate B molecules, followed by the deprotonation reaction of hydroxo bridges, generated the twin cubane-type cluster 2. The formal oxidation states of rhodium and molybdenum atoms are the same before and after the reaction (i.e., Mo(IV)3, Rh(III)). The Mo−O−Mo moieties in [2](pts)8·14H2O are nearly linear with a bond angle of 164.3(3)°, and the basicity of the bridging oxygen atoms seems to be weak. For this reason, protonation at the bridging oxygen atoms does not occur even in a strongly acidic aqueous solution. The binding energy values of Mo 3d5/2, Rh 3d5/2, and C 1s obtained from X-ray photoelectron spectroscopy measurements for [2](pts)8·14H2O are 229.8, 309.3, and 285 eV, respectively. The XPS measurements on the Rh 3d5/2 binding energy indicate that the oxidation state of Rh is 3+. The binding energy of Mo 3d5/2 (229.8 eV) compares with that observed for [1](pts)4·7H2O (230.7 eV, Mo 3d5/2). A lower energy shift (0.9 eV) is observed in the binding energy of Mo 3d5/2 for [2](pts)8·14H2O. This energy shift may correspond to the coordination of an oxygen atom having a negative charge to the molybdenum atom.