Octahedral Hexanuclear Rhenium Cluster Dimers Bridged by Pyrazine or 4,4'-Bipyridine with 23- and 24-Electron Configurations.

New pyrazine (pz)- and 4,4'-bipyridine (4,4'-bpy)-bridged octahedral hexanuclear rhenium(III) cluster dimers, [{Re 6 (μ 3 -S) 8 Cl 5 } 2 (μ-L)] 6- (L = pz, [ 1 ] 6- ; L = 4,4'-bpy, [ 2 ] 6- ), with 2 × 24 d-electrons {Re 6 (24e)} 2 were obtained in a single-step reaction via photoirradiation of [Re 6 (μ 3 -S) 8 Cl 6 ] 4- with L in a 2:1 ratio at room temperature. The {Re 6 (23e)} 2 dimers, [{Re 6 (μ 3 -S) 8 Cl 5 } 2 (μ-L)] 4- (L = pz, [ 1' ] 4- ; L = 4,4'-bpy, [ 2' ] 4- ), were synthesized through two-electron oxidation of [ 1 ] 6- and [ 2 ] 6- , respectively. The single-crystal X-ray structures of [ 1 ] 6- and [ 1' ] 4- were determined, revealing structural distortion of the Re 6 core of [ 1' ] 4- due to the Jahn-Teller effect. The cyclic voltammograms of [ 1 ] 6- and [ 2 ] 6- showed two steps of one-electron redox processes attributable to Re 6 (23e)Re 6 (24e)/{Re 6 (24e)} 2 and {Re 6 (23e)} 2 /Re 6 (23e)Re 6 (24e), respectively. The separation between the two redox potentials is small (0.056 V for [ 1 ] 6- and 0.039 V for [ 2 ] 6- ). The magnetic susceptibilities of [ 1' ] 4- and [ 2' ] 4- were almost temperature-independent, with values of 2.98 and 2.85 μ B , respectively, indicating paramagnetism. These results suggest weak electronic interaction between two cluster units bridged by pz or 4,4'-bpy in the intercluster mixed valence state. The compounds [ 1 ] 6- and [ 2 ] 6- show photoluminescence in the near-infrared region at 296 K in the solid state.