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(μ-S)Cl}(μ-L)] (L = pz, []; L = 4,4'-bpy, []), with 2 × 24 d-electrons {Re(24e)} were obtained in a single-step reaction via photoirradiation of [Re(μ-S)Cl] with L in a 2:1 ratio at room temperature. The {Re(23e)} dimers, [{Re(μ-S)Cl}(μ-L)] (L = pz, []; L = 4,4'-bpy, []), were synthesized through two-electron oxidation of [] and [], respectively. The single-crystal X-ray structures of [] and [] were determined, revealing structural distortion of the Re core of [] due to the Jahn-Teller effect. The cyclic voltammograms of [] and [] showed two steps of one-electron redox processes attributable to Re(23e)Re(24e)/{Re(24e)} and {Re(23e)}/Re(23e)Re(24e), respectively. The separation between the two redox potentials is small (0.056 V for [] and 0.039 V for []). The magnetic susceptibilities of [] and [] were almost temperature-independent, with values of 2.98 and 2.85 μ, 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 [] and [] show photoluminescence in the near-infrared region at 296 K in the solid state.