Strong Intra- and Intermolecular Aurophilic Interactions in a New Series of Brilliantly Luminescent Dinuclear Cationic and Neutral Au(I) Benzimidazolethiolate Complexes

The structural and photophysical properties of a new series of cationic and neutral Au(I) dinuclear compounds (1 and 2, respectively) bridged by bis(diphenylphosphino)methane (dppm) and substituted benzimidazolethiolate (X-BIT) ligands, where X = H (a), Me (b), OMe (c), and Cl (d), have been studied. Monocationic complexes, A(u2)(micro-X-BIT)(micro-dppm)(CF(3)CO(2)), were prepared by the reaction of A(u2)(micro-dppm)(CF(3)CO(2))(2) with 1 equiv of X-BIT in excellent yields. The cations 1a-1d possess similar molecular structures, each with a linear coordination geometry around the Au(I) nuclei, as well as relatively short intramolecular Au(I)...Au(I) separations ranging between 2.88907(6) A for 1d and 2.90607(16) A for 1a indicative of strong aurophilic interactions. The cations are violet luminescent in CH(2)Cl(2) solution with a lambda(em)(max) of ca. 365 nm, assigned as ligand-based or metal-centered (MC) transitions. Three of the cationic complexes, 1a, 1b, and 1d, exhibit unusual luminescence tribochromism in the solid-state, in which the photoemission is shifted significantly to higher energy upon gentle grinding of microcrystalline samples with DeltaE = 1130 cm(-1) for 1a, 670 cm(-1) (1b), and 870 cm(-1) (1d). The neutral dinuclear complexes, A(u2)(micro-X-BIT)(micro-dppm) (2a-2d) were formed in good yields by the treatment of a CH(2)Cl(2) solution of cationic compounds (1) with NEt(3). 2a-2d aggregate to form dimers having substantial intra- and intermolecular aurophilic interactions with unsupported Au(I)...Au(I) intermolecular distances in the range of 2.8793(4)-2.9822(8) A, compared with intramolecular bridge-supported separations of 2.8597(3)-2.9162(3) A. 2a-2d exhibit brilliant luminescence in the solid-state and in DMSO solution with red-shifted lambda(em)(max) energies in the range of 485-545 nm that are dependent on X-BIT and assigned as ligand-to-metal-metal charge transfer (LMMCT) states based in part on the extended Au...Au...Au...Au interactions.