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, [Au-2-(mu-X-BIT)(mu-dppm)](CF3CO2), were prepared by the reaction of [Au-2(mu-dppm)](CF3CO2)(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)center dot center dot center dot Au(I) separations ranging between 2.88907(6) A for 1d and 2.90607(16) angstrom for la indicative of strong aurophilic interactions. The cations are violet luminescent in CH2O2 solution with a lambda(max)(em) of ca. 365 nm, assigned as ligand-based or metal-centered (MC) transitions. Three of the cationic complexes, la, 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 Delta E = 1130 cm(-1) for la, 670 cm(-1) (1b), and 870 cm(-1) (1d). The neutral dinuclear complexes, [Au-2(mu-X-BIT)(mu-dppm)] (2a-2d) were formed in good yields by the treatment of a CH2Cl2 solution of cationic compounds (1) with NEt3. 2a-2d aggregate to form dimers having substantial intra- and intermolecular aurophilic interactions with unsupported Au(I)center dot center dot center dot Au(I) intermolecular distances in the range of 2.8793(4)-2.9822(8) angstrom, compared with intramolecular bridge-supported separations of 2.8597(3)-2.9162(3) angstrom. 2a-2d exhibit brilliant luminescence in the solid-state and in DMSO solution with red-shifted A, lambda(max)(em) 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 center dot center dot center dot Au center dot center dot center dot Au center dot center dot center dot Au interactions.