The role of C-H•••O interactions in the solid and liquid-phase structures of methyltrioxo rhenium

The importance of C-H center dot center dot center dot O hydrogen bonds involving the less common Re=O acceptor group in the small organometallic methyltrioxorhenium (MTO) is studied by combined vibrational spectroscopy and ab initio calculations. The observed vibrational spectrum is well described by the calculated spectrum of a C-H center dot center dot center dot O bonded dimer, which accounts for the symmetry decrease and the intermolecular interactions in the solid. Spectral evidence indicates both C-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds are formed in the MTO/methanol solutions. The Re=O stretching mode is sensitive to hydrogen bonding, but the major effects of intermolecular association are observed in the PC-H and vC-H modes of MTO. Ab initio calculations for the MTO/methanol system predict the coexistence of both the Lewis adduct and the hydrogen-bonded complex, with an energy difference of ca. 1.2 kJ(.)mol(-1). (c) Wiley-VCH Verlag GmbH & Co.