Abstract
The structure of the weakly bound dimer of 1,1-difluoroethylene with vinyl fluoride was studied using Fourier-transform microwave spectroscopy in the 6-19 GHz range. In the observed dimer structure each monomer acts as both a weak bond donor and acceptor, giving a cyclic arrangement of C-H center dot center dot center dot F contacts. The difluoroethylene C=C bond is roughly perpendicular to the vinyl fluoride C=C bond, forming the cross of a T-shaped carbon atom framework, resembling the lowest energy structure predicted by MP2/6-311++G(2d,2p) calculations. Observed C-H center dot center dot center dot F distances are similar to those of vinyl fluoride and 1,1-difluoroethylene complexes with difluoromethane and HCCH. The dipole moment of the dimer was measured using the Stark effect, giving values of mu(a) = 0.9003(19) mu(b), = 0.030(8) D and mu(total) = 0.9008 (22) D. A second ab initio structure, with the C=C bonds in a slipped parallel arrangement, was predicted to be about 38 cm(-1) higher in energy than the T-shaped conformation. This higher energy arrangement has not been observed experimentally.. (C) 2017 Elsevier Inc. All rights reserved.