Triply hydrogen bonded van der Waals complexes: CH2F2?CF2CH2 and CH2F2?CF2CHF

The results of molecular beam Fourier transform microwave (FTMW) investigations of the van der Waals complexes of difluoromethane with 1,1-difluoroethene (DFE) and trifluoroethene (TFE) are reported. The rotational parameters of the complexes have been interpreted in terms of a C_s geometry with the two H or F atoms of CH₂F₂ lying out of the σ_v symmetry plane of the complexes. The complexes are bound by three hydrogen bonds, of which one is the stronger C-F?H-C type, and two are the weaker C-H?F?H-C or C-F?H?F-C types for DFM-DFE or DFM-TFE, respectively. The most notable difference in the two complexes is that the out of plane atoms are two hydrogens for DFM-DFE, but are two fluorines for DFM-TFE. Additional information on the structure and hydrogen bonding has been obtained from ab initio calculations.