Pentachlorocyclopropane/base complexes: matrix isolation infrared spectroscopic and density functional study of C-H- - -N hydrogen bonds.

Hydrogen-bonded complexes of pentachlorocyclopropane with the bases acetonitrile, ammonia, monomethylamine, and dimethylamine have been isolated and characterized for the first time in argon matrices at 16 K. Coordination of the proton of pentachlorocyclopropane (Pccp) to the electron donor (N) of the base was evidenced by red shifts of the CH stretching mode. These shifts, which range from 22 to 170 cm(-1), increase in the order CH3CN, NH3, (CH3)NH2, and (CH3)2NH. Density functional theory (DFT) calculations at the B3LYP level agree well with experiment and support the formation of 1:1 complexes of Pccp/base. Distinct changes were observed in ring modes as well as CCl and CCl2 modes. The hydrogen bond energy of the complexes varies from 2.95 to 4.22 kcal/mol and is stronger than our previously studied bromocyclopropane-ammonia complex (2.35 kcal/mol, MP2).