Matrix-isolation infrared studies of 1:1 molecular complexes containing chloroform (CHCl3) and Lewis bases: Seamless transition from blue-shifted to red-shifted hydrogen bonds

The infrared spectra of molecular complexes containing chloroform (CHCl3) and Lewis bases (N-2, CO, H2O, and CH3CN) have been observed in an Ar matrix, and vibrational peaks for the 1:1 complexes have been assigned. The C-H stretching band of chloroform in the complexes showed a seamless transition from a blue shift (for N-2 and CO) to a red shift (H2O and CH3CN), in accord with the proton affinity of the base molecules. Density functional calculations predicted that the C-H center dot center dot(sigma-type lone pair) isomer is the most stable, which is consistent with the observed vibrational peak shift upon complex formation. The underlying mechanisms of the C-H hydrogen bond were explored using the topological properties of the electronic charge density and natural orbital analyses. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730909]