A comparative study of some red- and blue-shifted linear H-bonded complexes of N2

Bond length changes, harmonic vibrational frequency shifts, and changes in the proton magnetic shielding of HX and HKrX (X = F, Cl) on complexation with N-2 to form the linear red-shifted N-2 ... HX and linear blue-shifted N-2 ... HKrX complexes were determined by ab initio computations, with and without counterpoise correction, at the SCF and MP2(full) levels of theory using a 6-311 ++G(2d,2p) basis set. The MP2 computations agree with predictions from a perturbation theory model involving the first and second derivatives of the interaction energy with respect to displacement of the H-X and H-Kr bond lengths from their equilibrium values in the isolated monomers. The theoretical results agree qualitatively with the experimentally observed frequency shifts, with near quantitative agreement for N-2 ... HKrCl The characteristic downfield shift of the isotropic proton magnetic resonance in the red-shifted complexes was obtained, but for the blue-shifted complexes, the proton NMR shifts to higher fields. (C) 2007 Wiley Periodicals, Inc.