Novel halogen bonding interactions between MH2 (M = Mg, Be) and HX (X = Cl, Br, I) molecules

In this work, a systematic theoretical investigation on a series of dimeric complexes formed between MH2 and FIX has been carried out by employing correlated ab initio methods. It was shown that besides dihydrogen bonds, there also exists novel noncovalent X center dot center dot center dot H interactions between the two molecules, which have similar characteristics to traditional halogen bonds. Upon complexation, the H-X bonds tend to elongate in all cases, concomitant with red-shifts of the H-X stretching frequencies. X center dot center dot center dot H interaction energies, calculated at the MP2/aug-cc-pvtz level, range from -2.11 to -11.78 kJ/mol; the interactions are much weaker than corresponding dihydrogen bonds. The major stabilization source of dihydrogen and halogen bonds arises from the electrostatic force, while charge-transfer force plays a minor role in the formation of the complexes. AIM analyses further confirm the presence of X center dot center dot center dot H interactions in the systems, and the electron density at bond critical points correlates fairly well with the interaction energy. (C) 2010 Elsevier B.V. All rights reserved.