Dihydrogen Bonds and Blue-Shifting Hydrogen Bonds: A Theoretical Study of AH•••HCF3 and TH2•••HCF3 Model Systems With A = Li or Na and T = Be or Mg

A theoretical study of the molecular properties of AH center dot center dot center dot HCF3 and TH2 center dot center dot center dot HCF3 (A = Li or Na and T = Be or Mg) model systems has been carried out at the B3LYP/6-311 + +G(3df,3pd) level of theory. Once the interactions between the proton donor (H+delta) of HCF3 and protonic hydrides (H-delta) have been produced, these systems appear, at first sight, to be dihydrogen-bonded complexes. Although a blue-shift was observed on the HC bond of HCF3 upon the formation of the BeH2 center dot center dot center dot HCF3 dihydrogen complex, in the case of LiH center dot center dot center dot HCF3,MgH2 center dot center dot center dot HCF3, and NaH center dot center dot center dot HCF3, however, a red-shift was detected on their HCF3 species. As far as B3LYP/6-311++G(3df,3pd) calculations are concerned, we have used the quantum theory of atoms in molecules to evaluate the molecular topography and charge density, according to which higher levels of charge transfer were computed on the red-shifted complexes. Finally, computation of Delta E-subset of dihydrogen bond energies revealed that vibrational red-shifts are observed in more strongly bonded complexes (values for Delta E-subset of ranging from 6.67 kJ mol(-1) to 19.66 kJ mol(-1)), whereas blue-shifts are found in weakly bonded ones (higher value for Delta E-subset of is 2.31 kJ mol(-1)). (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 307-316, 2010