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Ab Initio Study of the Structural, Energetic, Bonding, and IR Spectroscopic Properties of Complexes with Dihydrogen Bonds

Ibon Alkorta and José Elguero

Instituto de Químicas Médica, CSIC, Juan de la Cierva, 3, 28006-Madrid, Spain

Otilia Mó and Manuel Yáñez*

Departamento de Química, C-9. Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain

Janet E. Del Bene*

Quantum Theory Project, University of Florida, Gainesville, Florida 32611, and Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555

J. Phys. Chem. A, 2002, 106 (40), pp 9325–9330

DOI: 10.1021/jp021159w

Publication Date (Web): September 14, 2002

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

The results of an ab initio study of complexes with X−H···H−M dihydrogen bonds are presented. The proton donors include HCCH and its derivatives HCCF, HCCCl, and HCCCN; HCN and its derivatives HCNLi⁺ and HCNNa⁺; CNH, and H₂O, and the proton acceptor is LiH. For comparison, selected complexes with NaH as the proton acceptor have also been investigated. The structures, binding energies and harmonic vibrational frequencies of all complexes were obtained at the MP2/aug‘-cc-pVTZ level of theory. The most stable complexes with C−H groups as proton donors are the cationic complexes NaNCH⁺:HLi and LiNCH⁺:HLi. These complexes exhibit very short H····H distances and are prototypical of dihydrogen-bonded complexes that may dissociate by eliminating H₂. The calculated binding energies correlate with the H···H distance, the elongation of the C−H donor bond, the amount of charge transfer into the H····H bonding region, and the charge density at the H···H bond critical point. As in conventional hydrogen-bonded complexes, the elongation of the proton donor C−H group correlates with the strength of the interaction, and with the red shift of the C−H stretching frequency. Although changes in the Li−H bond length do not follow a simple pattern, the Li−H stretching frequency is blue-shifted in the complexes.

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