Molecular Hydrogen as a Lewis Base in Hydrogen Bonds and Other Interactions.

Sławomir J Grabowski

doi:10.3390/molecules25143294

Abstract

The second-order Møller–Plesset perturbation theory calculations with the aug-cc-pVTZ basis set were performed for complexes of molecular hydrogen. These complexes are connected by various types of interactions, the hydrogen bonds and halogen bonds are most often represented in the sample of species analysed; most interactions can be classified as σ-hole and π-hole bonds. Different theoretical approaches were applied to describe these interactions: Quantum Theory of ‘Atoms in Molecules’, Natural Bond Orbital method, or the decomposition of the energy of interaction. The energetic, geometrical, and topological parameters are analysed and spectroscopic properties are discussed. The stretching frequency of the H-H bond of molecular hydrogen involved in intermolecular interactions is considered as a parameter expressing the strength of interaction.

Highlights

Three types of hydrogen bonds occur that differ in the character of the proton acceptor according to one of classifications [1,2]
The three centre–four electron (3c-4e) hydrogen bonds, marked as A-H···B, are characterised by a single atom centre proton donor (A), and one centre occurs for a proton acceptor (B) [3,4]
The complexes linked by the triel, magnesium, hydrogen, and chalcogen bonds are presented where the aluminum, magnesium, hydrogen, and sulphur atoms act as the Lewis acid centres, respectively, since they are in contact with the σ-electrons of dihydrogen

Summary

Introduction

Three types of hydrogen bonds occur that differ in the character of the proton acceptor according to one of classifications [1,2]. The O-H···O, N-H···O, C-H···N, and numerous other hydrogen bonds are commonly known as 3c-4e systems. The latter designation informs of three centres in the system: A, H, and B, and of four electrons attributed to them: a σ-bond (A-H) and a lone electron pair of the proton acceptor centre (B). For two other types of hydrogen bonds, the multicentre proton acceptor may be specified For one of these types, the π-electron systems play such a role [5]; acetylene or ethylene molecule and their derivatives as well as aromatic systems are examples of species that act as Lewis base units. The C-C σ-bonds may play a role of multicentre Lewis base sites, in cycloalkanes, for example [11,12,13]

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