PNNL

Abstract

Hydrogen bond (HB), first discussed in 1912, represents one of the most important research topics in modern chemistry.1-4 In a typical HB, a protonic hydrogen (HB donor) of an X–Hd+ bond (X is a highly electronegative atom, e.g., N, O, halogen) interacts with an adjacent lone pair of an electronegative atom (HB acceptor) in the X– Hd+···Ad- form.5 The HB acceptor Ad- could be a H atom when it is bonded to an electropositive atom such as boron or transition metal Y, this can result in a specific HB pattern, X–Hd+···Hd--Y, known as hydridic-to-protonic interactions.6 This interaction was first recognized as a real intermolecular N-H···H-B attraction in boraneammonia complexes in 1968,7 and the term “dihydrogen bond” (DHB) was coined in 1995 to describe such chemical bonding patterns,8, 9 eighty-three years later after the original HB concept was formulated. So far, DHB has attracted considerable attentions due to its involvements in comprehensive structural and energetic evolutions, as well as its major impact on reactivity and selectivity in both solution and the solid state.6, 10-16 For examples, DHB has manifested its crucial roles in broad and diverse fields such as molecular recognition,17 hydrogen storage materials,18 catalytic dehydrogenation,19, 20 synthetic chemistry,21 supramolecular selfassembly, 12, 22 and drug design.13,