Dihydrogen bond: Difference between revisions

In [[chemistry]], a '''dihydrogen bond''' is a kind of [[hydrogen bond]], an interaction between a [[metal hydride]] bond and an OH or NH group or another [[proton]] donor. The first example of this phenomenon is credited to Brown and Heseltine.<ref>Brown, M. P.; Heseltine, R. W. "Co-ordinated BH3 as a proton acceptor group in hydrogen bonding" Chemical Communications 1968, page 1551-2. DOI: 10.1039/C19680001551</ref> They observed intense absorption bandsabsorptions in the [[IR spectroscopy|IR band]]s at 3300 and 3210 cm^-1 for a solution of (CH₃)₂NHBH₃. The higher energy band is assigned to a normal N-H vibration whereas the lower energy band is assigned to the same bond, which is interacting with the B-H. Upon dilution of the solution, the 3300 cm^-1 band increased in intensity and the 3210 cm^-1 band decreased, indicative of intermolecular association.

Interest in dihydrogen bonding was reignited upon the crystallographic characterization of the molecule [[ammonia borane|H₃NBH₃]]. In this molecule, like the one studied by Brown and Hazeltine, the hydrogen atoms on nitrogen have a partial positive charge, denoted H^&delta;+, and the hydrogen atoms on boron have a partial negative charge, often denoted H^&delta;-.<ref>A New Intermolecular Interaction: Unconventional Hydrogen Bonds with Element-Hydride Bonds as Proton Acceptor" Crabtree, R. H.; Siegbahn, P. E. M.; Eisenstein, O.; Rheingold, A. L.; Koetzle, T. F. ''Acc. Chem. Res.'' '''1996''', ''29(7)'', 348 - 354.</ref> In other words, the amine is a protic acid and the borane end is hydridic. The resulting B-H^...H-N attractions stabilize the molecule as a solid. In contrast, the related substance ethane, H₃CCH₃, is a gas with a boiling point 285 °C lower. Because two hydrogen atoms are involved, this is termed a dihydrogen bond.