Study of the N−H···H−B Dihydrogen Bond Including the Crystal Structure of BH₃NH₃ by Neutron Diffraction

Boraneamines tend to have close N−Hδ+···δ-H−B contacts as a result of the intermolecular interaction of the NH proton with the BH bond by a novel type of hydrogen bond (the dihydrogen bond). A CSD structural search provides characteristic metric data for the interaction: the H···H distance is in the range 1.7−2.2 Å, and the N−H···H group tends to be linear while B−H···H tends to be bent. The reported X-ray structure of BH3NH3 seemed to provide a singular exception in having bent N−H···H and linear B−H···H. Our neutron diffraction structure of BH3NH3 now shows that the B and N atoms must be reversed from the assignment previously published. With the correct assignment we find the expected bent B−H···H and linear N−H···H arrangement in the closest intermolecular N−H···H−B interaction (dHH = 2.02 Å).