Study of the N-H center dot center dot center dot H-B dihydrogen bond including the crystal structure of BH3NH3 by neutron diffraction

Boraneamines tend to have close N-Hdelta+...delta-H-B contacts as a result of the intermolecular interaction of the NH proton with the BH bond by a no vel type of hydrogen bond (the dihydrogen bond). A CSD structural search pr ovides characteristic metric data for the interaction: the H ... H distance is in the range 1.7-2.2 Angstrom, and the N-H ... H group tends to be line ar 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. Wi th 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 ( d(HH) = 2.02 Angstrom).