Lengthening of the N–H bond in N–H ⋯ N hydrogen bonds. Preliminary structural data and implications of the bond valence concept
Abstract
For N–H ⋯ N hydrogen bonds, the dependence of the N–H length on the H ⋯ N distance is studied using neutron diffraction data; this dependence is the same for both charged and uncharged N–H donors; geometry predictions for strong hydrogen bonds and values for the shortest possible N ⋯ N and N ⋯ O separations are deduced on the basis of the bond valence concept.