Coming to Grips with N−H···N Bonds. 1. Distance Relationships and Electron Density at the Bond Critical Point

TLDR: In this article, the geometry of N−H−N hydrogen bonds was optimized at the RHF/6-31G** level and the results for 67 species were reported.

Abstract: In an attempt to discover and analyze trends in distance relationships and properties at the bond critical point (BCP) in linear or near-linear N−H···N hydrogen bonds, the geometry of such bonds in a large number of suitable simple chemical species was optimized at the RHF/6-31G** level. The results for 67 of these are reported here; the geometry of 19 of them was optimized also at the MP2/6-31G** level. Correlations between the internuclear N−H, H···N, and N···N separations as well as between the N···BCP and H···BCP distances for these data sets and for different model functions are described in detail. The special case of symmetric N−H−N bonds is discussed; comparison with available experimental evidence shows that the correlation functions derived from the ab initio data have useful predictive value for crystallographic determinations involving short N−H−N bonds. Analysis of the correlation between the d(N−H) distance and the electron density ρc at the BCP has shown that although acceptable d,ρc repres...