The Short N−F Bond in N2F+ and How Pauli Repulsion Influences Bond Lengths. Theoretical Study of N2X+, NF3X+, and NH3X+ (X = F, H)

F.M. Bickelhaupt, R.L. DeKock, E.J. Baerends

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Exceptionally short N−F bond distances of only 1.217 Å (crystal) and 1.246 Å (gas phase) have been reported for N2F+, making it the shortest N−F bond ever observed. To trace the origin of this structural phenomenon, we have analyzed the model systems N2X+, NF3X+, and NH3X+ (X = F, H) using generalized gradient approximation density functional theory at BP86/TZ2P. In good agreement with experiment, the computations yield an extremely short N−F bond for N2F+:  we find N−F bond distances in N2F+, NF4+, and NH3F+ of 1.245, 1.339, and 1.375 Å, respectively. The N−X bonding mechanisms are quantitatively analyzed in the framework of Kohn−Sham MO theory. At variance with the current hypothesis, reduced steric and other Pauli repulsion (of substituents or lone pairs at N with F) rather than the extent of s−p hybridization of N (i.e., sp versus sp3) are responsible for the much shorter N−F distance in N2F+ compared to NF4+. The results for our nitrogen compounds are furthermore discussed in the more general context of how bond lengths are determined by both bonding and repulsive orbital interactions.
Original languageEnglish
Pages (from-to)1500-1505
Number of pages6
JournalJournal of the American Chemical Society
Issue number7
Publication statusPublished - 2002


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