J Comput Chem. 2016 Jan 05;37(1):130-42. doi: 10.1002/jcc.24207. Epub 2015 Oct 29.

Re-evaluation of the bond length-bond strength rule: The stronger bond is not always the shorter bond.

Journal of computational chemistry

Elfi Kraka, Dani Setiawan, Dieter Cremer

PMID: 26515027 DOI: 10.1002/jcc.24207

Abstract

A set of 42 molecules with N-F, O-F, N-Cl, P-F, and As-F bonds has been investigated in the search for potential bond anomalies, which lead to reverse bond length-bond strength (BLBS) relationships. The intrinsic strength of each bond investigated has been determined by the local stretching force constant obtained at the CCSD(T)/aug-cc-pVTZ level of theory. N-F or O-F bond anomalies were found for fluoro amine radicals, fluoro amines, and fluoro oxides, respectively. A rationale for the deviation from the normal Badger-type inverse BLBS relation is given and it is shown that electron withdrawal accompanied by strong orbital contraction and bond shortening is one of the prerequisites for a bond anomaly. In the case of short electron-rich bonds such as N-F or O-F, anomeric delocalization of lone pair electrons in connection with lone pair repulsion are decisive whether a bond anomaly can be observed. This is quantitatively assessed with the help of the CCSD(T) local stretching force constants, CCSD(T) charge distributions, and G4 bond dissociation energies. Bond anomalies are not found for fluoro phosphines and fluoro arsines because the bond weakening effects are no longer decisive.

© 2015 Wiley Periodicals, Inc.

Keywords: AsF and OF bonds; NCl; NF; PF; bond anomaly; bond length-bond strength relationships; local mode force constants

Publication Types

• Journal Article