Statistical analysis of C–H···N hydrogen bonds in the solid state: there are real precedents

Abstract

A survey of the Cambridge Structural Database reveals hundreds of C–H···N contacts which are significantly shorter (<2.45 Å) than the sum of the van der Waals radii (2.75 Å), effectively refuting recent claims to the contrary and supporting the description of this interaction as a hydrogen bond.

References

1. F. A. Cotton, L. M. Daniels, G. T. Jordan IV and C. A. Murillo, Chem. Commun., 1997, 1673.
2. M. Mascal, J. L. Richardson, A. J. Blake and W.-S. Li, Tetrahedron Lett., 1996, 37, 3505.
3. Version 5.13 (167 797 structures, April 1996 update): F. H. Allen and O. Kennard, Chemical Design Automation News, 1993, 8, 31.
4. Twenty-one entries with r values between 1.47 and 1.99 Å were found dubious and therefore not used in the final analysis. If the range is increased to r≤ 2.50 Å with 120 ≤α≤ 180°, a total of 1841 observations are found with r= 2.42 and ᾱ= 154°. An identical search involving neutron diffraction structures (in which all protons are accurately located) produces 13 observations with r̄= 2.43 Å(range 2.32–2.50 Å) and ᾱ= 150°(range 139–166°).
5. R. Taylor and O. Kennard, Acc. Chem. Res., 1984, 17, 320.
6. E. Weber, S. Franken, H. Puff and J. Ahrendt, J. Chem. Soc., Chem. Commun., 1986, 467.
7. R. Taylor and O. Kennard, J. Am. Chem. Soc., 1982, 104, 5063.
8. (C–)H atoms did however show a significant tendency to form close intermolecular contacts to oxygen (see also ref. 9). Due to the limited amount of data in this study, no real conclusions were drawn concerning C–H⋯N contact.
9. J. A. R. P. Sarma and G. R. Desiraju, Acc. Chem. Res., 1986, 19, 222; G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290.
10. M. H. Abraham, Chem. Soc. Rev., 1993, 22, 73.
11. A. Bondi, J. Phys. Chem., 1964, 68, 441; A recent revision of the van der Wasls radius of nitrogen to 1.60 Å would acually put the H to N contact distance at 2.80 Å(see S. C. Nyburg and C. H. Faerman, Acta Crystallogr., Sect. B, 1985, 41, 274), while the Pauling radius of N (1.5 Å) gives a total of 2.7 Å(see L. Pauling, The Nature of the Chemical Bond, Comell University Press, Ethica, 1942, p. 192).
12. The United Kingdom Chemical Database Service: D. A. Fletcher, R. F. McMeeking and D. Parkin, J. Chem. Inf. Comput. Sci., 1996, 36, 746.