title: Dipolar C[triple-bond]N...C[triple-bond]N interactions in organic crystal structures: database analysis and calculation of interaction energies.
abstract: The Cambridge Structural Database (CSD) has been used to study nonbonded interactions between dipolar cyano groups. The analysis shows that C[triple-bond]N...C[triple-bond]N interactions form in an analogous manner to those involving carbonyl groups, and with the same interaction motifs: a dominant antiparallel dimer (57.5%) together with smaller populations of perpendicular (19.4%) and sheared parallel (23.0%) motifs. Ab initio calculations using intermolecular perturbation theory (IMPT) show an attractive C[triple-bond]N...C[triple-bond]N interaction in the dominant antiparallel dimer, with E(t) = -20.0 kJ mol(-1) at d(C...N) = 3.30 A and with the motif having a shear angle close to 102 degrees . The antiparallel C[triple-bond]N...C[triple-bond]N interaction is therefore slightly weaker than the analogous C=O...C=O dimer (-23.5 kJ mol(-1)), but both interactions have attractive energies similar to that of a medium-strength hydrogen bond and, where sterically favoured, they are important in the stabilization of extended crystal structures.
authors.affiliation: Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 IEZ, England.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Wood
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Borwick
authors.forename: David J
authors.initials: DJ
authors.lastname: Watkin
authors.forename: W D Samuel
authors.initials: WD
authors.lastname: Motherwell
authors.forename: Frank H
authors.initials: FH
authors.lastname: Allen