A significant proportion of the scientific community’s current knowledge of hydrogen bonding has been derived from crystal structure data. Research at the CCDC has investigated many aspects of hydrogen bonded interactions including; H-bond directionality at both the acceptor and at donor-H, the relationship between H-bond geometries and their interaction energies, resonance-assisted and resonance-induced H-bonding, the chemical and steric requirements for intramolecular H-bonding, and a general survey of motifs formed by strong intermolecular H-bonds. Importantly, CCDC research established that most short C-H•••Acceptor contacts were true H-bonds (Taylor & Kennard, 1985), a paper that settled a long-running dispute and has received nearly 2,000 citations in the ensuing years.
A substantial amount of research has also been done in the area of non-covalent contacts between dipolar groups. These types of interactions have been observed in small organic, metal-organic and in macromolecular structures. Orthogonal dipolar interactions between carbonyl groups have even been suggested to be important in the folding of some proteins and for the occurrence of some amino acid conformers in seldom occupied regions of Ramachandran space. As in the case of hydrogen-bonds, research at the CCDC has highlighted the complementarity between knowledge-based analysis and theoretical methods in determining preferred geometries and relative interaction propensities.
The focus of research is now turning to intermolecular interactions other than hydrogen bonds. These present major difficulties, not least because of variability in distances and directionality. Initial work in this area has focussed on Full Interaction Maps; contours generated over a whole molecule to probe the different regions of intermolecular "bonding". This work is very nascent but the goal is to develop it into a quantitative method for scoring polymorphs, taking account of all interactions.