Systematic analysis of the probabilities of formation of bimolecular hydrogen-bonded ring motifs in organic crystal structures

A methodology has been developed for characterising hydrogen-bonded ring mo tifs formed between two organic molecules without any prior knowledge of th e topology or chemical constitution of the motifs. The method has been impl emented by modifying the current Cambridge Structural Database (CSD) System programs. All intermolecular ring motifs comprising less than or equal to 20 atoms formed with N-H ... N, N-H ... O, O-H ... N and O-H ... O hydrogen bonds in organic structures in the CSD have been classified. The 75 bimole cular motifs occurring in > 12 structures in the CSD are described in terms of their graph sets and chemical functionalities. Motifs are ranked accord ing to their frequency of occurrence and according to their probabilities o f formation, i.e. their frequency relative to the number of possible motifs which could have formed. These probabilities provide insights into the rel ative robustness of known and potential supramolecular synthons.