The patterns of water clusters within the Cambridge Structural Database have been classified as discrete rings and chains, infinite chains and tapes, and layer structures. Predominant patterns are found for discrete clusters as 4-membered water rings, and in chains with a repeat unit of 4 waters. In tapes dominant patterns consist of linked 5-membered rings sharing one edge, and alternate 4,6-membered rings sharing one edge. If donor/acceptor groups are included from the organic molecules then the discrete water patterns transform into the dominant tape motifs.

The probability of organic compounds crystallising as hydrates increases with increasing number of polar chemical groups in the molecule. The extended patterns of H-bonding involving chemical groups and water molecules have been studied and classified. The most frequent ring, chain, tape and layer patterns displayed between the water molecules alone in organic molecular crystals are also predominant patterns in the larger H-bond network when other donor/acceptors are included.

A database study of 34 770 accurate organic crystal structures reveals that the most important factor determining a higher frequency of hydrates is the sum of the average donor and acceptor counts for the functional groups. Different parameter forms for donor/acceptor properties were investigated for correlation with formation of hydrates, and are discussed. We did not find that the donor/acceptor ratio or the molecular weight significantly affects the hydrate formation. We also examined a wide range of calculated molecular properties and found that increasing polar surface is correlated with increasing hydrate formation. The water environment pattern of donor and acceptor hydrogen bonds in the crystal is influenced by the donor/acceptor ratio of the molecule.