Abstract
The control of molecular aggregation in the solid state is a current challenge in crystal engineering and materials chemistry. Supramolecular retrosynthesis via recurring synthons is an attractive strategy for the design and self-assembly of target crystal structures. This database study deals with occurrences of two- and three-point intermolecular C-H···O hydrogen bonded synthons in fragments of DAD, DDA and DDD type in organic crystals, where D=C( sp 2 )-H and A=O-atom. The number of hits with fragments DAD>DDA>>DDD (2606, 1485, 461 hits). Two-point recognition synthon DA⋅AD occurs more frequently in DAD and DDA structures (225, 111 hits) than DD⋅AA motif in DDA and DDD structures (34, 5 hits). Three-point recognition synthons DAD⋅ADA, DDA⋅AAD and DDD⋅AAA are extremely rare (3, 0, 1 hits). These frequency data are rationalised in terms of the molecular complexity of fragments, the overriding preference for centrosymmetric packing, and the stringent requirements of donor-acceptor and solubility match in binary crystals.
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