Trimeric cyclamers: solution aggregation and high Z' crystals based on guest structure and basicity.

Ureidosalicylic acid forms remarkable trimeric cyclamer-like crystal structures with either three or six independent molecules in the asymmetric unit as a result of the excess of hydrogen bond donors and guest inclusion within the centre of the cyclamer. The structures persist in solution in hydrogen bond acceptor solvents suggesting a role for solution pre-association in forming high Z' structures.