A Robust Thiourea Synthon for Crystal Engineering

Crystallographic characterization of a series of bis-thiourea derivatives derived from N,N'-bis(3-aminopropyl)piperazine revealed a highly conserved intramolecular hydrogen bonding pattern, with intramolecular S(6) [or, in one case, S(8)] hydrogen bonding interactions between each heterocyclic nitrogen atom and one proton of the adjacent propylthioureido substituent. These intramolecular hydrogen-bonding interactions lend an overall spiral-like structure to the molecules, rather reminiscent of the form of a spiral galaxy. These monomeric units assemble into infinite chains via the formation of intermolecular R(2)(2)(8) cyclic thiourea dimers, with the exception of a phenyl derivative, which crystallized as a monomeric bis(dimethyl sulfoxide) solvate. The S(6) intramolecular hydrogen bond motif was maintained in the phenylthioureido derivatives of both N-(3-aminopropyl)morpholine and 3,3'-diamino-N-methyl-dipropylamine. The robustness of the spiral galaxy motif and its apparent ability to direct intermolecular interactions suggest its potential utility as a useful new synthon for solid-state design.