Crystal Engineering with Bis(thiourea) Derivatives^†

Urea and thiourea functionalities, presenting opportunities for the formation of diverse hydrogen-bonded networks, represent powerful crystal engineering building blocks. Herein we report the synthesis and structural analysis of a series of meta-substituted aromatic bis(thiourea) derivatives in which the steric bulk of the aromatic group and of the thiourea side chains is systematically varied. Two limiting structural types are observed-cyclic dimers and extended three-dimensional network structures, with considerable variability within each of these classes. Incomplete cyclic dimers observed in some cases appear to represent structures transitional between these two limiting classes. Thiourea conformations, hydrogen-bonding parameters, and solid-state packing issues, each playing a role in the determination of preferred solid-state structure, are discussed in detail.