Steric control of secondary, solid-state architecture in 1:1 complexes of melamines and barbiturates that crystallize as crinkled tapes

Article abstract of DOI:10.1021/ja00089a019

This paper describes the single-crystal X-ray structures of four 1:1 complexes between N,N'-di(tert-butyl)melamine and 5,5-disubstituted barbituric acids (substituents = CH₂CH₃, CH₂CF₃, CH₃, and C₆H₅). These complexes crystallize as infinite 'crinkled' tapes having components joined by a triad of hydrogen bonds. The tapes are prevented from adopting a linear motif due to steric repulsion between tert-butyl groups on adjacent melamines; the crinkled motif avoids such repulsion. The tape backbones deviate from planarity to permit close packing of the crinkled tapes. Crystals of these complexes of a size and shape suitable for single-crystal X-ray diffraction analysis are readily grown; this system therefore seems well-suited for systematic study of the relationships between molecular and crystalline structure.