STERIC CONTROL OF SECONDARY, SOLID-STATE ARCHITECTURE IN 1/1 COMPLEXES OF MELAMINES AND BARBITURATES THAT CRYSTALLIZE AS CRINKLED TAPES

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.