This paper describes the single-crystal X-ray structures of 1 : 1 complexes between seven N,N’-bis(4-X-phenyl)melamines (X = H, F, Cl, Br, I, CH3, and CF3) and 5,5-diethylbarbituric acid. These complexes crystallize as infinite tapes having components joined by triads of hydrogen bonds; the tapes pack with their long axes parallel. The crystalline architecture of these complexes-parallel tapes-serves as a structurally constrained framework with which to study physical-organic relationships between the structures of the crystals and the molecules of which they are composed. The complex with X = Br exists in polymorphic forms. One of the polymorphs is isomorphous to the X = Cl complex; the other is related to the X = I complex.