Supramolecular structures of five 5-(arylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-triones: isolated molecules, hydrogen-bonded chains and chains of fused hydrogen-bonded rings.

In each of the five title compounds, namely 5-benzylidene-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C13H12N2O3, (I), 5-(3-methoxybenzylidene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C14H14N2O4, (II), 5-(4-methoxybenzylidene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C14H14N2O4, (III), 5-[4-(dimethylamino)benzylidene]-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C15H17N3O3, (IV), and 5-(3,5-di-tert-butyl-4-hydroxybenzylidene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione, C21H28N2O4, (V), which crystallizes with Z' = 2 in P-1, there is a very wide C-C-C angle at the methine C atom linking the two rings, ranging from 137.1 (2) degrees in (I) to 139.14 (14) degrees in (III). There is evidence for intramolecular charge separation in (IV) and, to a lesser degree, in (III). The molecules of (I)-(III) are linked by pairs of C-H...O hydrogen bonds into chains of edge-fused rings, with alternating R(2)2(14) and R(2)2(16) rings in (I), alternating R(2)2(14) and R(4)4(20) rings in (II), with two types of R(2)2(16) rings alternating in (III). The molecules in (IV) are linked by a single C-H...O hydrogen bond into simple C(8) chains, but there are no direction-specific intermolecular interactions in (V).