AN APPROACH TO THE DESIGN OF MOLECULAR-SOLIDS - THE UREYLENEDICARBOXYLIC ACIDS

The crystal structures of a series of ureylenedicarboxylic acids have been determined as part of a project directed toward the design of molecular solids. The ureylenedicarboxylic acids were chosen for study because they were predicted to form a two-dimensional hydrogen-bonded network. This two-dimensional network is the result of two orthogonal linear arrays of self-complementary hydrogen-bonded functionalities, the dicarboxylic acids and N, N'-disubstituted ureas, being present in the same molecule. The simplest molecules of the series, 2,2'-ureylenediacetic acid (1), 3,3'-ureylenedipropionic acid (2), and 4,4'-ureylenedibutyric acid (3) as well as the simplest ureylene derived from a dipeptide, A, A'-carbonylbisglycylglycine (4) were synthesized and studied by using X-ray crystallographic techniques. Each molecule was found to crystallize to give the predicted solid-state structure. Two compounds, related to compound 3, were also studied, the methyl ester of 3, dimethyl 4,4'-ureylenedibutyrate (5), crystallizes to give a one dimensional network based only upon hydrogen bonds between the urea functionalities. The thiourea analogue of 3,4,4'-thioureylenedibutyric acid (6) forms a network based upon carboxylic acid hydrogen bonds, but there is no linear alignment of the thiourea functionality presumably due to the lower energy of hydrogen bonds to sulfur. © 1990, American Chemical Society. All rights reserved.