Symmetry constraints, molecular recognition and crystal engineering. Comparative structural studies of urea-butanedioic and urea-E-butanedioic acid (2:1) cocrystals

摘要

The crystal structures of two urea-dicarboxylic acid (2:1) cocrystals have been determined. Urea-butane-dioic acid forms monoclinic crystals, space group P2Jc (no. 14), with a = 5.637 (4), b = 8.243(3), c = 12.258(3)A, ? = 96.80(5)°, V = 565.6(8)A3, 2 = 2. Urea-2i-butenedioic acid also forms monoclinic crystals, space group P2l/c (no. 14), with a = 5.540(1), 4 = 8.227(1), c= 12.426(3) A, 0 = 97.22(3)°, 7 = 561.9(2)A3, Z = 2. The geometry and the conformation of both molecular aggregates and the three-dimensional networks formed are very similar. The two strongest hydrogen-bond interactions are constrained in the formation of the heteroaggregates, the third hydrogen-bond interaction is used to self-associate the heteroaggregates in one-dimensional chains, whereas the next three weaker hydrogen bonds interconnect the chains into well organized three-dimensional networks.