Four two-dimensional coordination polymers containing the uranyl cation (UO22+), (NH4)UO2(BDC)(1.5)center dot 2.5H(2)O (1), KUO2(NDC)(1.5)center dot 2H(2)O (2), [C(NH2)(3)]UO2(NDC)(1.5)center dot 2H(2)O (2b), and UO2(HBDC-Br)(2) (3) (BDC = 1,4-benzenedicarboxylate, NDC = 1,4-naphthalenedicarboxylate, BDC-Br = 2-bromoterephthalate) have been synthesized by hydrothermal reactions. Compounds 1-2b have the same honeycomb (6,3) net but with two-fold interpenetration in 1 and without interpenetration in 2 and 2b. The use of 2-bromoterephthalate yields compound 3 with a (4,4) net. The structures of 2 and 2b show that the interpenetration can be prevented by the addition of a bulky substituent to the ligand. Maintaining the desired topology, however, requires a careful choice of the substituent group. Compounds 1, 2, and 2b have a similar structural arrangement to that of benzenetricarboxylic acid (trimesic acid, H3BTC). In H3BTC, the six rings are formed by hydrogen bonding and the interpenetration is more complex than that in 1. Crystal data: 1, triclinic, space group P (1) over bar, a = 10.453(8) A, b = 12.316(9) A, c = 13.441(10) A, alpha = 78.49(1)degrees, beta = 82.17(1)degrees, gamma = 85.57(1)degrees, and Z = 4; 2, monoclinic, space group C2/c, a = 12.7795(9) A, b = 19.728(1) A, c = 15.379(1) A, beta = 92.247(1)degrees, and Z = 8; 2b, monoclinic, space group C2/c, a = 12.7214(8) A, b = 19.645(1) A, c = 17.065(1) A, beta = 98.896(1)degrees, and Z = 8; 3, monoclinic, space group P2(1)/c, a = 7.873(5) A, b = 18.358(14) A, c = 6.893(5) A, beta = 115.96(2)degrees, and Z = 2.