Uranyl−Organic Frameworks with 1,2,3,4-Butanetetracarboxylate and 1,2,3,4-Cyclobutanetetracarboxylate Ligands

The reaction of uranyl nitrate with 1,2,3,4-butanetetracarboxylic acid (H4BTC) and 1,2,3,4-cyclobutanetetracarboxylic acid (H4CBTC) under hydrothermal conditions gives various two- and three-dimensional frameworks. The complex [(UO2)2(BTC)(H2O)4]·4H2O (1) is a (4,4) grid in which the BTC4− ligands act as rectangular nodes and the uranyl ions as divergent, side-defining nodes. Complexes [(UO2)2(CBTC)(H2O)2]·2H2O (2) and [(UO2)2(CBTC)(H2O)2]·H2O (3), with the ligand in the cis,trans,cis form, present two types of three-dimensional architectures, with narrow channels formed in complex 2 only. In complex 4, [H3O]2[(UO2)5(CBTC)3(H2O)6], the ligand is in the noncentrosymmetric trans,trans,trans form, which assumes a saddle shape. This peculiar geometry of the ligand results in the formation of two types of subunits: 4:4 (metal/ligand) metallacycles and 8:12 cubic boxes, which are connected to one another to form a cubic lattice containing large channels. This latter result shows that the same geometric consider...