Uranyl-organic frameworks with 1,2,3,4-butanetetracarboxylate and 1,2,3,4-cyclobutanetetracarboxylate ligands

摘要

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)] center dot 4H(2)O (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)] center dot 2H(2)O (2) and [(UO2)(2)(CBTC)(H2O)2] center dot 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 considerations which have permitted the synthesis of uranyl-based molecular metallamacrocycles and boxes can be used for the design of porous three-dimensional frameworks based on analogous motifs.