Two novel uranyl complexes of a semi-rigid aromatic tetracarboxylic acid supported by an organic base as an auxiliary ligand or a templating agent: an experimental and theoretical exploration

Two novel uranyl coordination polymers, namely, UO2(bptc)(H2bpy)·(bpy) (1) and (UO2)3(bptc)1.5(phen)2(H2O)2·H2O (2) (H4bptc = 3,3′,4,4′-benzophenonetetracarboxylic acid; bpy = 4,4′-bipyridine; phen = 1,10-phenanthroline), have been obtained via a hydrothermal method based on a semi-rigid aromatic tetracarboxylic ligand and two different auxiliary or templating N-containing ligands. Complex 1 shows a one-dimensional (1D) structure derived from double chains with two types of rings arranged alternately, which further exhibits an intriguing 3D supramolecular network induced by diverse non-covalent interactions. Complex 2 displays a dislocated “double floor” of a 2D structure (2D zigzag layers), in which the carboxylate groups of the bptc4− ligand adopt a variety of fascinating bridging modes. In addition, quantum chemical calculations were used to investigate the coordination properties and bonding nature of the as-synthesized complexes, and the results indicate that in these two complexes the 5f, 6d, and 7p orbitals of uranium and 2p orbitals of O and N atoms mainly contribute to the covalency of the U–O and U–N bonds.