Uranyl Carboxyphosphonates Derived from Hydrothermal in Situ Ligand Reaction: Syntheses, Structures, and Computational Investigations

Two uranyl carboxyphosphonates (H2dipy)[(UO2)3(H2O)2(H2DPTP)2]·2H2O (DPTP-U1) and (H2bbi)[(UO2)4(H2O)2(HDPTP)2] (DPTP-U2) [H6DPTP = 2,5-diphosphonoterephthalic acid, dipy = 4,4′-bipyridine, bbi = 1,1′-(1,4-butanediyl)bis(imidazole)] were synthesized under hydrothermal conditions. The carboxyphosphonate ligand was formed through the in situ oxidation of (2,5-dimethyl-1,4-phenylene)diphosphonic acid mediated by UO22+. Single-crystal X-ray diffraction analyses reveal that DPTP-U1 possesses uranyl carboxyphosphonate layers that are separated by protonated dipy cations. Whereas DPTP-U2 is in a three-dimensional framework structure with channels filled by protonated bbi cations. The computational investigations give an insight into the nature of bonding interactions between uranium(VI) and carboxyphosphonate ligand. The spectroscopic properties were also studied.