In situ nitroso formation induced structural diversity of uranyl coordination polymers

Abstract

Four novel uranyl coordination polymers, UO₂(bcH₂ba)(bcNOba)_0.5 (1), UO₂(bcNOba)(H₂O) (2), UO₂(bcNOba)(phen) (3) and UO₂(bcH₂ba)₂[phen] (4) (H₂bcHba = 4,4′-(azanediylbis(methylene))dibenzoic acid; phen = 1,10-phenanthroline), were successfully synthesized through hydrothermal reactions. Interestingly, in situ nitrosylation of the secondary amine group was observed in the presence of nitric acid. This reactivity could serve as a platform for the synthesis of different novel uranyl coordination polymers. This work presents three possible pathways that could exist in the in situ reaction system. In compound 4, only the ligand that did not undergo in situ reaction (bcH₂ba⁻) was involved in the compound construction, in which the adjacent uranyl ions are bridged by two bcH₂ba⁻ ligands, and can be extended into a two-strand 1D chain structure. In compounds 2 and 3, only the ligand that underwent in situ reaction (bcNOba²⁻) participated in the compound build-up and the two compounds both featured 1D chain structures. Interestingly, ligands with and without in situ reaction both participated in the construction of compound 1 which possessed one uranyl ion, one bcH₂ba⁻ ligand and half a bcNOba²⁻ ligand, and could be further extended to a 3D porous helical framework. The 3D structure of compound 1 was defined by intertwining and interpenetrating six equivalent 3D porous helical frameworks. Structural analysis of these uranyl compounds revealed that the introduction of a nitroso group exerted significant influences on the conformations of ligands, skeletons and 3D structures. Furthermore, theoretical calculations using relativistic density functional theory were also performed to explore the electronic structure and bonding nature of these uranyl compounds.