Ligand competition on uranyl ion: further examples of zwitterionic vs. anionic carboxylate coordination

Abstract

Four uranyl ion mixed-ligand complexes involving anionic and zwitterionic carboxylate donors have been synthesized under solvo-hydrothermal conditions. [(UO₂)₂(pda)₂(bet)₂] (1), where pda²⁻ is 1,3-phenylenediacetate and bet is betaine, crystallizes as a monoperiodic coordination polymer in which all ligands are κ²O,O′-chelated and UO₂(pda)(bet)₂ units are decorating groups to the UO₂(pda) chain. In [bcebpH₂][UO₂(bcebp)(H₂O)₂][UO₂(tcenm)]₄·2H₂O (2), where tcenm³⁻ is tris(2-carboxylatoethyl)nitromethane and bcebp is 4,4′-bis(2-carboxylatoethyl)-4,4′-bipyridinium, the two ligands are separated into different polymeric units, di- (hcb) and monoperiodic, respectively, and hydrogen bonding of the bcebpH₂²⁺ counterions to chains results in heteropolycatenation, with the counterions crossing four hexagonal networks. [(UO₂)₂(pht)₂(bcpmb)] (3), where pht²⁻ is phthalate and bcpmb is 1,4-bis(4′-carbonylatopyridiniomethyl)benzene, is a diperiodic network with V₂O₅ topology, while [(UO₂)₄(O)₂(kpim)₂(bcpmb)] (4), where kpim²⁻ is 4-ketopimelate, is a diperiodic network with bis(μ₃-oxo)-bridged U₄O₂ secondary building units as nodes and sql topology. In this last case, the large size of the rings allows for 2D + 2D → 3D inclined polycatenation to occur. The relative strength of anionic and zwitterionic carboxylate donors and the importance of weak interactions in the structures are discussed.