Syntheses, Structures, and Comparisons of Heterometallic Uranyl Iodobenzoates with Monovalent Cations

The syntheses and crystal structures of six new heterometallic compounds containing the UO₂²⁺ cation, o-, m-, and p-iodobenzoic acid ligands, and Tl⁺, Rb⁺, and Cs⁺ cations which adopt the role of both charge balancing cation and secondary metal center are described, as are the luminescent properties for Tl⁺ containing compounds 1, 4, and 6. The structures of compounds 1-3 are isomorphous and contain uranyl monomers bound by o-iodobenzoic acid ligands with Tl⁺, Rb⁺, and Cs⁺ cations acting as secondary metal centers. Compounds 4 and 5 are also isomorphous and feature m-iodobenzoic acid ligands bound to the uranyl cation along with Tl⁺ and Rb⁺ cations. Compound 6 is unique in this series as it is assembled from a dimeric uranyl unit and features p-iodobenzoic acid ligands and Tl⁺ cations which function as charge balancing secondary metal centers. Single crystal X-ray diffraction analysis of these materials suggests that the secondary metal cations are incorporated based on the size of their ionic radius (Tl⁺ < Rb⁺ < Cs⁺), which is directly related to the size of the "pocket" observed in 1-6. Further, Voronoi-Dirichlet tessellation and Hirshfeld surface analysis were used to probe the coordination environment of the secondary metal centers as part of ongoing efforts to develop metrics for determining the coordination number of secondary metal cations in similar systems.