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Acta Cryst. (2014). A70, C641
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Previous work from our group has focused on uranyl hybrid materials with para-substituted halogen benzoic acids.1 Applying a `cap and link' strategy we have successfully controlled the nuclearity of UO22+ in a series of coordination polymers and Ln3+ in a family of molecular materials.2,3 Here we have expanded on this strategy and produced a series of 12 unique uranyl hybrid materials. The hydrothermally synthesized complexes all feature bromo-substituted benzoic acid linkers and the UO22+ metal centers are capped with a chelating N-donor. Single crystal X-ray diffraction analyses of these materials allowed for the exploration of the structural relationship between the benzoic acid group and the chelating N-donor as well as the influence of pH on uranyl speciation. At an unadjusted pH (~3) a mix of molecular monomers and dimers are observed while at higher pH (5-6) molecular uranyl dimers are exclusively produced. A systematic study of the supramolecular interactions that governed extended solid-state assembly was investigated by varying the bromine position on the benzoic acid groups along with the chelating N-donor with pH. Assembly via halogen-halogen, halogen-π, π-π, and halogen-oxygen interactions was observed and the influence of these interactions on uranyl emission was also investigated. Solid-state luminescence and lifetime measurements were used to explore the effects of speciation and chelating N-donor ligands on the spectroscopic properties of the uranyl cation.

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