Probing the Influence of N‐Donor Capping Ligands on Supramolecular Assembly in Molecular Uranyl Materials

Abstract

AbstractThe syntheses and crystal structures of six new compounds containing the UO22+ cation, 3,5‐dichlorobenzoic acid, and a chelating N‐donor [2,2′‐bipyridine (bipy), 1,10‐phenanthroline (phen), 4,7‐dimethyl‐1,10‐phenanthroline (dimethylphen), 2,2′:6′,2″‐terpyridine (terpy), 4′‐chloro‐2,2′:6′,2″‐terpyridine (Cl–terpy), or 2,4,6‐tris(2‐pyridyl)‐s‐triazine (TPTZ)] are reported. Single‐crystal X‐ray diffraction analysis of these materials enabled the exploration of the structural relationship between the benzoic acids and the chelating N‐donor as well as providing a platform to evaluate the effects of ligand choice on uranyl hydrolysis and subsequent oligomerization. At an unadjusted pH (ca. 3), a mix of uranyl monomers and dimers are observed, dimer formation resulting from both bridging carboxylate linkers and hydroxo bridges. Assembly by halogen‐ and hydrogen‐bonding interactions as well as π–π interactions was observed depending on the experimental conditions utilized. Further, spectroscopic characterization (both vibrational and luminescence) of complexes 1, 4, and 5 to explore the effects of the electron‐donating ability of the capping ligand on the corresponding uranyl luminescence and vibrational spectra suggests that there is a relationship between the observed bathochromic shifts and the electron‐donating ability of the capping ligands.