Harnessing the nominally terminal oxo atoms of the linear uranyl (UO<sub>2</sub><sup>2+</sup>) cation represents both a significant challenge and opportunity within the field of f-element hybrid materials. We have developed an approach for promoting oxo atom participation in a range of non-covalent interactions through judicious choice of strongly electron donating equatorial ligands and appropriately polarizable halogen-donor atoms. As such, we have generated a family of uranyl hybrid materials based on a combination of 2,5-dihalobenzoic acid and aromatic, chelating N-donor ligands. Delineation of criteria for oxo participation in halogen bonding interactions has been achieved by preparing materials containing 2,5-dichloro-, 2,5-dibromo-, or 2,5-diiodobenzoic acid coupled with 2,2’-bipyridine (bipy), 1,10-phenanthroline (phen), 2,2’:6’,2’’-terpyridine (terpy), or 4’-chloro-2,2’:6’,2’’-terpyridine (Cl-terpy)), which have been characterized via single crystal X-ray diffraction, Raman, Infrared (IR), and luminescence spectroscopy, as well as via electrostatic surface potential calculations. Raman and IR spectroscopy, and resulting stretching force constant calculations, show a weakening of the U=O bond, when oxo atoms are involved in halogen bonding with the 2,5-diiodobenzoic acid, whereas electrostatic surface potential calculations highlight the importance of halogen polarizability in leading to oxo participation in halogen bonding interactions. Our findings indicate that one route to promote oxo participation in halogen bonding on a consistent basis is the combination of strongly electron donating equatorial ligands paired with benzoic acid groups featuring multiple large, polarizable halogen atoms at the periphery.

Turning on the terminal: Promoting non-covalent interaction with uranyl oxo atoms

253rd National Meeting (2017)

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