Isolating equatorial and oxo based influences on uranyl vibrational spectroscopy in a family of hybrid materials featuring halogen bonding interactions with uranyl oxo atoms

The syntheses and crystal structures of six new complexes containing the UO₂²⁺ cation, m- or p-halobenzoic acid ligands (where halogens are Cl and I), and the chelating N-donors 1,10-phenanthroline (phen) (1, 3, 4, and 6) or 2,2':6',2''-terpyridine (terpy) (7 and 9) are described and compared to UO₂-m-bromo- and p-bromobenzoic analogues (2, 5, and 8) that have been reported previously. The spectroscopic properties (both vibrational and luminescence) for all nine complexes along with stretching and interaction force constants are reported and redshifts are noted as the electron-donating ability of the chelating N-donors increases. Single crystal X-ray diffraction analysis of these complexes shows that whereas inclusion of a chelating ligand (i.e. phen or terpy) in the uranyl first coordination sphere is important for limiting tecton diversity, variation of the position and identity of the halogen atom on the benzoic acid ligand exert much greater influence in terms of driving halogen bonding interactions with the uranyl oxo atoms. In particular, the polarizability of the selected halogen atom is shown to be the most important criterion for engineering oxo atom participation in noncovalent assembly. Spectroscopic analysis of complexes 1-9, however, demonstrates that vibrational spectra are impacted most by the degree of electron donation by equatorial N-donor ligands, and that in some cases, such donation may also facilitate oxo interactions with otherwise unfavorable halogen bond donors. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)