Probing hydrogen and halogen-oxo interactions in uranyl coordination polymers: a combined crystallographic and computational study

The syntheses and crystal structures of four compounds containing the UO22+ cation and either benzoic acid (1), m-chlorobenzoic acid (2), m-bromobenzoic acid (3), or m-iodobenzoic acid (4) are described and the vibrational spectroscopic properties for compounds 3 and 4 are reported. Single crystal X-ray diffraction analysis of these materials shows that uranyl oxo atoms are engaged in non-covalent assembly via either hydrogen (1 and 2) or halogen bonding (3 and 4) interactions. The halogen bonding in compounds 3 and 4 is notable as the crystallographic metric percentage of the sum of the van der Waals radii indicates these interactions are of similar strength. Characteristics of the halogen-oxo interactions of 3 and 4 were probed via Raman and infrared spectroscopy, which revealed significant differences in stretching frequency values for the two compounds. Additionally, compounds 3 and 4 were characterized via quantum chemical calculations and density-based quantum theory of atoms in molecules (QTAIM) analysis, which indicated that the I-oxo interaction in 4 is likely the stronger of the two interactions, with differences between the two interactions resulting from both inductive effects and halogen polarizability.