Anion Recognition by Uranyl-Salophen Derivatives as Probed by Infrared Multiple Photon Dissociation Spectroscopy and Ab Initio Modeling

The vibrational features and molecular structures of complexes formed by a series of uranyl–salophen receptors with simple anions, such as Cl−, H−, and HCOO−, have been investigated in the gas phase. Spectra of the anionic complexes were studied in the $\tilde \nu $=800–1800 cm−1 range by mass‐selective infrared multiple photon dissociation (IRMPD) spectroscopy with a continuously tunable free‐electron laser. The gas‐phase decarboxylation of the formate adducts produces uranyl–salophen monohydride anions, which have been characterized for the first time and reveal a strong UH bond, the nature of which has been elucidated theoretically. The spectra are in excellent agreement with the results obtained from high‐quality ab initio calculations, which provided the structure and binding features of the anion–receptor complexes. Observing the unobserved: The vibrational features and molecular structures of complexes formed by a series of uranyl–salophen receptors with simple anions, such as Cl−, H−, and HCOO−, in the gas phase are described. The gas‐phase decarboxylation of the formate adducts produces uranyl–salophen monohydride anions, which reveal a strong UH bond (see figure).