Lewis Acidic Behavior of MoOF₄ towards the Alkali Metal Fluorides in Anhydrous Hydrogen Fluoride Solutions

Previous studies performed on samples of MoOF₄ dissolved in anhydrous hydrogen fluoride (aHF) solutions have indicated the presence of the [Mo₂O₂F₉]^– anion. Building upon this earlier work, MoOF₄, and MF (M = Li–Cs) were dissolved in aHF solutions to produce M[Mo₂O₂F₉] (M = Li–Cs) salts. Structural analysis of the obtained compounds was performed using single-crystal X-ray diffraction. This study provides the first single crystal structures for the [Mo^VI ₂O₂F₉]^– anion. Additionally, IR and Raman spectroscopy were used to characterize each salt. These spectra were compared to calculated ones for the solid-state structure of each salt using the DFT-PBE0 density functional method. The calculated spectra were used to give band assignments in the experimentally obtained spectra.