MoF₅ revisited. A comprehensive study of MoF₅

While the properties of molybdenum pentafluoride, MoF₅, have been investigated in the past, there exists no comprehensive study of the compound. Additionally, many of these studies appear incoherent and offer contradictory explanations of some of the observed properties of MoF₅. Consequently, a comprehensive examination of MoF₅ is presented here, including a redetermination of the crystal structure of MoF₅ using single crystal and powder X-ray diffraction, the reevaluation of its IR, Raman and UV–Vis spectrum, and a study of its density (3.50(2) g/cm³ @ 25 °C) and magnetic properties. Additionally, density functional theory (DFT) calculations were performed on the gas phase molecule Mo₄F₂₀ to provide a discussion of properties realized during investigation. Single crystal X-ray diffraction showed MoF₅ to crystalize in the monoclinic, C2/m space group, as isolated tetramers having the formula Mo₄F₂₀. Magnetic measurements showed that when “MoF₅” is cooled from the melt fast enough, paramagnetic species with S = ½ are present together with S = 0 species. These species may be described using the formula (MoF₅)_n (n = odd) and (MoF₅)_n (n = even, presumably n = 4). From the measurements, the content of the S = ½ species is estimated to be 6%. The preferred species of MoF₅ under ambient conditions is Mo₄F₂₀.