Octaflouridodirhenate(III) revisited: Solid-state preparation and quantum chemical calculations

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A simple method for the high-yield preparation of (NH4)2[Re2F8]·2H2O has been developed that involves the reaction of (n-Bu4N)2[Re2Cl8] with molten ammonium bifluoride (NH4HF2). Using this method, the new salt [NH4]2[Re2F8]·2H2O was prepared in ∼90% yield. The product was characterized in solution by ultraviolet–visible light (UV-vis) and 19F nuclear magnetic resonance (19F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re2F8]2– anion. The metal–metal bonding in the Re26+ unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re2Cl8]2– and [Re2Br8]2– analogues.