UF ₄ and the High-Pressure Polymorph HP-UF ₄

A laboratory-scale synthesis of UF ₄ is presented that utilizes the reduction of UF ₆ with sulfur in anhydrous hydrogen fluoride. An excess of sulfur can be removed by vacuum sublimation, yielding pure UF ₄ , as shown by powder X-ray diffraction, micro X-ray fluorescence analysis, infrared and Raman spectroscopy, as well as magnetic measurements. Furthermore, a single-crystalline, high-pressure modification of UF ₄ was obtained in a multi-anvil press at elevated temperatures. The high-pressure polymorph HP-UF ₄ was characterized by means of single-crystal and powder X-ray diffraction, as well as by magnetic measurements, and presents a novel crystal structure type. Quantum-chemical calculations show the HP-modification to be 10 kJ mol ⁻¹ per formula unit higher in energy compared to UF ₄ .