Orthorhombic HP‐ RE OF ( RE = Pr, Nd, Sm – Gd) – High‐Pressure Syntheses and Single‐Crystal Structures ( RE = Nd, Sm, Eu)

High‐pressure modifications of the rare earth oxide fluorides RE OF ( RE = Pr, Nd, Sm – Gd) were successfully synthesized under conditions of 11 GPa and 1200 °C applying the multianvil high‐pressure/high‐temperature technique. Single crystals of HP‐ RE OF ( RE = Nd, Sm, Eu) were obtained making it possible to analyze the products by means of single‐crystal X‐ray diffraction. The compounds HP‐ RE OF ( RE = Nd, Sm, Eu) crystallize in the orthorhombic α ‐PbCl 2 ‐type structure (space group Pnma , No. 62, Z = 4) with the parameters a = 632.45(3), b = 381.87(2), c = 699.21(3) pm, V = 0.16887(2) nm 3 , R 1 = 0.0156, and wR 2 = 0.0382 for HP‐NdOF, a = 624.38(3), b = 376.87(2), c = 689.53(4) pm, V = 0.16225(2) nm 3 , R 1 = 0.0141, and wR 2 = 0.0323 for HP‐SmOF, and a = 620.02(4), b = 374.24(3), c = 686.82(5) pm, V = 0.15937(2) nm 3 , R 1 = 0.0177, and wR 2 = 0.0288 for HP‐EuOF. Calculations of the bond valence sums clearly showed that the oxygen atoms occupy the tetrahedrally coordinated position, whereas the fluorine atoms are fivefold coordinated in form of distorted square‐pyramids. The crystal structures and properties of HP‐ RE OF ( RE = Nd, Sm, Eu) are discussed and compared to the isostructural phases and the normal‐pressure modifications of RE OF ( RE = Nd, Sm, Eu). Furthermore, results of investigations by EDX and Raman measurements including quantum mechanical calculations are presented.