RE4B4O11F2 (RE = Eu, Dy): New Phases Isotypic to the Fluoride Borate Gd4B4O11F2

The rare-earth fluoride borates RE 4 B 4 O 11 F 2 (RE = Eu, Dy) were synthesized in a Walkertype multianvil apparatus from the corresponding rare-earth oxides and fluorides, and boron oxide. Eu 4 B 4 O 11 F 2 was obtained under high-pressure/high-temperature conditions of 5 GPa and 900 °C, and Dy 4 B 4 O 11 F 2 at 8 GPa and 1000 °C. The single-crystal structure determinations revealed that both compounds are isotypic to Gd 4 B 4 O 11 F 2 , crystallizing in the space group C2/c (Z = 4) with the parameters a = 1368.2(3), b = 465.4(1), c = 1376.6(3) pm, β = 91.2(1)°, V = 0.8765(3) nm 3 , R1 = 0.0232, and wR 2 = 0.0539 (all data) for Eu 4 B 4 O 11 F 2 and a = 1349.5(3), b = 460.9(1), c = 1362.5(3) pm, β = 91.3(1)°, V = 0.8472(3) nm 3 , R1 = 0.0353, and wR 2 = 0.0729 (all data) for Dy 4 B 4 O 11 F 2 . These phases are entirely different from the recently discovered lanthanum fluoride borate La 4 B 4 O 11 F 2 , which exhibits the same constitution in another structure type with space group P2 1/c .