High-pressure synthesis, crystal structure, and structural relationship of the first ytterbium fluoride borate Yb5(BO3)2F9

Yb5(BO3)2F9 was synthesized under high-pressure/high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C, representing the first known ytterbium fluoride borate. The compound exhibits isolated BO3-groups next to ytterbium cations and fluoride anions, showing a structure closely related to the other known rare-earth fluoride borates RE3(BO3)2F3 (RE=Sm, Eu, Gd) and Gd2(BO3)F3. Monoclinic Yb5(BO3)2F9 crystallizes in space group C2/c with the lattice parameters a=2028.2(4) pm, b=602.5(2) pm, c=820.4(2) pm, and β=100.63(3)° (Z=4). Three different ytterbium cations can be identified in the crystal structure, each coordinated by nine fluoride and oxygen anions. None of the five crystallographically independent fluoride ions is coordinated by boron atoms, solely by trigonally-planar arranged ytterbium cations. In close proximity to the above mentioned compounds RE3(BO3)2F3 (RE=Sm, Eu, Gd) and Gd2(BO3)F3, Yb5(BO3)2F9 can be described via alternating layers with the formal compositions “YbBO3” and “YbF3” in the bc-plane.