A new structure type of RE4B4O11F2: High-pressure synthesis and crystal structure of La4B4O11F2

The first lanthanum fluoride borate La4B4O11F2 was obtained in a Walker-type multianvil apparatus at 6 GPa and 1300 °C. La4B4O11F2 crystallizes in the monoclinic space group P21/c with the lattice parameters a=778.1(2) pm, b=3573.3(7) pm, c=765.7(2) pm, β=113.92(3)° (Z=8), and represents a new structure type in the class of compounds with the composition RE4B4O11F2. The crystal structure contains BO4-tetrahedra interconnected with two BO3-groups via common vertices, B2O5-pyroborate units, and isolated BO3-groups. The structure shows a wave-like modulation along the b-axis. The crystal structure and properties of La4B4O11F2 are discussed and compared to Gd4B4O11F2.