Syntheses and structures of novel complex Yb(II) fluorides: YbBeF4, YbAlF5 and LiYbAlF6

Light green powder samples and single crystals of YbBeF₄, YbAlF₅, and LiYbAlF₆ have been prepared by heating appropriate mixtures of YbF₂ and BeF₂, YbF₂ and AlF₃, or YbF₂, LiF, and AlF₃ at 750 °C under argon in a closed silica ampoule. YbBeF₄ crystallises monoclinic with a = 667.4(2), b = 691.1(2), c = 640.2(2) pm, β = 103.87(2)°, YbAlF₅ crystallises tetragonal with a = 1380.3(3), c = 701.3(3) pm, and LiYbAlF₆ crystallises trigonal with a = 504.2(2) and c = 986.8(1) pm. YbBeF₄ is the first fluoroberyllate, which adopts the monazite type structure, YbAlF₅ is isotypic with BaTiF₅ and LiYbAlF₆ crystallises in the LiCaAlF₆ type structure. In all three fluorides the Yb atoms are in the oxidation state +2 and the Yb-F distances range from 232 to 280 pm. Measurements of the magnetic susceptibilities have shown that YbBeF₄, YbAlF₅ and LiYbAlF₆ are diamagnetic. The structures of YbBeF₄, YbAlF₅ and LiYbAlF₆ are discussed in comparison to the corresponding fluoroberyllates and -fluoroaluminates with Sr and Ca.