High-pressure Syntheses and Characterization of the Rare-earth Fluoride Borates RE2(BO3)F3 (RE=Tb, Dy, Ho)

The new rare-earth fluoride borates RE 2 (BO 3 )F 3 (RE=Tb, Dy, Ho) were synthesized under highpressure/ high-temperature conditions of 1:5 GPa=1200 °C for Tb 2 (BO 3 )F 3 and 3:0 GPa=900 °C for Dy 2 (BO 3 )F 3 and Ho 2 (BO 3 )F 3 in a Walker-type multianvil apparatus from the corresponding rareearth sesquioxides, rare-earth fluorides, and boron oxide. The single-crystal structure determinations revealed that the new compounds are isotypic to the known rare-earth fluoride borate Gd 2 (BO 3 )F 3 . The new rare-earth fluoride borates crystallize in the monoclinic space group P2 1 /c (Z = 8) with the lattice parameters a=16:296(3), b=6:197(2), c=8:338(2) Å , b =93:58(3)° for Tb 2 (BO 3 )F 3 , a= 16:225(3), b = 6:160(2), c = 8:307(2) Å , b = 93:64(3)° for Dy 2 (BO 3 )F 3 , and a = 16:189(3), b = 6:124(2), c = 8:282(2) Å , β= 93:69(3)° for Ho 2 (BO 3 )F 3 . The four crystallographically different rare-earth cations (CN=9) are surrounded by oxygen and fluoride anions. All boron atoms form isolated trigonal-planar [BO 3 ] 3- groups. The six crystallographically different fluoride anions are in a nearly planar coordination by three rare-earth cations.