Ba10LuB18O32F13: the first example of borate in the Lu–B–O–F system with the unprecedented FBB [B9O22]

A new alkaline-earth and rare-earth borate fluoride, Ba10LuB18O32F13, the first example of borate in the Lu–B–O–F system, has been successfully synthesized in a high-temperature vacuum system. It crystallizes in the orthorhombic system, with the Fmm2 space group and the parameters a = 16.5749(6) Å, b = 16.7644(9) Å, c = 13.6222(6) Å, and Z = 4. It represents a new fundamental building block (FBB), [B9O22], with the notation 9:[2(4:2Δ + 2T) + T], in which two [BO3] triangles and two [BO4] tetrahedra are enclosed into a [B4O10] ring and every two [B4O10] rings are bridged by a [BO4] tetrahedron. The [B9O22] FBBs are further condensed into a 3D network with two types of channels that accommodate Ba2+ and Lu2+ cations. The UV cut-off edge is below 190 nm, indicating the application potential of Ba10LuB18O32F13 in the DUV region. Additionally, to further explore the structural novelty of Ba10LuB18O32F13, a comparison with all anhydrous borates with 18 boron atoms in their chemical formula was carried out. The fascinating results indicate that [B9O22] has been discovered for the first time, enriching borate fluoride structure chemistry.