The First Alkaline‐Earth Fluorooxoborate Ba[B 4 O 6 F 2 ]—Characterisation and Doping with Eu 2+

The very first alkaline‐earth fluorooxoborate Ba[B 4 O 6 F 2 ] was synthesised by solid state methods starting from Ba(BF 4 ) 2 , β‐BaB 2 O 4 , and B 2 O 3 . The crystal structure derived from single‐crystal X‐ray diffraction ( P 2 1 / n , a= 6.6384(2) Å, b= 7.6733(3) Å, c= 11.3385(4) Å, β =91.281(2)°, Z= 4, R int = 0.0269, R 1 = 0.018, wR 2 = 0.034) comprises layers of BO 3 F tetrahedra condensed through triangular BO 3 units according to the descriptor 2Δ2□:<Δ2□>Δ. The extraordinary thirteen‐fold coordination of barium by oxygen and fluorine leads to interesting optical properties of a sample doped with divalent europium, where a 4f→4f emission was recorded around 359 nm together with a broad emission band of a 5d→4f emission peaking at 366 nm. The compound is further characterised by IR‐, Raman‐, and solid‐state NMR‐spectroscopic methods. Moreover, DFT calculations as well as TGA and DSC measurements were performed.