The First Alkaline‐Earth Fluorooxoborate Ba[B4O6F2]—Characterisation and Doping with Eu2

• Published in: Chemistry : a European journal 2018-01, Vol.24 (2), p.443-450
• Main Authors: Jantz, Stephan G., Pielnhofer, Florian, van Wüllen, Leo, Weihrich, Richard, Schäfer, Martin J., Höppe, Henning A.
• Format: Article
• Language: English
• Subjects: Barium; Beta rays; borate; Boron oxides; Chemistry; Crystal structure; Crystals; Diffraction; Emissions; Europium; Fluorine; NMR; Nuclear magnetic resonance; Optical properties; Single crystals; Solid state; X-ray diffraction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201704324

The very first alkaline‐earth fluorooxoborate Ba[B4O6F2] was synthesised by solid state methods starting from Ba(BF4)2, β‐BaB2O4, and B2O3. The crystal structure derived from single‐crystal X‐ray diffraction (P21/n, a=6.6384(2) Å, b=7.6733(3) Å, c=11.3385(4) Å, β=91.281(2)°, Z=4, Rint=0.0269, R1=0.018, wR2=0.034) comprises layers of BO3F tetrahedra condensed through triangular BO3 units according to the descriptor 2Δ2□: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. Weakly coordinating fluorooxoborates comprise BO3F tetrahedra condensed to triangular BO3 moieties, and are promising host structures for inorganic phosphors. Divalent europium on the barium site of this very first alkaline‐earth fluorooxoborate yielded an uncommon ultraviolet luminescence of broad‐band 5d→4f emission combined with narrow‐band 4f→4f emission of divalent europium.