Li2Eu3Br2[BO3]2: A New Europium(II) Halide Oxoborate with Yellow Luminescence

The europium(II) oxoborate Li₂Eu₃Br₂BO₃]₂ featuring lithium and bromide ions was synthesized by the reaction of Eu₂O₃ with LiBH₄] as lithium- and boron- as well as EuBr₃ as bromide-source at 750 °C for 24 h in silica-jacketed sealed niobium capsules. The yellow, air-stable and yellow fluorescent compound crystallizes in the trigonal space group R3 m (a = 1049.06(7) pm, c = 2993.1(3) pm, c/a = 2.853, Z = 12). The two crystallographically distinguishable Eu²⁺ cations show either an eightfold coordination as bicapped trigonal prism (EuO₆Br₂]^12–) or a ninefold coordination as monocapped square antiprism (EuO₅Br₄]^12–). All oxygen atoms stem from isolated triangular BO₃]^3– anions and the Li⁺ cations reside in octahedral voids provided by both oxygen atoms and Br^– anions.