Li 2 Eu 3 Br 2 [BO 3 ] 2 : A New Europium(II) Halide Oxoborate with Yellow Luminescence

The europium(II) oxoborate Li 2 Eu 3 Br 2 [BO 3 ] 2 featuring lithium and bromide ions was synthesized by the reaction of Eu 2 O 3 with Li[BH 4 ] as lithium‐ and boron‐ as well as EuBr 3 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 R 3 m ( a = 1049.06(7) pm, c = 2993.1(3) pm, c/a = 2.853, Z = 12). The two crystallographically distinguishable Eu 2+ cations show either an eightfold coordination as bicapped trigonal prism ([EuO 6 Br 2 ] 12– ) or a ninefold coordination as monocapped square antiprism ([EuO 5 Br 4 ] 12– ). All oxygen atoms stem from isolated triangular [BO 3 ] 3– anions and the Li + cations reside in octahedral voids provided by both oxygen atoms and Br – anions.