LiEu[BO₃]: a lithium europium(II) <i>ortho-</i>oxoborate with a familiar crystal structure

Abstract Yellow, transparent single crystals of LiEu[BO 3 ] were obtained by serendipity in a solid-state reaction with the educts Eu 2 O 3 , MgBr 2 and Li[BH 4 ] at 750 °C within an arc-welded niobium ampoule enclosed in an evacuated fused silica secondary jacket. LiEu[BO 3 ] crystallizes isotypically to LiBa[BO 3 ] and LiSr[BO 3 ] in the monoclinic space group P 2 1 / n exhibiting the unit cell parameters a = 638.79(4) pm, b = 677.12(4) pm and c = 690.43(4) pm with a monoclinic angle of β = 110.648(3)° for Z = 4. Li + is coordinated by five oxygen atoms from three triangular planar [BO 3 ] 3– anions, while Eu 2+ has seven oxygen neighbors belonging to six ortho- oxoborate groups. A brief synopsis of the crystal structures of other Li M +II [BO 3 ] compounds is given and the Raman spectrum of LiEu[BO 3 ] compares well with the infrared spectrum obtained from the non-isotypic LiCa[BO 3 ].