Abstract

The title compounds Sr₂[BN₂]Br (1), Eu₂[BN₂]Br (2) and Eu₂[BN₂]I (3) were obtained from reactions of mixtures of Sr₃[BN₂]₂ and SrBr₂ (1) and the binaries EuN, h-BN and EuX₂ (X = Br, I) (2, 3), respectively. The crystal structure of Sr₂[BN₂]Br was solved from X-ray powder diffraction data and those of the europium compounds from X-ray single crystal data. Sr₂[BN₂]Br and Eu₂[BN₂]Br are isotypic crystallizing in the rhombohedral space group R-3m (No. 166, Pearson code: hR18; Z = 3; a = 4.11692(2) Å, c = 26.4611(2) Å (1); a = 4.0728(3) Å, c = 26.589(3) Å (2)). The crystal structures are built up by layers of condensed edge-sharing [B—N—B]@Eu₆ and [Br]@Eu₆ trigonal antiprisms, which are alternately stacked along [001]. Eu₂[BN₂]I – isotypic to Sr₂[BN₂]I – crystallizes in the monoclinic space group P2₁/m (No. 11, Pearson code: mP24; Z = 4; a = 10.2548(6) Å, b = 4.1587(3) Å, c = 13.1234(9) Å, β = 91.215(4)°). The crystal structure is characterized by slightly puckered layers formed by condensed edge sharing I@Eu₆ octahedra which are separated by isolated [BN₂]^3– units. The bond lengths for the strictly linear [BN₂]^3– anions in (1) and (2) are d(B—N) = 1.351(4) Å and 1.356(8) Å, respectively. In Eu₂[BN₂]I two crystallograhically distinct [BN₂]^3– anions are present with d(B1—N) = 1.32(4) Å, 1.37(4) Å and d(B2—N) = 1.30(4) Å, 1.34(4) Å, respectively. Their bond angles vary slightly: ∠(N—B1—N) = 179(3)° and ∠(N—B2—N) = 177(3)°. The magnetic susceptibility data of the europium compounds (2) and (3) indicate that the Eu ions are divalent with 4f⁷ configuration. Vibrational spectra were measured and interpreted based on the D_∞h symmetry of the discrete linear [N—B—N]^3– moieties, considering the site symmetry reduction and the presence of two distinct [BN₂]^3– groups in (3).