Syntheses, crystal structures, magnetic properties and vibrational spectra of nitridoborate-halide compounds Sr2[BN2]Br and Eu2[BN2]X(X= Br, I) with isolated [BN2]3–units

Abstract

AbstractThe title compounds Sr2[BN2]Br (1), Eu2[BN2]Br (2) and Eu2[BN2]I (3) were obtained from reactions of mixtures of Sr3[BN2]2and 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 groupR-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]@Eu6and [Br]@Eu6trigonal antiprisms, which are alternately stacked along [001]. Eu2[BN2]I – isotypic to Sr2[BN2]I – crystallizes in the monoclinic space groupP21/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@Eu6octahedra which are separated by isolated [BN2]3–units. The bond lengths for the strictly linear [BN2]3–anions in(1)and(2)ared(B—N) = 1.351(4) Å and 1.356(8) Å, respectively. In Eu2[BN2]I two crystallograhically distinct [BN2]3–anions are present withd(B1—N) = 1.32(4) Å, 1.37(4) Å andd(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 4f7configuration. Vibrational spectra were measured and interpreted based on theD∞hsymmetry 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).