Abstract
The title compounds Sr~2~[BN~2~]Br (1), Eu~2~[BN~2~]Br (2) and Eu~2~[BN~2~]I (3) were obtained from reactions of mixtures of Sr~3~[BN~2~]~2~and SrBr~2~(1) and the binaries EuN, h-BN and Eu__X__~2~(X= Br, I) (2,3), respectively. The crystal structure of Sr~2~[BN~2~]Br was solved from X-ray powder diffraction data and those of the europium compounds from X-ray single crystal data. Sr~2~[BN~2~]Br and Eu~2~[BN~2~]Br are isotypic crystallizing in the rhombohedral space group__R__-3__m__(No. 166, Pearson code:hR__18;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]@Eu~6~and [Br]@Eu~6~trigonal antiprisms, which are alternately stacked along [001]. Eu~2~[BN~2~]I – isotypic to Sr~2~[BN~2~]I – crystallizes in the monoclinic space group__P__2~1~/m(No. 11, Pearson code:mP__24;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@Eu~6~octahedra which are separated by isolated [BN~2~]^3–^units. The bond lengths for the strictly linear [BN~2~]^3–^anions in(1)and(2)are__d(B—N) = 1.351(4) Å and 1.356(8) Å, respectively. In Eu~2~[BN~2~]I two crystallograhically distinct [BN~2~]^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 4__f__^7^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 [BN~2~]^3–^groups in (3).