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ΒΒΓΕ112Ν2, trigonal, R3m (no. 166), a = 4.0728(3) Â, c = 26.589(3) A, V= 382.0 Â, Ζ = 3, Rgt(F) = 0.029, wRntfF) = 0.072, T= 293 K. Source of material Eu2[BN2]Br was synthesized from the mixture of EuN, J/-BN and Ε11ΒΓ2 in the molar ratio 2 : 1 : 1 : 1 . The finely ground reaction mixture transferred into a niobium ampoule, arc-welded and sealed in an evacuated silica tube was heated up to 1023 Κ within 8 h. After 24 h of annealing, the reaction ampoule was cooled down to room temperature during 8 h. Eu2[BN2]Br forms orange to pale yellow plate-like crystals, which are very sensitive to air and moisture. Therefore, all manipulations were performed under inert conditions in a glove box. For the single crystal investigation the specimens were encapsulated in glass capillaries. Experimental details The structure refinement with full occupancy factors for all atoms resulted in Äi = 0.036 and wR2 = 0.085 (Tables 2,3). While the equivalent atomic displacement parameters (ADP) for Eu and Br * Correspondence author (e-mail: hoehn@cpfs.mpg.de) atoms showed reasonable values of about 0.013(1) and 0.016( 1 ) Â, respectively, those for the boron position were unrealistically small, indicating the presence of stronger scattering power in this site. The nitrogen atom also revealed a slightly increased ADP value of 0.015(2) Â indicating a smaller contribution. Upon releasing of ADPs and site occupancies for both mentioned positions one obtained Ri = 0.032; w/?2 = 0.074 with ADPs of 0.010(4) Â and 0.013(2) Â and occupancies of 1.69(2) and 0.90(3) for Β and N, respectively. The results are compatible with a partial mutual substitution of [N-B-N] dumbells and the spherical Br units since both anions are possessing practically identical cationic environments (see crystal structure description). In the separate cycles of the refinement, the Β position was constrained to be mixed occupied by boron and bromine atoms (Tables 4,5). Utilizing the constrained values, the degree of disorder was estimated to be 5(2) %. Attempts to apply the same constraint for the Br position failed due to the large difference between the electron contribution of the heavy bromine and the light boron atoms in this site. Thus, we were not able to adapt completely the structure model describing the mutual replacement of Br~ and [BN2] units to our experimental data. However, the yellow color of the compound indicates that europium is still in its Eu state and the total composition of the compound has still to be regarded as Eu2[BN2]Br. Therefore, this model explains all structural pecularities, charge distribution, magnetic properties etc. in a satisfactory way. For the structure description we employed the ideal occupancy factors for Br, Β and Ν sites, as required by the ideal chemical composition Eu2[BN2]Br. Discussion The structure of the title compound is isotypic to Sr2[0-Cu-0]Br [1] and can be interpreted as a filled variant of the <znft°-NaCrS2 type of structure (S2CrNa) [2] with Eu, Br and Β at S, Cr and Na positions, respectively. The structure is characterized by layers of edge-sharing [N-B-N] @Eu6 and [Br]@Eu6 trigonal antiprisms (in other words distorted octahedra), which are alternately stacked along [001]. The bond lengths for the strictly linear [BN2]^ anions are d(B—N) = 1.354(8) Â, corresponding well with those observed for the other known isostoichiometric dinitrido-borate halides [3-5]. As for the hitherto known nitridoborate halides, the two differently shaped anions (rod-like [BN2]" and spherical Br~ in the crystal structure of Eu2[BN2]Br should be spatially well seperated from each other. The crystal structure refinement indicates, however, that a mutual replacement of the two moieties is possible. The disorder (ca. 5 %) appears to be reasonable since both units are embedded in the same cationic matrix built up by the condensed Eue trigonal antiprisms with the edge length within the triangle bases of4.073 Â and marginal differences of the antiprism heights: 4.381 Â ([BN2]) and 4.481 Â (Br"). Unauthenticated Download Date | 5/30/19 8:18 AM

Crystal structure of dieuropium(II) dinitridoborate bromide, Eu 2 [BN 2 ]Br