title: Superstructure formation in SrBa8[BN2]6 and EuBa8[BN2]6.
abstract: X-ray pure samples of SrBa8[BN2]6 and EuBa8[BN2]6 were synthesized from appropriate amounts of binary nitrides (Sr3N2, Ba3N2 and BN in sealed niobium ampoules and EuN, Ba3N2 and BN in BN crucibles, respectively) at temperatures up to 1370 K. The structure of SrBa8[BN2]6 was refined from single crystal X-ray diffractometer data: Fd3[combining macron]m, a = 1595.1(1) pm, wR(F(2)) = 0.0515, 387 F(2) values and 21 variables. EuBa8[BN2]6 has a lattice parameter of 1595.00(9) pm. Both nitridoborates adopt a new 2 × 2 × 2 superstructure variant of the LiCa4[BN2]3 type, realized through ordering of vacancies and Sr(2+) and Eu(2+) cations, respectively. The structures of SrBa8[BN2]6 and LiCa4[BN2]3 are related by a group-subgroup scheme. The Sr(2+)/vacancy ordering leads to an asymmetric coordination (1 × Sr(2+) and 8 × Ba(2+) in a distorted, mono-capped square prism) for the [BN2](3-) units with B-N distances of 132 and 136 pm. Vibrational spectra of SrBa8[BN2]6 and EuBa8[BN2]6 confirm the discrete linear [BN2](3-) units and (11)B solid state MAS NMR spectra are compatible with single crystallographic sites for the boron atoms. In EuBa8[BN2]6 the spectra are profoundly influenced by interactions of the (11)B nuclei with the unpaired electrons of the paramagnetic Eu(2+) ions.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany. pottgen@uni-muenster.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Seidel
authors.affiliation: Fachbereich Chemieingenieurwesen, Fachhochschule Münster, Stegerwaldstraße 39, 48565 Steinfurt, Germany. tj@fh-muenster.de.
authors.forename: Tobias
authors.initials: T
authors.lastname: Dierkes
authors.affiliation: Fachbereich Chemieingenieurwesen, Fachhochschule Münster, Stegerwaldstraße 39, 48565 Steinfurt, Germany. tj@fh-muenster.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Jüstel
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany. pottgen@uni-muenster.de and Institut für Physikalische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Benndorf
authors.affiliation: Institut für Physikalische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany and Institute of Physics in Sao Carlos, University of Sao Paulo, Sao Carlos, SP 13560-590, Brazil. eckerth@uni-muenster.de.
authors.forename: Hellmut
authors.initials: H
authors.lastname: Eckert
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany. pottgen@uni-muenster.de.
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen