Superstructure formation in SrBa₈[BN₂]₆and 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.

Combining Nitridoborates, Nitrides and Hydrides—Synthesis and Characterization of the Multianionic Sr6N[BN2]2H3

“…Using the DMFIT program, values for the quadrupolar coupling constant (3.28 MHz) and the asymmetry parameter (0.05) were obtained as well as an isotropic chemical shift of 24.3 ppm [46] . Considering a N−B−N bond angle of 169.4°, these results fit nicely into the series of NMR parameters reported so far for nearly linear [BN 2 ] 3− units in other nitridoborates [24,47] …”

A Novel Nitridoborate Hydride Sr13[BN2]6H8 Elucidated from X‐ray and Neutron Diffraction Data

“…[16] The 11 B MAS NMR spectrum of the related compound SrBa 8 [BN 2 ] 6 published by Seidel et al provides another comparison. [32] As expected for the nearly linear structural motif of NÀ BÀ N, the quadrupole coupling constant is rather large, with values beyond 3 MHz, rarely observed in periodic solids. [33] In contrast, the asymmetry parameter is close to zero, reflecting the axial symmetry of the [BN 2 ] 3À ions, which are indeed perfectly linear in SrBa 8 [BN 2 ] 6 .…”

“…The 11 B MAS NMR spectrum of the related compound SrBa 8 [BN 2 ] 6 published by Seidel et al. provides another comparison [32] . As expected for the nearly linear structural motif of N−B−N, the quadrupole coupling constant is rather large, with values beyond 3 MHz, rarely observed in periodic solids [33] .…”

Li4Ba[BN2]2 – Structure and Vibrational Spectra

“…Combing an alkali and an alkaline earth cation leads to ordered phases, e.g. LiMg[BN 2 ], LiCa 4 [BN 2 ] 3 , or SrBa 8 [BN 2 ] 6 …”

“…LiMg[BN 2 ], [13] LiCa 4 [BN 2 ] 3 , [14] or SrBa 8 [BN 2 ] 6 . [15] Ordered nitridoborate structures are also known for two different anions. Typical examples are the nitridoborate nitride Ca 3 [BN 2 ]N [16] or the nitridoborate oxide Ba 4 [BN 2 ] 2 O.…”