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

Abstract

Metal hydrides are an uprising compound class bringing up various functional materials. Due to the low X‐ray scattering power of hydrogen, neutron diffraction is often crucial to fully disclose the structural characteristics thereof. We herein present the second strontium nitridoborate hydride known so far, Sr13[BN2]6H8, formed in a solid‐state reaction of the binary nitrides and strontium hydride at 950 °C. The crystal structure was elucidated based on single‐crystal X‐ray and neutron powder diffraction in the hexagonal space group P63/m (no. 176), exhibiting a novel three‐dimensional network of [BN2]3− units and hydride anions connected by strontium cations. Further analyses with magic angle spinning (MAS) NMR and vibrational spectroscopy corroborate the presence of anionic hydrogen within the structure. Quantum chemical calculations reveal the electronic properties and support the experimental outcome. Sr13[BN2]6H8 expands the emerging family of nitridoborate hydrides, broadening the access to an open field of new, intriguing materials.

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] …”

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

“…The calculated electronic band structure (Figure S11, left) reveals a direct band gap of 4.1 eV, which agrees with the transparent and colorless appearance of Sr 6 N[BN 2 ] 2 H 3 . Similarly to the two other nitridoborate hydrides Sr 2 BN 2 H and Sr 13 [BN 2 ] 6 H 8 , the projected density of states (Figure S11, right) shows nitrogen at the top of the valence band with small contributions of Sr. [24,26] Interestingly, since both N and Sr states contribute to the top of the valence band, covalent interactions of N with Sr are indicated. This is also suggested by bond overlap population analysis (see SI) which indeed reveal considerable overlap between the isolated N 3À and Sr 2 + .…”

“…Two of the Sr ions show a distorted octahedral coordination by two hydride and four nitrogen anions (Figure 2b), whereas the third Sr is found inside a Sr(N 5 B 2 H 3 ) polyhedron, as previously seen in Sr 13 [BN 2 ] 6 H 8 . [24] The coordination sphere of the [BN 2 ] 3À units can be described as a bicapped trigonal prism (Figure 2c) which is also found in β-Ba 3 [BN 2 ] 2 . [30] The [BN 2 ] 3À unit itself is slightly bent with an NÀ BÀ N angle of 169.4(5)°and shows NÀ B bond lengths of 1.329(7)-1.353 (7) Å, which are in good agreement with other known nitridoborates.…”

“…Nitridoborate hydrides containing complex [NÀ BÀ N] 3À ions are another emerging group of structurally intriguing salt-like metal hydrides. [24] Starting with Ca 2 BN 2 H in 2004, this class combines highly stable nitridoborate ions next to the elusive hydride ions within one material. [25][26] When it comes to multinary compounds with three or more different anions, the hydride family is only sparsely explored yet, with SmH 0.78 OF 0.22 and Sr 2 LiHOCl 2 being just two recent members.…”

“…[48] Hydride in-plane and out-of-plane vibrations, in which the hydride ion vibrates inside its strontium coordination sphere, can be observed at 919, 815 and 697 cm À 1 , agreeing with literature. [24][25] The weak band at 1725 cm À 1 is caused by NÀ BÀ N vibrations of the side phase Sr 3 B 2 N 4 . Furthermore, any OH or NH species can be excluded, as there are no vibrations visible in the region of 3600-3200 cm À 1 (Figure S3).…”