Na3[BN2] and Na2K[BN2]: A Known and a Novel Alkali Metal Dinitridoborate Obtained via Mild Thermal Dehydrogenation. Issue 2 (7th January 2014)

• Record Type: Journal Article
• Authors: Koz, Cevriye; Acar, Selçuk; Prots, Yurii; Höhn, Peter; Somer, Mehmet
• Is Part Of: Zeitschrift für anorganische und allgemeine Chemie. Volume 640:Issue 2(2014)
• Page Start: 279
• Page End: 285
• Publication Date: 2014-01-07
• Subjects: Ternary dinitridoborates -- Boron -- Nitrogen -- X‐ray diffraction -- Electronic spectroscopy -- Thermal analyses; Chemistry, Inorganic -- Periodicals; Chemistry -- Periodicals; 540
• DOI: 10.1002/zaac.201300445
• Languages: English
• ISSNs: 0044-2313

Abstract

Abstract: Na3 [BN2 ] and Na2 K[BN2 ] were obtained as white polycrystalline powders from the reaction of the respective binary mixtures NaNH2 :NaBH4 and NaNH2 :KBH4 in molar ratio 2:1 at 873 K and 683 K, respectively, in an argon stream. According to the results of thermal analysis measurements, both compounds are thermally stable only up to 954 K (Na3 [BN2 ]) and 712 K (Na2 K[BN2 ]), respectively, decomposing under evolution of alkali metal and nitrogen to yield hexagonal BN as final residue, which was identified from powder patterns. The crystal structure of Na3 [BN2 ] {β‐Li3 [BN2 ] type; P 21 / c (No. 14); Z = 4} was confirmed and the unit cell parameters redetermined: a = 5.724(1) Å, b = 7.944(1) Å, c = 7.893(1) Å, β = 111.31(1)°. According to X‐ray powder data, Na2 K[BN2 ] crystallizes isotypic to Na2 KCuO2 in the tetragonal space group I 4/ mmm (No. 139) with a = 4.2359(1) Å, c = 10.3014(2) Å and Z = 2. The crystal structure of Na2 K[BN2 ] is composed of linear [N–B–N] 3– anions centering elongated M 14 rhombic dodecahedra, which are formed by 8 sodium and 6 potassium atoms. The [BN2 ]@Na8/4 K6/6 polyhedra are stacked along [001] and condensed via common tetragonal faces to generate a space‐filling 3D arrangement. The B–N bond lengths for the strictly linear [N–B–N] 3– units are 1.357(4) Å. Vibrational spectra of the title compounds were measured and analyzed based on D ∞h symmetry of the relevant [N–B–N] 3– groups taking into account the site symmetry effects for Na3 [BN2 ]. Both the wavenumbers, as well as the calculated valence force constants f (B–N) = 7.29 N· cm –1 (Na3 [BN2 ]) and 7.33 N· cm –1 (Na2 K[BN2 ]), respectively, are in good agreement with those of the known alkali and alkaline earth dinitridoborates. Abstract :