NaB₅C: carbon insertion into a three-dimensional framework of boron octahedra leads to electron-precise cubic carbaborides

Abstract

The discussion of whether hexaborides need a minimum electronic stabilisation to exist or not, has now been enriched by the synthesis of NaB₅C, crystallising with the cubic CaB₆ structure.

References

1. M. v. Stackelberg and F. Neumann, Z. Phys. Chem. B, 1932, 19, 314.
2. P. Hagenmuller and R. Naslain, C. R. Acad. Sci., 1963, 257, 1294.
3. R. Naslain and J. Étourneau, C. R. Acad. Sci. Ser. C, 1966, 263, 484.
4. B. Albert, Angew. Chem., 1998, 110, 1135; Angew. Chem., Int. Ed. Engl., 1998, 37, 1117.
5. H. C. Longuet-Higgins and M. de V. Roberts, Proc. R. Soc. London, Ser. A, 1954, 224, 336.
6. Sodium (Merck, Darmstadt, p.a.) was refined by segregation and treated with boron (Chempur, Karlsruhe, 99.9+%) and graphite (Merck, Darmstadt) in a molar ratio of 6∶5∶1 at 1050 °C for 2 h in crucibles made of pyrolytic boron nitride, which were sealed in iron crucibles under helium by arc welding. The excess of sodium was removed by distillation at 10^–2 mbar and 400 °C. The starting materials and products were handled under argon.
7. A. C. Larson and R. B. Von Dreele, Program GSAS, Los Alamos, USA, 1985.
8. Crystal data: NaB₅C, cubic, space group Pm3̄m(221), a= 409.25(1) pm, V= 68.54 × 10⁶pm³, ρ_calc= 2.158 g cm^–3, Z= 1, µ= 2.1 mm^–1, 17 reflections, 3 refined positional and thermal displacement parameters (the boron and the carbon atom were refined with a common isotropic thermal displacement parameter), R_wp= 0.0877, R_p= 0.0677, χ²= 1.410, D_dw= 1.496, ρ_max/ρ_min= 0.854/–20.200 e Å^–3. Reflections which stem from a small excess of graphite were cut out of the powder diagram before refinement. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany (e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository number CSD-408930. Data were collected on a Huber powder diffractometer G645, with quartz monochromator, CuKα₁ radiation (λ= 1.54056 Å), flat-plate sample holder, measurement in transmission mode at 20.0(5)°C, 5 × 10^–5 mbar, step width 0.006°Θ, measurement range 3–50°Θ. CCDC 182/1040.
9. (a) P. Blum and F. Bertaut, Acta Crystallogr., 1954, 7, 81; (b) R. Naslain, J. Étourneau and P. Hagenmuller, in Boron and Refractory Borides, ed. V. I. Matkovich, Springer, Berlin, 1977, pp 262–292.
10. T. Ito, T. Kasukawa, I. Higashi and Y. Satow, Proc. 11th Int. Symp. Boron, Borides and Related Compounds, JJAP Series, 1994, 10, 11.
11. R. Hundt, Program KPLOT, Bonn, Germany, 1979.