Abstract
The compound Na(2)B(6)Si(2) was synthesized under high-pressure, high-temperature conditions at pressures ranging from 6 to 9.5 GPa and temperatures from 1070 to 1270 K before quenching to room temperature followed by slow decompression. The crystal structure was determined from microcrystals using precession-assisted electron diffraction tomography, validated by dynamical refinement and full-profile refinements using optimized coordinates from quantum chemical calculations (space group R3̅m, Pearson symbol hR30, a = 5.0735(1) Å and c = 16.0004(7) Å). The atomic arrangement consists of a unique framework formed by electron-precise octahedral closo (B(6))(2-) clusters connected via ethane-like (Si(2))(0) dumbbells. The Na(+) cations occupy cavities in the hierarchical variation of a Heusler-type framework. The balance (Na(+))(2)([B(6)](2-))(Si(0))(2) reveals an electron precise Zintl-Wade phase, which is in line with electronic band structure calculations predicting semiconducting behavior.