Na3MgB37Si9: an icosahedral B12 cluster framework containing {Si8} units

Abstract

Single crystals of a novel sodium–magnesium boride silicide, Na3MgB37Si9 [a = 10.1630 (3) Å, c = 16.5742 (6) Å, space group R\overline{3}m (No. 166)], were synthesized by heating a mixture of Na, Si and crystalline B with B2O3 flux in Mg vapor at 1373 K. The Mg atoms in the title compound are located at an interstitial site of the Dy2.1B37Si9-type structure with an occupancy of 0.5. The (001) layers of B12 icosahedra stack along the c-axis direction with shifting in the [–a/3, b/3, c/3] direction. A three-dimensional framework structure of the layers is formed via B—Si bonds and {Si8} units of [Si]3—Si—Si—[Si]3.