Synthesis, crystal structure and properties of Mg3B36Si9C and related rare earth compounds RE3−xB36Si9C (RE=Y, Gd–Lu)

Na3MgB37Si9: an icosa-hedral B12 cluster framework containing {Si8} units

Single crystals of a novel sodium-magnesium boride silicide, Na3MgB37Si9 [a = 10.1630 (3) Å, c = 16.5742 (6) Å, space group R 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 inter-stitial site of the Dy2.1B37Si9-type structure with an occupancy of 0.5. The (001) layers of B12 icosa-hedra 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.