Synthesis and crystal structure of MgB12Si2—The first ternary compound in the system B/Mg/Si

We report on the synthesis of MgB₁₂Si₂ the first ternary compound in the system B/Mg/Si. Yellow transparent single crystals were yielded from the elements at 1600 °C in h-BN crucibles welded in Ta ampoules. MgB₁₂Si₂ crystallizes orthorhombic in the space group Pnma with , , and Z=4. The crystal structure is characterized by layers of B₁₂ icosahedra, connected by isolated Si atoms to a three-dimensional framework. Mg atoms are placed in voids of the framework. Each icosahedron forms 8 B-Si bonds and 4 exohedral B-B bonds. The Si atoms are tetrahedrally coordinated by B atoms of the B₁₂ icosahedra.