MgMn 4 Ga 18 : a novel three-shell gallium cluster structure.

The new ternary gallide MgMn 4 Ga 18 (magnesium tetramanganese octadecagallium) was synthesized and its crystal structure determined by means of single-crystal X-ray diffraction. The MgMn 4 Ga 18 structure can be described as that of a three core-shell cluster compound. The Mg atoms are surrounded by 16 adjacent Ga atoms, [MgGa 16 ], and the respective coordination polyhedron is an octadecahedron. This [MgGa 16 ] octadecahedron is encapsulated inside a [Ga 32 ] icohexahedron, which is in turn encapsulated inside a [Ga 40 ] pentacontaoctahedron. As a result, a three core-shell cluster, [MgGa 16 @Ga 32 @Ga 40 ], is identified. Electronic structure calculations were performed by means of the TB-LMTO-ASA program and additionally confirm the existence of the core-shell packing of the clusters.