MgMnGa: a novel three-shell gallium cluster structure.

The new ternary gallide MgMnGa (magnesium tetramanganese octadecagallium) was synthesized and its crystal structure determined by means of single-crystal X-ray diffraction. The MgMnGa structure can be described as that of a three core-shell cluster compound. The Mg atoms are surrounded by 16 adjacent Ga atoms, [MgGa], and the respective coordination polyhedron is an octadecahedron. This [MgGa] octadecahedron is encapsulated inside a [Ga] icohexahedron, which is in turn encapsulated inside a [Ga] pentacontaoctahedron. As a result, a three core-shell cluster, [MgGa@Ga@Ga], 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.