Mg35Cu24Ga53: a three-dimensional cubic network composed of interconnected Cu6Ga6 icosahedra, Mg-centered Ga16 icosioctahedra, and a magnesium lattice.

Single-crystal X-ray structural determinations for the Mg(35.12(4))Cu24Ga(53.58(6)) and Mg(35.6(4))Cu24Ga(52.66(6)) refined compositions (Fdm, Z = 4) reveal empty (Cu,Ga)12 icosahedra and centered MgGa16 icosioctahedra that are interconnected at every vertex to a compact three-dimensional anion network. A small range of variable occupancy exists on one of three Ga and one of four Mg positions. The clusters are well-bonded and held in different sized cavities, in which they are also directly bonded to a Mg cation network. The two networks thus interpenetrate each other, and there are no spacers. The new phase is isostructural with K39In80, K17In41, and the electron-poorer Na35Cd24Ga56, all of which contain clathrate-II-type cation frameworks. Electron counting using the classic (MO-based) cluster assignments indicates that the refined structure is substantially ideal and closed-shell. The symmetry of the present structure does not suggest a ready conversion to an icosahedral quasicrystal or its approximants.