Ca₅₄In₁₃B_4–xH_23+x: A Complex Metal Subhydride Featuring Ionic and Metallic Regions

Reactions of CaH₂ with group 13 metals in a 1:1 Ca/Li flux mixture produce Ca₅₄In₁₃B_4–xH_23+x (2.4 < x < 4). This compound has a complex new structure [Im3̅, a = 16.3608(6) Å, Z = 2] which can be viewed as a body-centered cubic array of Bergman-related clusters that are composed of a central indium atom surrounded by an icosahedron of 12 calcium atoms; hydride ions cap each face, forming a pentagonal dodecahedron that is further surrounded by a calcium shell. These In@Ca₁₂@H₂₀@Ca₃₀ clusters are surrounded by a disordered calcium indium hydride network. Indium is not completely reduced by the flux; the structure features ionic hydride regions and metallic calcium indium regions, confirmed by electronic structure calculations and ¹H and ¹¹⁵In solid-state NMR spectroscopy. This compound can therefore be viewed as a “subhydride”, akin to the alkali metal suboxides that feature ionic oxide clusters surrounded by metallic regions.