Narrow Gap Semiconducting Germanium Allotrope from the Oxidation of a Layered Zintl Phase in Ionic Liquids

A metastable germanium
allotrope, Ge­(oP32), was synthesized as
polycrystalline powders and single crystals from the mild-oxidation/delithiation
of Li7Ge12 in ionic liquids. Its crystal structure,
from single crystal X-ray diffraction (Pbcm, a = 8.1527(4) Å, b = 11.7572(5) Å, c = 7.7617(4) Å), features a complex covalent network
of 4-bonded Ge, resulting from a well-ordered topotactic oxidative
condensation of [Ge12]7– layers. It is
a diamagnetic semiconductor (Eg = 0.33
eV), and transforms exothermically and irreversibly to α-Ge
at 363 °C. This demonstrates the potential of ionic liquids as
reactive media in the mild oxidation of Zintl phases to new highly
crystallized modifications of elements and simple compounds.