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) angstrom, b = 11.7572(5) angstrom, c = 7.7617(4) angstrom), features a complex covalent network of 4-bonded Ge, resulting from a well-ordered topotactic oxidative condensation of [Ge-12](7-) layers. It is a diamagnetic semiconductor (E-g = 0.33 eV), and transforms exothermically and irreversibly to alpha-Ge at 363 degrees 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.