GeX2.dioxane (X = Cl, Br) complexes insert completely into CBr4 to afford the sterically crowded cluster compounds (BrCl2Ge)(4)C (1) and (Br3Ge)(4)C (2) in 80% and 95% yields, respectively. These display physical, spectroscopic, and structural properties that are indicative of highly symmetric molecules with a remarkably strained carbon center. Compounds 1 and 2 react with LiAlH4 to produce the hydrides (H-3 Ge)(3)CH (3) and (H3Ge)(4)C (4) which an readily identified and characterized by spectroscopic methods and gas-phase electron diffraction. Compound 3 is also conveniently prepared from the LiAlH4 reduction of (GeBr3)(3)CH (5) which in turn is obtained by insertion of GeBr2.dioxane into the C-Br bonds of bromoform. Refinement of the diffraction data for 3 confirmed a model of C-3 symmetry, with local (3 upsilon) symmetry of the GeH3 groups, and gave a Ge-C bond length of 1.96 Angstrom. The structure refinement of 4 was based on a model of T symmetry and displayed a rather normal Ge-C bond distance of 1.97 Angstrom, which is substantially shorter than that (2.049 Angstrom) of the strained (Br3Ge)(4)C (2) compound. Density functional calculations closely reproduced the observed molecular structures for 3 and 4. The thermal dehydrogenation of 4 on (100) Si surfaces at 500 degrees C resulted in the growth of a diamond-structured material with an approximate composition of Ge4C. Reactions of 4 with (SiH3)(2) on Si yielded heteroepitaxial growth of metastable, monocrystalline (Ge4C)(x)Si-y alloy semiconductors that are intended to have band gaps wider than those of pure Si and Si1-xGex alloys and strained superlattices. The covalent cluster species described here not only are of intrinsic molecular interest but also provide a unique route to a new class of semiconductor materials and form a model for local carbon sites in Ge-C crystals and related electronic materials based on the diamond structure.