We describe the synthesis of a new family of chlorinated Si-Ge hydrides based on the formula ClnH6-nSiGe. Selectively controlled chlorination of H3SiGeH3 is provided by reactions with BCl3 to produce ClH2SiGeH3 (1) and Cl2HSiGeH3 (2). This represents a viable single-step route to the target compounds in commercial yields for semiconductor applications. The built-in Cl functionalities are specifically designed to facilitate selective growth compatible with CMOS processing. Higher order polychlorinated derivatives such as Cl2SiHGeH2Cl (3), Cl2SiHGeHCl2 (4), ClSiH2GeH2Cl (5), and ClSiH2GeHCl2 (6) have also been produced for the first time leading to a new class of highly reactive Si-Ge compounds that are of fundamental and practical interest. Compounds 1-6 are characterized by physical and spectroscopic methods including NMR, FTIR, and mass spectroscopy. The results combined with first principles density functional theory are used to elucidate the structural, thermochemical, and vibrational trends throughout the general sequence of ClnH6-nSiGe and provide insight into the dependence of the reaction kinetics on Cl content in the products. The formation of 1 was also demonstrated by an alternative route based on the reaction of (SO3CF3)SiH2GeH3 and CsCl. Depositions of 1 and 2 at very low temperatures (380-450 degrees C) produce near stoichiometric SiGe films on Si exhibiting monocrystalline microstructures, smooth and continuous surface morphologies, reduced defect densities, and unusual strain properties.