Laser-ablated boron atoms react with GeH4 molecules to form novel germylidene borane H2GeBH2, which undergoes a photochemical rearrangement to the germanium tetrahydroborate Ge(mu-H)(2)BH2 upon irradiation with light of lambda = 405 nm. For comparison, the boron atom reactions with SnH4 only gave the tin tetrahydroborate Sn(mu-H)(2)BH2. Infrared matrix-isolation spectroscopy with deuterium substitution and the state-of-the-art quantum-chemical calculations are used to identify these species in solid argon. A planar structure of H2GeBH2 with an electron-deficient B-Ge bond with a partial multiple bond character (bond order = 1.5) is predicted by quantum-chemical calculations. In the case of M(mu-H)(2)BH2 (M = Ge, Sn) two 3c-2e B-H-M hydrogen bridged bonds are formed by donation of electrons from the B-H sigma-bonds into empty p-orbitals of M.