H₂MBH₂ and M(μ-H)₂BH₂ Molecules Isolated in Solid Argon: Interelement M-B and M-H-B Bonds (M = Ge, Sn)

Laser-ablated boron atoms react with GeH₄ molecules to form novel germylidene borane H₂GeBH₂, which undergoes a photochemical rearrangement to the germanium tetrahydroborate Ge(μ-H)₂BH₂ upon irradiation with light of λ = 405 nm. For comparison, the boron atom reactions with SnH₄ only gave the tin tetrahydroborate Sn(μ-H)₂BH₂. 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(μ-H)₂BH₂ (M = Ge, Sn) two 3c-2e B-H-M hydrogen bridged bonds are formed by donation of electrons from the B-H σ-bonds into empty p-orbitals of M.