Infrared spectra and structures of the stable CuH(2)(-), AgH(2)(-), AuH(2)(-), and AuH(4)(-) anions and the AuH(2) molecule.

Gold is noble, but excited gold is reactive. Reactions of laser-ablated copper, silver, and gold with H(2) in excess argon, neon, and pure hydrogen during condensation at 3.5 K give the MH molecules and the (H(2))MH complexes as major products and the MH(2)(-) and AuH(4)(-) anions as minor products. These new molecular anions are identified from matrix infrared spectra with isotopic substitution (HD, D(2), and H(2) + D(2)) and comparison to frequencies calculated by density functional theory. The stable linear MH(2)(-) anions are unique in that their corresponding neutral MH(2) molecules are higher in energy than M + H(2) and thus unstable to M + H(2) decomposition. Infrared spectra are observed for the bending modes of AuH(2), AuHD, and AuD(2) in solid H(2), HD, and D(2), respectively. The observation of square-planar AuH(4)(-) attests the stability of the higher Au(III) oxidation state for gold. The synthesis of CuH(2)(-) in solid compounds has potential for use in hydrogen storage.