Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH

Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH (AeGaTtH) have been investigated by means of inelastic neutron scattering (INS) and first principles calculations. The compounds contain separated Ga-H units being part of a two dimensional polyanionic layer, [TtGaH]^2- (Tt=Si, Ge, Sn). The INS spectra show internal Ga-H bending and stretching modes at frequencies around 900 and 1200 cm^-1, respectively. While the stretching mode is virtually invariant with respect to the variable chemical environment of the Ga-H unit, the bending mode frequency varies and is highest for BaGaSiH and lowest for BaGaSnH. The stretching mode is a direct measure of the Ga-H bond strength, whereas the bending mode reflects indirectly the strength of alkaline earth metal-hydrogen interaction. Accordingly, the terminal Ga-H bond in solid state AeGaTtH is distinct, but-compared to molecular gallium hydrides-very weak.