Periodic Trends Manifested through Gas-Phase Generation of Anions Such as [AlH4]−, [GaH4]−, [InH4]−, [SrH3]−, [BaH3]−, [Ba(0)(η2-O2CH)1]−, [Pb(0)H]−, [Bi(I)H2]−, and Bi– from Formates

Metal-hydride anions of main group elements, such as BaH3– and InH4–, were generated by dissociating formate adducts of the respective metal formates. Upon activation, these adducts fragment by formate-ion ejection or by decarboxylation. For adducts of alkali-metal formates, the formate-ion ejection is the preferred pathway, whereas for those of alkaline-earth and group 13–15 metals, the expulsion of CO2 is the more favorable pathway. Decarboxylation is deemed to yield a metal–hydrogen bond presumably by a hydride transfer to the metal atom. For example, the decarboxylation of Al(η-OCOH)4– and Ga(η-OCOH)4– generated AlH4– and GaH4–, respectively. The initial fragment-ion with a H–M bond formed in this way from adducts of the heavier metals of group 13 (Ga, In, and Tl) undergo a unimolecular reductive elimination, ascribable to the “inert-pair” effect, to lower the metal-ion oxidation state from +3 to +1. As group 13 is descended, the tendency for this reductive elimination process increases. PbH3–, genera...