Periodic Trends Manifested through Gas-Phase Generation of Anions Such as [AlH4]-, [GaH4]-, [InH4]-, [SrH3]-, [BaH3]-, [Ba(0)(?2-O2CH)1]-, [Pb(0)H]-, [Bi(I)H2]-, and Bi- from Formates.
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ABSTRACT: 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(?-OCOH)4 - and Ga(?-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 -, generated from the formate adduct of lead formate, reductively eliminated H2 to form PbH-, in which Pb is in oxidation state zero. In the energy-minimized structure [H-Pb(?2-H2)]-, proposed as an intermediate for the process, a H2 molecule is coordinated with PbH- as a dihapto ligand. The formate adducts of strontium and barium produce monoleptic ions such as [M(0)(?2-O2CH)1]-, in which the formate ion is chelated to a neutral metal atom. The bismuth formate adduct undergoes a double reductive elimination process whereby the oxidation state of Bi is reduced from +3 to +1 and then to -1. Upon activation, the initially formed [H-Bi-H]- ion transforms to an anionic ?2-H2 complex, which eliminates dihydrogen to form the bismuthide anion (Bi-).
SUBMITTER: Zheng Z
PROVIDER: S-EPMC6641263 | biostudies-literature | 2018 Mar
REPOSITORIES: biostudies-literature
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