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Type: Artigo de periódico
Title: Gas-phase nucleophilic reactions of Ge(OCH3)(4): experimental and computational characterization of pentacoordinated Ge anions
Author: Morgon, NH
Xavier, LA
Riveros, JM
Abstract: The gas-phase ion/molecule reactions of F- and CH3O- with Ge(OCH3)(4) have been investigated by Fourier transform ion cyclotron mass spectrometry. Both nucleophiles react preferentially by an addition mechanism to yield XGe(OCH3)(4)(-) (X = F, OCH3) complexes that are identified as typical pentacoordinated Ge species, Pentacoordinated Ge adducts formed with excess internal energy can undergo elimination of formaldehyde to yield HGe(OCH3)(4)(-) or further elimination processes that result in the formation of germyl anions like Ge(OCH3)(3)(-). Other minor product ions are also observed which can be attributed to the intermediacy of a pentacoordinated adduct. Dissociation of the XGe(OCH3)(4)(-) anions induced by infrared multiphoton excitation leads to sequential losses of formaldehyde and gives rise to different germyl anions like Ge(OCH3)(3)(-) HGe(OCH3)(2)(-), and H2GeOCH3-. The XGe(OCH3)(4)(-) and germyl anions react readily with BF3 through successive methoxide-fluoride exchange and this reaction provides a gas-phase synthetic pathway for multiply fluorinated Ge anions. Ab initio calculations performed on model pentacoordinated species Fn+1Ge(OH)(4-n)(-) (n = 0-4) reveal that addition of a fluoride ion on hydroxygermanes occurs preferentially in the apical position of a trigonal bipyramid. The fluoride affinity of the prototype molecule Ge(OH)(4) is calculated to be 60.9 kcal mol(-1), and fluoride affinity increases monotonically with increasing fluorine substitution, The fluoride affinity of GeF4 is calculated to be 79 kcal mol(-1). Similar calculations also predict an unusually high hydride affinity (60 kcal mol(-1)) for Ge(OH)(4) with the hydride occupying an equatorial position. (C) 2000 Elsevier Science B.V.
Subject: germanium methoxide
gas-phase nucleophilic reactions
pentacoordinated Ge anions
fluoride affinity
germyl anions
computational Ge chemistry
Country: Holanda
Editor: Elsevier Science Bv
Citation: International Journal Of Mass Spectrometry. Elsevier Science Bv, v. 195, n. 363, n. 375, 2000.
Rights: fechado
Identifier DOI: 10.1016/S1387-3806(99)00189-X
Date Issue: 2000
Appears in Collections:Unicamp - Artigos e Outros Documentos

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