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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|
|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 F(n+1)Ge(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.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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