Gaseous germyl cations: A theoretical investigation on the structure, properties, and mechanism of formation of [formula omitted] and [formula omitted] (n = 0–2)

Abstract

The six germyl cations FnGe(OH)3-n+ and FnGe(NH2)3-n+ (n=0–2), recently observed in the gas phase from the cascade reactions between GeF3+ and H2O or NH3 (J. Mass Spectrom. 46 (2011) 465–477), were theoretically investigated by MP2 and CCSD(T) calculations. The bond distances and the electronic properties of these ions, and the stabilities of their complexes with H2O, NH3, and HF are regularly affected by the nature of the substituents. In particular, any Ge–X bond (X=F, OH, NH2) becomes progressively shorter by increasing the electronegativity of the two adjacent groups, and the most electronegative substituents produce also highest atomic charges at the Ge atom. In addition, replacing F with OH and NH2, the thermochemical stability of the cations substantially increases. This reflects in Lewis acidities of the F2Ge(X)+ and FGe(X)2+ (X=OH, NH2) which are invariably lower than GeF3+. The mechanisms of formation of the FnGe(OH)3-n+ and FnGe(NH2)3-n+ (n=0–2) were also investigated and found to be describable by the initial formation of encounter complexes between the reactant ions GeF3+, F2Ge(X)+ and FGe(X)2+ (X=OH, NH2) and H2O or NH3, which eventually dissociate into FnGe(OH)3-n+ and FnGe(NH2)3-n+ (n=0–2) and HF passing through two consecutive isomerizations.