Reactions of the Metalloid Cluster Anion {Ge-9[Si(SiMe3)(3)](3)}(-) in the Gas Phase. Oxidation- and Reduction-Steps give an Insight onto the Area between Metalloid Clusters and Zintl Ions

The cluster anion {Ge-9[Si(SiMe3)(3)](3)}(-) (1) is transferred intact into the gas phase via the electro spray method. Subsequently the fragmentation of I alter resonant excitation as well as the oxidation reaction with O-2 and Cl-2 are investigated in an FT-ICR mass spectrometer (Fourier Transform Ion Cyclotron Resonance). Unlike former results with off-resonant excitation the fragmentation leads mainly to the end-product Ge-9(-). Moreover, applying an on-resonant excitation the dissociation experiment can be quantified; 2.0 +/- 0.15 eV (193 +/- 15 kJ.mol(-1)) for the elimination of the first two ligands and 2.7 +/- 0.15 eV (261 +/- 15 kJ.mol(-1)) for all ligands, respectively. Particular attention is turned on the first step, where sterically encumbered Si-2(SiMe3)(6) molecules are formed in a concerted reaction. This result, which is also important for elemental reactions on metal surfaces in catalyses, is based on experimentally determined threshold energies, DFT calculations and calculations on the lifetime of the involved species. In contrast to the high reactivity of crystalline 1 center dot Li(THF)(4), gaseous 1 is inert against oxygen. The analogy to recently published spin forbidden reactions of Al-13(-) with O-2 hints to a general importance of spin conversion during gas phase reactions of larger cluster molecules. The oxidation of I with Cl-2 proceeds through different reaction channels. DFT calculations give a first insight on the complex primary oxidation steps. These calculations also reveal that the delocalized bonding situation in the Ge-9 core is distorted upon oxidation. This result together with the dissociation experiments shed more light on differences and similarities between metalloid clusters and Zintl ions.