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Phys Chem Chem Phys. 2005 Apr 21;7(8):1687-93.

Monitoring reagent modification of charged SnxOy nanoclusters using Fourier transform ion cyclotron mass spectrometry.

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Isotope and Mass Spectrometry Labs, Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia.


The ion-molecule reactions of laser-generated radical clusters SnxO(x+1)(-) (x = 1-6), SnxO(x-1)(+) (x = 1-6) and SnxOx(+) (x = 2, 3) with the reagents H2S and CH3OH have been investigated using FTICR-MS. For the hypermetallic cations SnxO(x-1)(+), the rates of the sulfur-for-oxygen substitution reactions with H2S appear to be sensitive to LDA/DFT-predicted oxygen binding modes, with mu3-O modes relatively inert with respect to mu-O conformations. The reactions of the hypometallic anions SnxO(x+1)(-) with H2S were dominated by proton transfer, although S-for-O substitution was observed to be kinetically competitive. The rates of the proton transfer were found to vary with both the reagent and cluster anion, and an analysis of the reaction kinetics for SnxO(x+1)(-) afforded the relative cluster proton affinities: PA(Sn2O3-) > PA(SnO2-) >> PA(Sn3O4-) > PA(Sn5O6-) approximately PA(Sn6O7-) approximately PA(CH3O-) = 381 +/- 2 kcal mol(-1) > PA(Sn-) = 352 +/- 10 kcal mol(-1). Ion-molecule reaction results for the hypermetallic cations x = 2-5 with CH3OH are suggestive of gas-phase coordination chemistry, with each cluster undergoing one slow association reaction. A recurrent theme of the chemistry of ionic SnxOy is the initial activation or generation of OySnx(-/+)-OH bonds by a radical mechanism involving hydrogen or hydroxyl abstraction from the reagent. The resulting cluster-hydroxyl bonds are relatively labile with respect to conversion to alkoxy ligands.

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