Electrospray mass spectrometry of inert and labile metal alkyl compounds: a study of methyl and dimethyl derivatives of gold(III), indium(III) and thallium(III)

Abstract

Electrospray mass spectra have been obtained from methanol solution for a number of cationic methyl and dimethyl derivatives of gold(III), indium(III) and thallium(III), the other ligands being usually polydentate nitrogen bases. The gold compounds were all non-labile dimethyl derivatives and they invariably gave the principal ion in the ES mass spectrum, but loss of both methyl groups could be achieved by collisional activation within the ion source, especially at higher ion source energies. Collisionally activated decomposition (CAD) mass spectra were also investigated by tandem mass spectrometry using argon, and the mode of further fragmentation depended upon the nature of the polydentate nitrogen ligand. Some of the indium(III) complexes also gave the principal ion, but for those cations containing a coordinated water molecule in the solid state the ion of highest m/z observed was the daughter ion corresponding to loss of water from the principal ion. The ES mass spectra of dimeric species of the type [(MeIn) 2L 2(NO 3)(H 2O)] + (L is a polydentate bridging alkoxide ligand), which are known to be labile in solution, give [(MeIn) 2L 2] 2+ as the base peak, but they do also show ions corresponding to [(MeIn) 2L 2(NO 3)] + or [(MeIn) 2L 2(OAc)] +, the acetate originating from the mobile phase used in the spectrometer. In the solid state, the thallium complexes all contain either coordinated water ligands or bridging nitrato groups and some of them are not ionic in the solid state. The cationic thallium compounds do not show the principal ions in their ES mass spectra, but rather the daughter ions expected by loss of water. The neutral solid state polymeric species gives ions in their ES mass spectra corresponding to loss of the nitrato groups in solution, but the weakly coordinated nitrogen bases are retained in the ES mass spectra.