ELECTROSPRAY MASS-SPECTROMETRIC STUDY OF [M3O(RCOO)6L3]+ CATIONS (M = CR, FE L = H2O, MEOH, PY)

Electrospray mass spectrometric (ESMS) studies have been made on some representative examples of the trinuclear complexes [M3O(RCOO)6(H2O)3]+ (M = Cr, Fe; R = H, CH3, CH3CH2, (CH3)3C) in methanol and pyridine/methanol solutions. The nonbridging water ligands in the Cr(III) complexes partially exchange with the solvent molecules and ions containing the central Cr3O(RCOO)6 core, and various combinations of terminal ligand are observed. At low first skimmer voltages, intact ions with three terminal ligands are detected, but as the skimmer voltage is increased, interaction with solvent molecules within the ion source causes collisionally activated decompositions to occur, leading to progressive loss of the labile terminal groups. The ES mass spectra of [Fe3O(CH3COO)6-(H2O)3]+ in MeOH or pyridine/MeOH show that the water molecules exchange completely with the solvent, and for other iron derivatives the core carboxylate ligands exchange completely with the acetate in the mobile phase used in the spectrometer. Collisionally activated decomposition (CAD) mass spectra (argon, 200 V) have been observed for some of the core ions [M3O(CH3COO)6]+.