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/m ethanol solutions. The nonbridging water ligands in the Cr(III) comple xes partially exchange with the solvent molecules and ions containing the central Cr3O(RCOO)6 core, and various combinations of terminal lig and are observed. At low first skimmer voltages, intact ions with thre e terminal ligands are detected, but as the skimmer voltage is increas ed, interaction with solvent molecules within the ion source causes co llisionally activated decompositions to occur, leading to progressive loss of the labile terminal groups. The ES mass spectra of [Fe3O(CH3CO O)6-(H2O)3]+ in MeOH or pyridine/MeOH show that the water molecules ex change 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 decompo sition (CAD) mass spectra (argon, 200 V) have been observed for some o f the core ions [M3O(CH3COO)6]+.