Study of formation and fragmentation of ionic complexes of polydentate ligands with Al(III) and glycerol by fast atom bombardment mass spectrometry. Part 1: Polydentate ligands

Abstract

The complexation reactions of aluminum ions with polydentate ligands such as 12-crown-4,15-crown-5,18-crown-6, 1,10-dithia-18-crown-6, dicyclohexyl-18-crown-6, dibenzo-18-crown-6, and dibenzo-24-crown-8 and acyclic analogs mono-, di-, tri-, tetra-, penta-, and hexaethylene glycols were studied using FAB mass spectrometry. These cyclic ligands form (M + 117)+, (M + 157)+, (M + 231)+, and (M + 253)+ ions with different aluminum-containing species. Collisionally activated dissociations of these adduct ions gave fragment ions, initially due to the loss of ligands directly attached to aluminum, followed by insertion of aluminum into the remaining ligand skeleton. Further fragmentation of the metal-containing species gave ions corresponding to consecutive losses of C2H4O units. Fragmentations of deuterium-labelled ions were used to help in establishing fragmentation pathways. Selectivity towards metal chelation is observed in this order: 12-crown-4 < 15-crown-5 < 18-crown-6. The elemental compositions of adduct ions were confirmed by high-resolution measurements. The formation of (M + Al − 2H)+ ion, obtained by the displacement of two hydroxy protons, is more favored for tetra- and pentaethylene glycols. Key words: crown ethers, polyethylene glycols, aluminum(III)–glycerol, ionic complexes and ion dissociations.