Self-Assembly of Quaterpyridine Ligands and Cu+ Cations into Helical Complexes of 2:2 Stoichiometry under Electrospray Ionisation Conditions

Abstract

Solutions containing the quaterpyridine ligand 1 and Cu2+ cation were analysed by electrospray ionisation mass spectrometry (ESI-MS). It was found that copper reduction under ESI conditions and self-assembly of 1 and Cu(I) led to the formation of the 2:2 stoichiometry complex. Such stoichiometry is characteristic of the helical complex of a quaterpyridine ligand with Cu(I). The isotope pattern characteristic of the [Cu212]2+ ion, which is different from that of [Cu1]+ ion, is observed. When using methanol as the solvent, only [Cu212]2+ ions are observed in the mass spectrum obtained at low cone voltage. At higher cone voltage, the [Cu212]2+ ion easily dissociates, producing a [Cu1]+ ion. When using other solvents studied, water and acetonitrile, the 2:2 stoichiometry complex is formed, but along with complexes of other stoichiometries. The helical complex was not observed for the silver cation for which only a 1:1 stoichiometry complex was observed (ion [Ag1]+).