Solvent displacement in transition metal complexes

Abstract

Ligand exchange reactions of transition metal ions solvated by two acetone or two acetonitrile molecules with multidentate polyethers or pyridyl ligands are undertaken in a quadrupole ion trap mass spectrometer. The ability of the polyether or pyridyl ligand to displace one or both solvent molecules is correlated with the number of binding atoms in the multidentate ligand, the flexibility of the ligand along with its ability to fully coordinate or encapsulate the metal ion, and the strength of the solvent/metal bonds. The smaller polyethers displace one solvent molecule, thus generating stable (M + + polyether + solvent) complexes. The larger polyethers rapidly displace both solvent molecules, leading to formation of stable (M + + polyether) complexes, because of the ability of the large polyethers to encapsulate or fully coordinate the metal ion. The pyridyl ligands tend to favor formation of (M + + pyridyl ligand + solvent) mixed-ligand complexes, regardless of the number of nitrogen atoms or flexibility of the pyridyl ligand. The pyridyl ligands are unable to fully encapsulate the metal ion, so one solvent molecule may remain bound to the metal ion.