Ligand-Exchange Equilibrium Measurements in Trapping Devices

3 Ligand-Exchange Equilibrium Measurements in Trapping Devices 

Quadrupole ion trap [111] (QIT) and ion cyclotron resonance (ICR) mass spectrometers [112] have been used for the determination of Gibbs free energies (AG) of ligand exchange (relative basicity), as illustrated by reaction 6.4 for a metal cation M+  

Adducts are trapped in the presence of a known pressure of the ligands and L. When a steady state is observed, usually after a few seconds when working in the 10 -10 Pa range, an equilibrium constant K can be calculated from the pressure ratio of the ligands and the ratio of ion intensities  

When an equilibrium state cannot be achieved, bracketing techniques may be used limits can be placed on the basicity of M+, derived from fast or slow kinetics of cation exchange. In reaction 6.6  

In early studies, alkali metal cations were obtained by thermionic emission, as for HPMS, and later, a large number of metal cations were formed by laser vaporization/ionization of 

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