Generalization of the CCS-Mass Equation to Account for Variations in Molecular Density in an Iron-Ligand Complex
Christopher Kune1, Johann Far1, Sophie Rappe1
1Mass Spectrometry Laboratory, MolSys Research Unit, University of Liège, Liège, Belgium.
Rationale:
In this work, the CCS-mass trends equation has been revisited to consider apparent changes in the ion density.
Methods:
The ion mobility-derived collision cross section (IM-derived CCS) of negatively, single-charged Fe(II) and Fe (III) metal centers coordinated with three or four halide or linear alkyl carboxylate ligands generated by electrospray operating in the negative ionization mode were obtained using a T-wave mobility cell.
Results:
The CCS-mass trends were fitted using the equation CCS = A × massPow (where A is an apparent density parameter and Pow is a shape parameter). Iron-halide complexes led to Pow parameters well below the typical limit of 0.5, which could only be explained by refining the fitting equation using a linear combination of these A and Pow parameters. Their physical meaning is described in terms of mass distribution within the volume of the iron-ligand complex ions.
Conclusions:
The analysis of the CCS-mass trend of iron-halide and iron-carboxylate complexes allows us to predict the IM-derived CCS and the CCS-mass trends of combinations of iron-halide/carboxylate complexes. The results show no differences in trend between planar trigonal and tetrahedral geometries as described by the valence shell electron pair repulsion (VSEPR) theory.
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