Generalization of the CCS-Mass Equation to Account for Variations in Molecular Density in an Iron-Ligand Complex Growing System.

Abstract

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 × mass^Pow (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.