Use of IMMS for the investigation of the effects of shapes, densities and dipole moments on the CCS of small metal complexes

Ion mobility mass spectrometry provides the collision cross section (CCS) of ions in the gas phase. The CCS growth of ions sharing similar physicochemical properties such as charge state, geometry, shape, apparent density and dipole moments correlates well with their masses evolution. In this presentation, we study the effect on the CCS/mass correlations after variation of these physicochemical properties using a set of negatively charged iron center complexes with halogens (chloride, bromide and iodide) and carboxylates (linear or branched mono carboxylate) as ligands. Due to the halogen ligands are more compact and denser than the carboxylate ligands, all combinations of these ligands lead to a set of iron center complexes (theoretically superior to 250 complexes) having different CCS growth. Indeed, the number of ligands imposes the geometry (linear, trigonal plan, tetrahedral) while the halogen/carboxylate ligands ratio influences the apparent densities and the shape (spherical or near spherical) of the complex ions. Moreover, theses complex ions also share different dipole moment. These properties have been estimated by computational chemistry (Molecular Mechanism or Density Functional Theory levels) for each complex whereas the CCS and mass values have been measured by traveling wave ion mobility (Water’s Synapt G2). Comparing all the experimental CCS/mass trends in function of the physicochemical properties shows that the apparent density is the main factor influencing these correlations following by the shape and geometry factors. The variations on the dipole moment of theses complexes seems to be insufficient to significantly affect the CCS/mass correlation. This work also highlights the capability of CCS prediction of a given ion based on its mass, apparent density, shape, geometry, and the dipole moment.