PNNL

Abstract

Electrospray ionization can generate microsolvated multiply charged metal ions for various metals and ligands, allowing exploration of chemistry within such clusters. The finite size of these systems permits comparing experimental results with accurate calculations, creating a natural laboratory to research ion solvation. Mass spectrometry has provided much insight into the stability and dissociation of ligated metal cations. While solvated singly charged ions tend to shrink by ligand evaporation, solvated polycations below a certain size exhibit charge reduction and/or ligand fragmentation due to organometallic reactions. Here we investigate the acetone complexes of typical divalent metals (Ca, Mn, Fe, Co, Ni, Zn, and Cu), comparing the results of collision-induced dissociation with the predictions from density functional theory. As for other solvated dications, dissociation channels involving proton or electron transfer compete with ligand loss and become dominant for smaller complexes. The heterolytic C-C bond cleavage is common, as one would expect from previous work on DMSO and acetonitrile complexes. Of primary interest is the highly unintuitive neutral ethylene loss, found for all metals studied except Cu and particularly intense for Ca, Mn, and Fe. We focus on understanding that process in the context of competing dissociation channels, as a function of metal identity and number of ligands. According to first-principles modeling, ethylene elimination proceeds along a complex path involving a rearrangement of two acetone ligands and multiple transition states.