Acetonitrile complexes of triply charged metal ions: are ligated trications intrinsically more prone to charge reduction than dications?

The development of electrospray has enabled the generation of gas-phase solvated multiply charged metal ions. Complexes involving both protic ligands (water, alcohols) and aprotic ones (e.g., ketones, DMSO, acetonitrile) were found for dications, but trications were compatible with aprotic ligands only. Here, to probe this difference in stability, acetonitrile complexes of metal trications were formed by ESI and collisionally fragmented. Proton transfer, electron transfer, and heterolytic cleavage channels previously found for dications were observed. Characteristic sizes for these processes suggest an intrinsic gap in the stability of dication and trication complexes against proton transfer, but not against electron transfer.