Fragmentation Pathways of [Mg(NH3) n ]2+ Complexes:  Electron Capture versus Charge Separation

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 110; no. 27; pp. 8423 - 8432
• Main Authors: Wu, Bohan, Duncombe, Bridgette J, Stace, Anthony J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.07.2006
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp0573442

New experimental results are presented from a detailed study of gas-phase [Mg(NH3) n ]2+ complexes and their fragmentation pathways. The reactions examined range from those observed as metastable (unimolecular) decompositions through to collision-induced processes, which have been accessed using a variety of collision gases. Measurements of ion intensity distributions coupled with unimolecular decay studies show that [Mg(NH3)4]2+ not only is the most intense species detected but also sits at a critical boundary between complexes that are unstable with respect to charge separation and those that are sufficiently solvated to be deemed stable on the time scale of the experiment. Metastable fragmentation patterns have been used to provide information on the evolution of solvent structure around the central dication. In addition to highlighting the particular significance of [Mg(NH3)4]2+, these measurements show some evidence to suggest the buildup of structures via a hydrogen-bonded network to give conformers of the form (4+1) and (4+2), respectively. Collision-induced dissociation studies show the ions to exhibit several fragmentation pathways, including the loss of NH3 and NH3 + H, which are promoted primarily through electron capture dissociation (ECD). This picture contrasts with the conclusion from a number of earlier studies that collisional activation mainly promotes charge separation. From the results presented it is suggested that electron capture may play a more dominant role in the charge reduction of multiply charged metal−ligand species than had previously been appreciated.