Collisionally activated dissociation of transition metal ion/polyether complexes in a quadrupole ion trap

For a series of polyether/transition metal ion complexes, collisionally activated dissociation reactions that are mediated by the flexibility of the polyether and the number of coordination sites are reported. The metal ions are generated by a pulsed laser desorption technique, and collision-activated dissociation methods are used to characterize the structures of the resulting metal/polyether complexes. The CAD patterns for the different polyether/metal ion complexes show striking variations depending on the flexibility of the ether, its number of coordination sites, and the type of metal ion. For example, (18-crown-6 + Co+) dissociates by loss of CH=CH. or C2H3O. radicals, each pathway in conjunction with multiple losses of C2H4O, and resulting in products incorporating one covalent or ionic bond between the Co+ ion and the crown ether. In contrast, (12-crown-4 + Co+) dissociates by loss of CH2=CH2 or C2H4O closed shell neutrals, each pathway in conjunction with additional losses of C2H4O and resulting in products that incorporate no covalent bonds to Co+. The polyether/Ni+ complexes show dissociation behavior that is similar to that observed for the Co+ complexes, but the polyether/Cu+ complexes show uniform dissociation trends that seem to be independent of the flexibility and number of coordination sites of the ether. These differences are rationalized based on the nature of the metal ion, and both the flexibility of the crown ether and its number of coordinating sites, factors which affect the geometry during coordination of the metal ion. This idea is supported by comparative dissociation reactions of metal complexes containing acyclic polyethers (glymes) which have more flexible structures. MS/MS/MS experiments and CAD of complexes formed by model compounds offer support for the dissociation mechanisms.