Gas-phase reactions of doubly charged alkaline earth and transition metal complexes of acetonitrile, pyridine, and methanol generated by electrospray ionization

Formation and low energy collision-induced dissociation (CID) of doubly charged metal(II) complexes (metal(II)+L _n ]²⁺, metal(II)=Co(II), Mn(II), Ca(II), Sr(II) and L = acetonitrile, pyridine, and methanol) were investigated. Complexes of metal(II)+L _n ]²⁺ where n≤7 were obtained using electrospray ionization. Experimental parameters controlling the dissociation pathways for Co(II)+(CH₃CN)₂]²⁺ were studied and a strong dependence of these processes on the collision energy was found. However, the dissociation pathways appear to be independent of the cone potential, indicating low internal energy of the precursor ions. In order to probe how these processes are related to intrinsic parameters of the ligand such as ionization potential and metal ion coordination, low energy CID spectra of metal(II)+L _n ]²⁺ for ligands such as acetonitrile, pyridine, and methanol were compared. For L = pyridine, all metals including the alkaline earth metals Ca and Sr were reduced to the bare metal(I)]⁺ species. Hydride transfer was detected upon low energy CID of metal(II)+L _n ]²⁺ for metal(II)=Co(II) and Mn(II) and L = methanol, and corroborated by signals for metal(II)+H^?]⁺ and metal(II)+H^?+CH₃OH]⁺, as well as by the complementary ion CH₃O]⁺.