Formation and Fragmentation Chemistry of Tripositive Ln(TMGA)33+ Complexes in the Gas Phase

Electrospray ionization (ESI) of LnCl(3) (Ln = La-Lu except Pm) and TMGA (tetramethyl glutaramide) mixtures resulted in the formation of gas-phase Ln(TMGA)(3)(3+) complexes, where tripositive lanthanide cation was coordinated by three neutral TMGA ligands. Collision induced dissociation (CID) was employed to investigate the fragmentation chemistry of these tripositive complexes. Ln(TMGA)(2)(TMGA- 45)(3+) resulting from C-carbonyl-N bond cleavage of TMGA and hydrogen transfer is the major CID product for all Ln(TMGA)(3)(3+) except Eu(TMGA)(3)(3+) which predominantly forms divalent Eu-II(TMGA)(2)(2+) complex via loss of TMGA(+). Analogous Yb-II(TMGA)(2)(2+) and Sm-II(TMGA)(2)(2+) complexes arising from charge reduction were also observed, in competition with the formation of charge conserving Yb-III(TMGA)(TMGA-H)(2+) and Sm-III(TMGA)(TMGA-H)(2+) products. The yield of these charge reducing products follows their reduction potentials in condensed phase. In addition to Ln(TMGA)(3)(3+), tripositive ions such as Ln(TMGA)(4)(3+) and Ln(TMGA)(2)(3+) were experimentally identified as well. While the former was observed along with Ln(TMGA)(3)(3+) during ESI, the latter was observed upon CID of Ln(TMGA)(3)(3+), suggesting two TMGA molecules can stabilize Ln(3+) in the gas phase.