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

Electrospray ionization (ESI) of LnCl₃ (Ln = La-Lu except Pm) and TMGA (tetramethyl glutaramide) mixtures resulted in the formation of gas-phase Ln(TMGA)₃³⁺ 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)₃³⁺ except Eu(TMGA)₃³⁺ which predominantly forms divalent Eu^II(TMGA)₂²⁺ complex via loss of TMGA⁺. Analogous Yb^II(TMGA)₂²⁺ and Sm^II(TMGA)₂²⁺ 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)₃³⁺, tripositive ions such as Ln(TMGA)₄³⁺ and Ln(TMGA)₂³⁺ were experimentally identified as well. While the former was observed along with Ln(TMGA)₃³⁺ during ESI, the latter was observed upon CID of Ln(TMGA)₃³⁺, suggesting two TMGA molecules can stabilize Ln³⁺ in the gas phase. Graphical Abstract ᅟ.