Coordination Structure and Fragmentation Chemistry of the Tripositive Lanthanide-Thio-Diglycolamide Complexes

Tripositive Ln(TMTDA)₃³⁺ complexes (Ln = La-Lu except Pm, TMTDA = tetramethyl 3-thio-diglycolamide) were observed in the gas phase by electrospray ionization of LnCl₃ and TMTDA mixtures. Collision-induced dissociation (CID) was employed to investigate their fragmentation chemistry, which revealed the influence of metal center as well as ligand on the ligated complexes. Ln(TMTDA)₂(TMTDA-45)³⁺ resulting from C_carbonyl-N bond cleavage of TMTDA and hydrogen transfer was the major CID product for all Ln(TMTDA)₃³⁺ except Eu(TMTDA)₃³⁺, which predominantly formed charge-reducing product Eu^II(TMTDA)₂²⁺ via electron transfer from TMTDA to Eu³⁺. Density functional theory calculations on the structure of La(TMTDA)₃³⁺ and Lu(TMTDA)₃³⁺ revealed that Ln³⁺ was coordinated by six O_carbonyl atoms from three neutral TMTDA ligands, and both complexes possessed C_3h symmetry. The S_ether atom deviating from the ligand plane was not coordinated to the metal center. On the basis of the CID results of Ln(TMTDA)₃³⁺, Ln(TMGA)₃³⁺, and Ln(TMOGA)₃³⁺, the fragmentation chemistry associated with the ligand depends on the coordination mode, while the redox chemistry of these tripositive ions is related to the nature of both metal centers and diamide ligands.