Lawrence Berkeley National Laboratory

Gas-phase lanthanide-SO2 complexes, Ln(CH3SO2)3(SO2)-, were produced by collision induced dissociation (CID) of Ln(CH3SO2)4- precursors prepared by electrospray ionization. For all lanthanides except Eu, CID of Ln(CH3SO2)4- resulted in CH3 loss to form Ln(CH3SO2)3(SO2)-, which spontaneously react with O2 to form Ln(CH3SO2)3(O2)-. CID of Eu(CH3SO2)4- produced only Eu(CH3SO2)3-, with reduction from Eu(III) to Eu(II). For Ln = Yb and Sm, the Ln(CH3SO2)4- underwent neutral ligand loss to form Ln(CH3SO2)3-, which reacted with O2 to yield Ln(CH3SO2)3(O2)-, recovering the Ln(III) oxidation state. The CID results show parallels to condensed-phase Ln3+/Ln2+ redox chemistry. Density functional theory (DFT) calculations on Ln(CH3SO2)3(SO2)- for Ln = La, Yb and Lu reveal that SO2 acts as a bidentate oxygen bound ligand for doublet ground-state La(CH3SO2)3(SO2)- and Lu(CH3SO2)3(SO2)-, while the ground state for Yb(CH3SO2)3(SO2)- is an open-shell singlet with a monodentate SO2 ligand. Loss of CH3 is computed to be much more favorable than neutral ligand loss for La(CH3SO2)4- and Lu(CH3SO2)4-, whereas both channels are comparable in energy for Yb(CH3SO2)4-, in accord with the experiments. DFT results for fragmentation of Cu(CH3SO2)2- reveal that formation of the organometallic complex, Cu(CH3SO2)(CH3)-, is energetically most favorable, in agreement with contrasting fragmentation pathways of copper and lanthanide complexes.