Electrospray production and collisional dissociation of lanthanide/methylsulfonyl anion complexes: Sulfur dioxide anion as a ligand

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 O-2 to form Ln(CH3SO2)(3)(O-2)(-). 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 O-2 to yield Ln(CH3SO2)(3)(O-2)(-), recovering the Ln(III) oxidation state. The CID results show parallels to condensed-phase Ln(3+)/Ln(2+) 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. (C) 2015 Elsevier B.V. All rights reserved.