Lanthanide–sulfur gas-phase chemistry: reactions of Ln⁺ with S₈ †

Abstract

All of the lanthanides except promethium have been treated as monocations Ln⁺ with S₈(g), in an ion cyclotron resonance mass spectrometer. A rich array of 213 new [LnS_x]⁺ ions is described. Each lanthanide generates sequences of products [LnS_x]⁺ in which x generally increases with time. Dominant intermediate ions in these sequences occur with x = 2 (La, Gd), 3 (Eu, Yb), 4 (Nd, Sm, Tb, Dy, Ho, Er, Tm, Lu), 6 (La, Ce, Pr), 9 (Yb), 10 (Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), 11 (Eu), 12 (La, Ce, Pr, Gd), 14 (La) and 18 (Nd). The largest product observed is [LnS₂₁]⁺ for La and Pr, and the size of the largest ion drops towards the end of the lanthanide series. There is a remarkable similarity between the reactions of Eu⁺ (f ⁷s¹) and Ca⁺ (s¹) with S₈: both form [MS₃]⁺ rapidly, then add S₈ rapidly to form an isomer which can easily dissociate S₈, and also form more slowly a second isomer [MS₁₁]⁺ which is more stable. Other M⁺ with s¹ ground-state configurations do not behave similarly. The smaller [LnS_x]⁺ probably contain co-ordinated S₂, S₃ and S₄, while some of the larger [LnS_x]⁺ may contain associated S₈ molecules not bonded directly to Ln. Reaction rates correlate approximately with the occurrence of a ground or low excited state with two unpaired non-f electrons.

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