Lanthanide–sulfur gas-phase chemistry: reactions of Ln+ with S8
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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 [LnSx]+ ions is described. Each lanthanide generates sequences of products [LnSx]+ 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+ (f7s1) 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 [LnSx]+ probably contain co-ordinated S2, S3 and S4, while some of the larger [LnSx]+ 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.