Evaluating electrochemical accessibility of 4fn5d1 and 4fn+1 Ln(ii) ions in (C5H4SiMe3)3Ln and (C5Me4H)3Ln complexes

Abstract

The reduction potentials (reported vs. Fc⁺/Fc) for a series of Cp′₃Ln complexes (Cp′ = C₅H₄SiMe₃, Ln = lanthanide) were determined via electrochemistry in THF with [ⁿBu₄N][BPh₄] as the supporting electrolyte. The Ln(III)/Ln(II) reduction potentials for Ln = Eu, Yb, Sm, and Tm (−1.07 to −2.83 V) follow the expected trend for stability of 4f⁷, 4f¹⁴, 4f⁶, and 4f¹³ Ln(II) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4fⁿ5d¹ Ln(II) ions (n = 2–14), fall in a narrow range of −2.95 V to −3.14 V. Only cathodic events were observed for La and Ce at −3.36 V and −3.43 V, respectively. The reduction potentials of the Ln(II) compounds [K(2.2.2-cryptand)][Cp′₃Ln] (Ln = Pr, Sm, Eu) match those of the Cp′₃Ln complexes. The reduction potentials of nine (C₅Me₄H)₃Ln complexes were also studied and found to be 0.05–0.24 V more negative than those of the Cp′₃Ln compounds.