Gradual solid-state redox-isomerism in the lanthanide series.

Oxidation of [(Ar-bian)Yb(dme)] (1) (Ar-bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene; dme = 1,2-dimethoxyethane) by 0.5 equivalent of MeNC(S)S-S(S)CNMe in dme at ambient temperature affords a mixture of two products, [(Ar-bian)Yb{SC(S)NMe}(dme)] and [(Ar-bian)Yb{SC(S)NMe}(dme)], which represent two redox-isomers (2a and 2b, respectively). Their ratio in solution depends on the solvent as well as on the temperature. In the solid state, a decrease of temperature (350 → 100 K) caused an electron transfer from the Yb ion to the Ar-bian radical-anion in isomer 2b to afford isomer 2a. Accordingly, the ratio of isomers 2a and 2b changes from 1 : 1 (350 K) to 3 : 1 (100 K). In contrast, in the dimer [(dme)(dpp-bian)Yb(μ-Cl)Yb(dpp-bian)(dme)] (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene), which is the sole example of a lanthanide complex that reveals solid-state redox-isomerism (valence tautomerism) reported so far, the electron transfer from the Yb ion to the dpp-bian radical-anion takes place at around 150 K and is completed within a temperature interval of . 7 K.