Journal Article Interactions between the trianionic ligand-centred redox-active metalloligand [CrIII(perfuorocatecholato)3]3− and guest metal ions

脇坂, 聖憲  ,  Wakizaka, Masanori

The redox-active metalloligand (RML) (Et3NH)3[CrIII(F4Cat)3] (F4Cat = per!uorocatecholato) (1) was synthesizedand its interactions with guest metal ions Li+, Mn2+, Fe2+, Co2+, Cu2+, and Zn2+ were examined.Cyclic voltammetry measurements and spectroelectrochemical studies revealed that complex 1 showsthree-step ligand-centred one-electron oxidation to consecutively generate [CrIII(F4Cat)2(F4SQ)]2−(F4SQ = per!uorosemiquinonato), [CrIII(F4Cat)(F4SQ)2]−, and [CrIII(F4SQ)3] at −0.12, 0.23, and 0.53 V vs.Ag/Ag+ in dichloromethane, or at −0.21, 0.08, and 0.50 V in acetonitrile (MeCN), respectively. Titrationexperiments in MeCN revealed that treatment of 1 with Cu2+ leads to the formation of[CrIII(F4Cat)2(F4SQ)]2− and Cu+ via a redox reaction. However, when 1 was treated with Li+, Mn2+, Fe2+,Co2+, and Zn2+, further titration experiments revealed that these metal ions coordinated via the lone pairson the coordinating oxygen atoms of the F4Cat2− moieties in a one-to-one ratio, and binding constantsof 3.7 (±0.3) × 104 (Li+), 1.5 (±0.2) × 105 (Mn2+), 2.2 (±0.4) × 105 (Fe2+), 1.9 (±0.2) × 105 (Co2+), and3.8 (±0.4) × 105 M−1 (Zn2+) were established. Moreover, the oxidation potentials of 1 were positivelyshifted by 0.08–0.33 V upon addition of guest metal ions. Spectroelectrochemical studies of 1 in thepresence of guest metal ions suggested that ligand-centred one- and two-electron oxidation of the RMLoccurred for Li+, Mn2+, Co2+, and Zn2+, respectively, while guest metal-centred one-electron oxidationwas observed for Fe2+. Considering all the aforementioned results, this study demonstrated for the "rsttime the ability of [CrIII(F4Cat)3]3− to act as a RML in solution.

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