Interactions between the trianionic ligand-centred redox-active metalloligand [Cr(III)(perfluorocatecholato)3](3-) and guest metal ions.

Abstract

The redox-active metalloligand (RML) (Et3NH)3[Cr(III)(F4Cat)3] (F4Cat = perfluorocatecholato) () was synthesized and its interactions with guest metal ions Li(+), Mn(2+), Fe(2+), Co(2+), Cu(2+), and Zn(2+) were examined. Cyclic voltammetry measurements and spectroelectrochemical studies revealed that complex shows three-step ligand-centred one-electron oxidation to consecutively generate [Cr(III)(F4Cat)2(F4SQ)](2-) (F4SQ = perfluorosemiquinonato), [Cr(III)(F4Cat)(F4SQ)2](-), and [Cr(III)(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. Titration experiments in MeCN revealed that treatment of with Cu(2+) leads to the formation of [Cr(III)(F4Cat)2(F4SQ)](2-) and Cu(+)via a redox reaction. However, when was treated with Li(+), Mn(2+), Fe(2+), Co(2+), and Zn(2+), further titration experiments revealed that these metal ions coordinated via the lone pairs on the coordinating oxygen atoms of the F4Cat(2-) moieties in a one-to-one ratio, and binding constants of 3.7 (±0.3) × 10(4) (Li(+)), 1.5 (±0.2) × 10(5) (Mn(2+)), 2.2 (±0.4) × 10(5) (Fe(2+)), 1.9 (±0.2) × 10(5) (Co(2+)), and 3.8 (±0.4) × 10(5) M(-1) (Zn(2+)) were established. Moreover, the oxidation potentials of were positively shifted by 0.08-0.33 V upon addition of guest metal ions. Spectroelectrochemical studies of in the presence of guest metal ions suggested that ligand-centred one- and two-electron oxidation of the RML occurred for Li(+), Mn(2+), Co(2+), and Zn(2+), respectively, while guest metal-centred one-electron oxidation was observed for Fe(2+). Considering all the aforementioned results, this study demonstrated for the first time the ability of [Cr(III)(F4Cat)3](3-) to act as a RML in solution.