Control of Fe3+ coordination by excess Cl- in alcohol solutions

Yunika Nomura; Dai Inoue; Yutaka Moritomo

doi:10.1039/d2ra01522f

Control of Fe³⁺ coordination by excess Cl^- in alcohol solutions

RSC Adv. 2022 Jun 17;12(28):17932-17936. doi: 10.1039/d2ra01522f. eCollection 2022 Jun 14.

Authors

Yunika Nomura¹, Dai Inoue², Yutaka Moritomo^{1

2

3

4}

Affiliations

¹ School of Science and Engineering, University of Tsukuba Tsukuba 305-8571 Japan moritomo.yutaka.gf@u.tsukuba.ac.jp.
² Graduate School of Pure and Applied Sciences, University of Tsukuba Tsukuba 305-8571 Japan.
³ Faculty of Pure and Applied Sciences, University of Tsukuba Tsukuba 305-8571 Japan.
⁴ Tsukuba Research Center for Energy Materials Science (TREMS), University of Tsukuba Tsukuba 305-8571 Japan.

Abstract

We spectroscopically investigated coordination state of Fe³⁺ in methanol (MeOH) and ethanol (EtOH) solutions against Cl^- concentration ([Cl^-]). In both the system, we observed characteristic absorption bands due to the FeCl₄ complex at high-[Cl^-] region. In the MeOH system, the proportion (r) of [FeCl₄]^- exhibits a stationary value of 0.2-0.3 in the intermediate region of 10 mM < [Cl^-] < 50 mM, which is interpretted in terms of [FeCl _n L_6-n ]^3-n (n = 1 and 2). In the EtOH system, r steeply increases from 0.1 at [Cl^-] = 1.5 mM to 0.7 at [Cl^-] = 3.5 mM, indicating direct transformation from [FeL₆]³⁺ to [FeCl₄]^-. We further found that the coordination change significantly decreases the redox potential of Fe²⁺/Fe³⁺.