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Updated: Sep 6, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Control of Fe3+ coordination by excess Cl- in alcohol solutions
Yunika Nomura1, Dai Inoue2, Yutaka Moritomo1,2,3,4
1School of Science and Engineering, University of Tsukuba Tsukuba 305-8571 Japan moritomo.yutaka.gf@u.tsukuba.ac.jp.
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 L6- ]3- (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+.
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