Control of Fe 3+ coordination by excess Cl - in alcohol solutions.

We spectroscopically investigated coordination state of Fe 3+ in methanol (MeOH) and ethanol (EtOH) solutions against Cl - concentration ([Cl - ]). In both the system, we observed characteristic absorption bands due to the FeCl 4 complex at high-[Cl - ] region. In the MeOH system, the proportion ( r ) of [FeCl 4 ] - 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 [FeL 6 ] 3+ to [FeCl 4 ] - . We further found that the coordination change significantly decreases the redox potential of Fe 2+ /Fe 3+ .