Evidence of Sharp Transitions between Octahedral and Capped Trigonal Prism States of the Solvation Shell of the Aqueous Fe 3+ Ion

• Published in: The journal of physical chemistry letters Vol. 15; no. 17; pp. 4523 - 4530
• Main Authors: Goswami, Amrita, Peña-Torres, Alejandro, Jónsson, Elvar Ö, Egorov, Sergei A, Jónsson, Hannes
• Format: Journal Article
• Language: English
• Published: United States 02-05-2024
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.4c00756

The structure of the solvation shell of the aqueous Fe
ion has been a subject of controversy due to discrepancies between experiments and different levels of theory. We address this issue by performing simulations for a wide range of ion concentrations, using various potential energy functions, supplemented by density functional theory calculations of selected configurations. The solvation shell undergoes abrupt transitions between two states: a hexacoordinated octahedral (OH) state and a capped trigonal prism (CTP) state with 7-fold coordination. The lifetime of these states is dependent on concentration. In dilute FeCl
solutions, the lifetimes of both are similar (≈1 ns). However, the lifetime of the OH state increases with ion concentration, while that of the CTP state decreases slightly. When a uniform negative background charge is used instead of explicit counterions, the lifetime of the OH state is greatly overestimated. These findings underscore the need for further experimental measurements and higher-level simulations.