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The development of stable, Earth-abundant, and high-activity molecular water oxidation catalysts under acidic and neutral conditions remains a great challenge. Here, the use of N-heterocyclic carbene (NHC)-based iron(III) complex 1 {[phenyl(tris(3-methylimidazol-1-ylidene))borate]2Fe(III)}+ as a catalyst for water oxidation under acidic and neutral conditions was investigated. Two iron(II) carbene complexes, 2 {[2,6-bis(3-methylimidazolium-1-yl)pyridine]2Fe}2+ and 3 {[2,6-bis(3-methylimidazolium-1-yl)pyridine-4-carboxylic acid]2Fe}2+, were also used for comparison. A series of experiments demonstrate that complex 1 has excellent performance in terms of both catalytic activity and stability. In addition, the faradaic efficiency and turnover frequency (TOF) reach 95.0% and 2.8 s−1, respectively. An overpotential of ca. 490 mV is obtained at pH 1.5. Density functional theory (DFT) calculations indicate that dehydrogenation is the potential-determining step (PDS) in water oxidation. Complex 1 has a lower free energy barrier in this process than 2 and 3. High-valent Fe species are further proven in 1 by spectroelectrochemical measurements, which are crucial in promoting water oxidation. This study is expected to contribute to the development of homogeneous water oxidation catalysis under acidic and neutral conditions. [ABSTRACT FROM AUTHOR]

A novel turn-on fluorogenic aldehyde-appended salamo-like copper(II) complex probe (ASC) was rationally designed and exploited for the two-pronged sensing of thiosulfate (S2O32−) ions and glutathione (GSH) based on an intramolecular charge transfer (ICT) process, which could be fully characterized by using various spectroscopic techniques. It is worth noting that the solid-state crystal structure of the Cu(II) complex is rarely different from its structure in solution (ASC) through a single-crystal X-ray diffraction experiment. Importantly, the developed probe exhibited good sensitivity in response to S2O32− and GSH in an aqueous DMF medium within a detection limit of 149 and 131 nM, respectively. Meanwhile, the designed complex probe could be capable of discriminatively detecting S2O32− ions over other sulfur-containing anions. The probe ASC was applied in real water samples utilizing tap water and rain water for the detection of the S2O32− ion. In addition, this probe could be successfully applied to test strips towards S2O32− and GSH. Finally, we unveiled the rationality of the fluorescence "off–on" responses of ASC to S2O32− and GSH by means of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations. [ABSTRACT FROM AUTHOR]