Electrochemical investigation of the kinetics of chloride substitution upon reduction of [Ru(porphyrin)(NO)Cl] complexes in THF.

The electrochemistry of several ruthenium porphyrin nitrosyl chloride complexes [Ru(por)(NO)Cl] have been examined in tetrahydrofuran. The complexes undergo 1-electron irreversible reductions which result in the diffusion-limited substitutions of the chloride ligands for THF. This chloride metathesis is reversible in the presence of added NBu4Cl, and equilibrium constants and rate constants for chloride loss have been estimated. These parameters correlate with the NO stretching frequencies of the parent complexes, with more electron-donating porphyrin ligands favouring chloride loss from the reduced complexes. The [Ru(por)(NO)(THF)] products of the reductions can be detected by IR, EPR and visible spectroscopies. These species undergo three further reductions, with good reversibility at scan rates \u3e0.40 V s-1. The [Ru(por)(NO)(THF)]+/0 couples have also been determined, and the rate constants and equilibrium constants for recombination with chloride have been estimated. One-electron reductions of the [Ru(por)(NO)Cl] complexes result in ~1018 enhancement of the rates of chloride loss

Bis(cobaltocenium) tetrachloridocobaltate(II) dichloromethane 1.2-solvate

The structure of bis(cobaltocenium) tetrachloridocobaltate(II) dichloromethane 1.2-solvate, [Co(C5H5)2]2[CoCl4]·1.2CH2Cl2, has been determined at 100 K. The title compound crystallizes in the space group P\overline{1} and is an example of an unusual Z′ = 5 structure. The asymmetric unit contains ten cobaltocenium ions, five tetrachloridocobaltate(II) ions and six molecules of dichloromethane, i.e. 5{[Cp2Co]2[CoCl4]}·6CH2Cl2. All the cobaltocenium ions are determined to be in the eclipsed conformation with respect to the cyclopentadienyl rings

Bis(cobaltocenium) tetrachloridocobaltate(II) dichloromethane 1.2-solvate

The structure of bis(cobaltocenium) tetrachloridocobaltate(II) dichloromethane 1.2-solvate, [Co(C5H5)2]2[CoCl4]1.2CH2Cl2, has been determined at 100 K. The title compound crystallizes in the space group P1 and is an example of an unusual Z0 = 5 structure. The asymmetric unit contains ten cobaltocenium ions, five tetrachloridocobaltate(II) ions and six molecules of dichloromethane, i.e. 5{[Cp2Co]2[CoCl4]}6CH2Cl2. All the cobaltocenium ions are determined to be in the eclipsed conformation with respect to the cyclopentadienyl rings

Protonation of Pendant Pyridine Substituents in an Iron Porphyrin Hangman Complex: Influence on Spectral Visibility and Electrocatalysis

A hangman complex based on a functionalized iron porphyrin with two covalently attached pyridine (hanging) groups (Py2XPFe) was immobilized onto rough silver electrodes. To elucidate the protonation state of the hanging groups, surface-enhanced resonance Raman (SERR) spectroscopy was performed for the complete complex and a truncated molecular version without the porphyrin unit (Py2XBr) in buffers of different pH values (6.0–8.5). Spectra simulations of Py2XBr for different protonation states suggested three different interaction modes: one in which one proton is shared between both functional groups in a Zundel-like way, another one is a proton located at only one of the pyridine substituents, and a third one in which both pyridines are protonated. Comparison with experimental Raman difference spectra indicated that shared protonation predominates in the pH range of 8.0 to 7.5 and the double protonation in more acidic buffers. The local protonation appears as a potential-dependent intermediate at neutral pH. These results were correlated with the spectral data of the hangman complex Py2XPFe as a function of electric potential, demonstrating that only for a single localized protonation state the SERR spectra of the reduced FeII-porphyrin were visible. Using the electrocatalytic oxygen reduction reaction (ORR) as a model reaction, it was furthermore shown that the pH- and potential-dependent protonation of the pyridine groups has an influence on the reaction pathway

Covalent Trapping of Cyclic-Polysulfides in Perfluorinated Vinylene-Linked Frameworks for Designing Lithium-Organosulfide Batteries

The strategic combination of redox-active triazine- or quinoxaline-based lithium-ion battery (LIB) mechanisms with the polysulfide ring-mediated lithium-sulfur battery (Li-SB) mechanism enabled the configuration of covalent organic-framework (COF)-derived lithium-organosulfide (Li-OrSB) battery systems. Two vinylene-linked frameworks were designed by enclosing polysulfide rings via postsynthetic framework sulfurization, allowing for the separate construction of triazine-polysulfide and quinoxaline-polysulfide redox couples that can readily interact with Li ions. The inverse vulcanization of the vinylene linking followed by the sulfurization-induced nucleophilic aromatic substitution reaction (SNAr) on the perfluorinated aromatic center of the COFs enabled the covalent trapping of cyclic-polysulfides. The experimentally observed reversible Li-interaction mechanism of these highly conjugated frameworks was computationally verified and supported by in situ Raman studies, demonstrating a significant reduction of polysulfide shuttle in a conventional Li-SB and opening the door for a COF-derived high-performing Li-OrSB

Sulfide Bridged Covalent Quinoxaline Frameworks for Lithium-Organo-Sulfide Battery

The chelating ability of quinoxaline cores and the redox activity of organo-sulfide bridges in layered covalent-organic frameworks (COFs) offer dual active sites for reversible lithium (Li)-storage. The designed COFs combining these properties feature disulfide and polysulfide-bridged networks showcasing an intriguing lithium-storage mechanism, which can be considered as a lithium-organo-sulfide (Li-OrS) battery. The experimental-computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to quinoxaline core enables a redox-mediated reversible cleavage of the sulfur-sulfur bond and the formation of covalently anchored lithium-sulfide chains or clusters during Li-interactions, accompanied by a marked reduction of Li-polysulfide (Li-PS) dissolution into the electrolyte, a frequent drawback of lithium-sulfur (Li-S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li-ion-organo-sulfide interactions. As a result, nearly 84% retention of specific capacity was observed at 100 mA/g for the polysulfide-bridged COF after 500 charge-discharge cycles. Thus, integrating redox-active organic-framework materials with covalently anchored sulfides enables a stable Li-OrS battery mechanism which shows benefits over a typical Li-S battery. This article is protected by copyright. All rights reserved