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An unexpected oxidation: NaK₅Cl₂(S₂O₆)₂ revisited.

ABSTRACT: The title compound, NaK₅Cl₂(S₂O₆)₂ [systematic name: sodium penta-potassium dichloride bis-(di-thio-nate)], arose as an unexpected product from an organic synthesis that used di-thio-nite (S₂O₄^2-) ions as a reducing agent to destroy excess permanganate ions. Compared to the previous study [Stanley (1953 ?). Acta Cryst.6, 187-196], the present tetra-gonal structure exhibits a root 2a × root 2a × c super-cell due to subtle changes in the orientations of the di-thio-nate anions. The structure can be visualized as a three-dimensional framework of [001] columns of alternating trans-NaO₄Cl₂ and KO₄Cl₂ octa-hedra cross-linked by the di-thio-nate ions with the inter-stices occupied by KO₆Cl₂ polyhedra to generate a densely packed three-dimensional framework. The asymmetric unit comprises two sodium ions (site symmetries 4 and -4, four potassium ions (site symmetries = -4, 4, 1 and 1), three chloride ions (site symmetries = 4, 4 and 2) and two half-di-thio-nate ions (all atoms on general positions). Both di-thio-nate ions are completed by crystallographic inversion symmetry. The crystal chosen for data collection was found to be rotationally twinned by 180° about the [100] axis in reciprocal space with a 0.6298?(13):0.3702?(13) domain ratio.

SUBMITTER: Harrison WT

PROVIDER: S-EPMC5290562 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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An unexpected oxidation: NaK5Cl2(S2O6)2 revisited.

Harrison William T A WT Plater M John MJ

Acta crystallographica. Section E, Crystallographic communications 20170113 Pt 2

The title compound, NaK5Cl2(S2O6)2 [systematic name: sodium penta-potassium dichloride bis-(di-thio-nate)], arose as an unexpected product from an organic synthesis that used di-thio-nite (S2O42-) ions as a reducing agent to destroy excess permanganate ions. Compared to the previous study [Stanley (1953 ▸). Acta Cryst.6, 187-196], the present tetra-gonal structure exhibits a root 2a × roo ...[more]

PMID: 28217339

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Project description:Photochemical CO2 reduction catalysed by trans(Cl)-Ru(bpy)(CO)2Cl2 (bpy = 2,2'-bipyridine) efficiently produces carbon monoxide (CO) and formate (HCOO-) in N,N-dimethylacetamide (DMA)/water containing [Ru(bpy)3]2+ as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor. We have unexpectedly found catalyst concentration dependence of the product ratio (CO/HCOO-) in the photochemical CO2 reduction: the ratio of CO/HCOO- decreases with increasing catalyst concentration. The result has led us to propose a new mechanism in which HCOO- is selectively produced by the formation of a Ru(i)-Ru(i) dimer as the catalyst intermediate. This reaction mechanism predicts that the Ru-Ru bond dissociates in the reaction of the dimer with CO2, and that the insufficient electron supply to the catalyst results in the dominant formation of HCOO-. The proposed mechanism is supported by the result that the time-course profiles of CO and HCOO- in the photochemical CO2 reduction catalysed by [Ru(bpy)(CO)2Cl]2 (0.05 mM) are very similar to those of the reduction catalysed by trans(Cl)-Ru(bpy)(CO)2Cl2 (0.10 mM), and that HCOO- formation becomes dominant under low-intensity light. The kinetic analyses based on the proposed mechanism could excellently reproduce the unusual catalyst concentration effect on the product ratio. The catalyst concentration effect observed in the photochemical CO2 reduction using [Ru(4dmbpy)3]2+ (4dmbpy = 4,4'-dimethyl-2,2'-bipyridine) instead of [Ru(bpy)3]2+ as the photosensitizer is also explained with the kinetic analyses, reflecting the smaller quenching rate constant of excited [Ru(4dmbpy)3]2+ by BNAH than that of excited [Ru(bpy)3]2+. We have further synthesized trans(Cl)-Ru(6Mes-bpy)(CO)2Cl2 (6Mes-bpy = 6,6'-dimesityl-2,2'-bipyridine), which bears bulky substituents at the 6,6'-positions in the 2,2'-bipyridyl ligand, so that the ruthenium complex cannot form the dimer due to the steric hindrance. We have found that this ruthenium complex selectively produces CO, which strongly supports the catalytic mechanism proposed in this work.

Dataset Information

An unexpected oxidation: NaK₅Cl₂(S₂O₆)₂ revisited.

Publications

An unexpected oxidation: NaK<sub>5</sub>Cl<sub>2</sub>(S<sub>2</sub>O<sub>6</sub>)<sub>2</sub> revisited.

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