Thermodynamic properties of the aqueous sulfide and bisulfide ions and the second ionization constant of hydrogen sulfide over extended temperatures

Cobble, J. W.; Stephens, H.P.

doi:10.1021/ic50097a036

Cited by 17 publications

(1 citation statement)

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“…Polysulfide solutions were prepared by dissolving solid sulfur in aqueous sodium sulfide solutions. The solution chemistry is complex, but well understood. − The initial dissolution of Na 2 S in water produces an equimolar mixture of hydrosulfide ions HS – and hydroxide ions OH – : The addition of zerovalent sulfur (octasulfur) S 8 0 then produces polysulfide species S n 2– of various chain lengths n : Spectroscopic measurements indicate that the maximum chain length of polysulfide species that can form spontaneously at room temperature is n = 5. Longer chains are unstable, precipitating colloidal sulfur. − …”

Section: Methodsmentioning

confidence: 99%

Supercatalysis by Superexchange

Fletcher

Dijk

2016

J. Phys. Chem. C

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In modern transition state theory, the rate constant for an electron transfer reaction is expressed as the product of four factors: an exponential factor, a preexponential factor, an electronic transmission coefficient, and a nuclear transmission coefficient. The activation energy of the reaction manifests inside the exponential factor, and on the conventional view, catalysis occurs by decreasing this activation energy below its catalyst-free value. In the present work we report the discovery of an unusual counter-example in which catalysis occurs by increasing the electron transmission coefficient far above its catalyst-free value. The mechanism involves the formation of a superexchange bridge between an electron donor (a graphite cathode) and an electron acceptor (a pentasulfide ion). The bridge consists of a d z 2 orbital inside a cobalt phthalocyanine molecule. The dramatic result is the acceleration of the reduction of pentasulfide ions by more than 5 orders of magnitude compared with the catalyst-free case.

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