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Proton Conduction in a Single Crystal of a Phosphonato-Sulfonate-Based Coordination Polymer: Mechanistic Insight.

ABSTRACT: The proton conduction properties of a phosphonato-sulfonate-based coordination polymer are studied by impedance spectroscopy using a single crystal specimen. Two distinct conduction mechanisms are identified. Water-mediated conductance along the crystal surface occurs by mass transport, as evidenced by a high activation energy (0.54?eV). In addition, intrinsic conduction by proton 'hopping' through the interior of the crystal with a low activation energy (0.31?eV) is observed. This latter conduction is anisotropic with respect to the crystal structure and seems to occur through a channel along the c axis of the orthorhombic crystal. Proton conduction is assumed to be mediated by sulfonate groups and non-coordinating water molecules that are part of the crystal structure.

SUBMITTER: Javed A

PROVIDER: S-EPMC7187476 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Proton Conduction in a Single Crystal of a Phosphonato-Sulfonate-Based Coordination Polymer: Mechanistic Insight.

Javed Ali A Wagner Thorsten T Wöhlbrandt Stephan S Stock Norbert N Tiemann Michael M

Chemphyschem : a European journal of chemical physics and physical chemistry 20200224 7

The proton conduction properties of a phosphonato-sulfonate-based coordination polymer are studied by impedance spectroscopy using a single crystal specimen. Two distinct conduction mechanisms are identified. Water-mediated conductance along the crystal surface occurs by mass transport, as evidenced by a high activation energy (0.54 eV). In addition, intrinsic conduction by proton 'hopping' through the interior of the crystal with a low activation energy (0.31 eV) is observed. This latter conduc ...[more]

PMID: 32045082

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Project description:Ruthenium(II) complexes having pterins of redox-active heteroaromatic coenzymes as ligands were demonstrated to perform multistep proton transfer (PT), electron transfer (ET), and proton-coupled electron transfer (PCET) processes. Thermodynamic parameters including pK(a) and bond dissociation energy (BDE) of multistep PCET processes in acetonitrile (MeCN) were determined for ruthenium-pterin complexes, [Ru(II)(Hdmp)(TPA)](ClO(4))(2) (1), [Ru(II)(Hdmdmp)(TPA)](ClO(4))(2) (2), [Ru(II)(dmp(-))(TPA)]ClO(4) (3), and [Ru(II)(dmdmp(-))(TPA)]ClO(4) (4) (Hdmp = 6,7-dimethylpterin, Hdmdmp = N,N-dimethyl-6,7-dimethylpterin, TPA = tris(2-pyridylmethyl)amine), all of which had been isolated and characterized before. The BDE difference between 1 and one-electron oxidized species, [Ru(III)(dmp(-))(TPA)](2+), was determined to be 89 kcal mol(-1), which was large enough to achieve hydrogen atom transfer (HAT) from phenol derivatives. In the HAT reactions from phenol derivatives to [Ru(III)(dmp(-))(TPA)](2+), the second-order rate constants (k) were determined to exhibit a linear relationship with BDE values of phenol derivatives with a slope (-0.4), suggesting that this HAT is simultaneous proton and electron transfer. As for HAT reaction from 2,4,6-tri-tert-buthylphenol (TBP; BDE = 79.15 kcal mol(-1)) to [Ru(III)(dmp(-))(TPA)](2+), the activation parameters were determined to be DeltaH(double dagger) = 1.6 +/- 0.2 kcal mol(-1) and DeltaS(double dagger) = -36 +/- 2 cal K(-1) mol(-1). This small activation enthalpy suggests a hydrogen-bonded adduct formation prior to HAT. Actually, in the reaction of 4-nitrophenol with [Ru(III)(dmp(-))(TPA)](2+), the second-order rate constants exhibited saturation behavior at higher concentrations of the substrate, and low-temperature ESI-MS allowed us to detect the hydrogen-bonding adduct. This also lends credence to an associative mechanism of the HAT involving intermolecular hydrogen bonding between the deprotonated dmp ligand and the phenolic O-H to facilitate the reaction. In particular, a two-point hydrogen bonding between the complex and the substrate involving the 2-amino group of the deprotonated pterin ligand effectively facilitates the HAT reaction from the substrate to the Ru(III)-pterin complex.

Dataset Information

Proton Conduction in a Single Crystal of a Phosphonato-Sulfonate-Based Coordination Polymer: Mechanistic Insight.

Publications

Proton Conduction in a Single Crystal of a Phosphonato-Sulfonate-Based Coordination Polymer: Mechanistic Insight.

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