Polyoxometalate-Supported Bis(2,2′-bipyridine)mono(aqua)nickel(II) Coordination Complex: an Efficient Electrocatalyst for Water Oxidation

Abstract

A polyoxometalate (POM)-supported nickel(II) coordination complex, [Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·3HO (1; 2,2'-bpy = 2,2'-bipyridine), has been synthesized and structurally characterized. We could obtain a relatively better resolved structure from dried crystals of 1, Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·HO (D1). Because the title compound has been characterized with a {Ni(2,2'-bpy)(HO)} fragment coordinated to the surface of the Keggin anion ([H(CoWO]) via a terminal oxo group of tungsten and the [Ni(2,2'-bpy)] coordination complex cation sitting as the lattice component in the concerned crystals, the electronic spectroscopy of compound 1 has been described by comparing its electronic spectral features with those of [Ni(2,2'-bpy)(HO)Cl]Cl, [Ni(2,2'-bpy)]Cl, and K[CoWO]·6HO. Most importantly, compound 1 can function as a heterogeneous and robust electrochemical water oxidation catalyst (WOC). To gain insights into the water oxidation (WO) protocol and to interpret the nature of the active catalyst, diverse electrochemical experiments have been conducted. The mode of action of the WOC during the electrochemical process is accounted for by confirmation that there was no formation/participation of metal oxide during various controlled experiments. It is found that the title compound acts as a true catalyst that has Ni (coordinated to POM surface) acting as the active catalytic center. It is also found to follow a proton-coupled electron-transfer pathway (two electrons and one proton) for WO catalysis with a high turnover frequency of 18.49 (mol of O)(mol of Ni) s.

Synthesis of Extended Bipyridine‐proline Chiral Catalysts and Resulting Effects on the Asymmetric Aldol Reactions of Bulkier Aldehyde Derivatives with Cyclohexanone

“…For these reasons, a large number of chiral catalysts have been recently developed in asymmetric catalytic reactions and chiral recognition . As compared to that of chiral phosphine and amine catalysts, chiral bipyridine catalysts have attracted great attention owing to their highly efficient stereocontrol and unique coordination capabilities . Noticeably, a lot of reports indicated that the installation of an axially unfixed bipyridine in the designed organocatalysts may afford them favorable conformational properties responsible for efficient chiral induction, and therefore the effect of the steric hindrance originating from reactant or catalyst itself could be minimized .…”

Highly stable polyoxometalate‐resorcin[4]arene‐based inorganic‐organic complexes for catalytic oxidation desulfurization

“…Usually, POMs are employed as electrocatalysts owing to their structural stability after undergoing electron transfer processes . Considering the stability of 1 and 2 in a wide pH values, electrochemical experiments were conducted in 0.5 M H 2 SO 4 using modified carbon paste electrodes ( 1‐ CPE and 2‐ CPE).…”

Polyoxometalates: Tailoring metal oxides in molecular dimension toward energy applications

“…Because of the popularity of the NiO metal oxide in many energy applications, more researches should be carried out to synthesize and characterize the polyoxonickelates that combine the virtues of nickel oxide and molecular design flexibility. Nevertheless, nickel species are found to be common ingredient in many polyoxometalates for cluster functionalization . For example, polynuclear nickel clusters with Ni 12 , Ni 13 , and Ni 25 cores has been incorporated in polyoxometalate to act as water oxidation catalysts whereas the photocatalysis of Ni 2+ and NiO is ruled out .…”

“…Nevertheless, nickel species are found to be common ingredient in many polyoxometalates for cluster functionalization. 60,[150][151][152][153][154][155][156][157][158][159][160] For example, polynuclear nickel clusters with Ni 12 , Ni 13 , and Ni 25 cores has been incorporated in polyoxometalate to act as water oxidation catalysts whereas the photocatalysis of Ni 2+ and NiO is ruled out. 60 Ni 24 cages with calixarene and Pt clusters have been employed to activate the hydrogen evolution reaction.…”