Capped Polyoxometalate Pillars between Metal–Organic Layers for Transferring a Supramolecular Structure into a Covalent 3D Framework

Abstract

Two robust metal-organic frameworks (MOFs), {H[Ni(π-HO)][Ni(rt-HO)]Ni(Tri)}[VWO]·24HO (1) and {H[Ni(π-O)][Ni(rt-HO)]Ni(Tri)}[VWVOV][VWVOV]·24HO (2) (Tri = 1,2,4-triazole), composed of polyoxometalates (POMs) and metal-organic units, were designed and synthesized by a hydrothermal method. Structure analysis indicates that there is a metal-organic crown [{Ni(Tri)(HO)}] ({Ni}) in these two compounds. In 1, the {Ni} crown embraces four pendant Tri ligands that could capture a cationic [Ni(HO)] group, resulting in the Ni-Tri building unit [Ni(HO){Ni(Tri)(HO)}] ({Ni}). The {Ni} building unit was fused together by Tri bridges into the 2D metal-organic layers, which are pillared by a typical Keggin-type POM [VWO] to construct a 3D supramolecular framework via the hydrogen bonds. Interestingly, the 2D metal-organic layer in 1 was successfully transferred into a 3D covalent MOF via extension of the length of the pillars by capping a Keggin-type POM with V-O units. Moreover, electrochemical behaviors and electrocatalytic properties of these two compounds were both studied, which can act as bifunctional electrocatalysts toward the reduction of HO and oxidation of nitrite in neutral aqueous solution.

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.…”

Heightened Integration of POM‐based Metal–Organic Frameworks with Functionalized Single‐Walled Carbon Nanotubes for Superior Energy Storage

“…Polyoxometalates (POMs) are a class of early transition metal anionic clusters with highly negative charges, strong stability, and tunable redox properties, which have been attracting considerable interests in their numerous applications in catalysis, magnetism, and energy conversion . Accompanying with, POM‐based extended structures such as transition metal‐substituted POMs, sulfate‐centered Preyssler‐type POMs, and vanadium‐capped POMs have also been explored with promising performances. Particularly, POMs show great potential in anode‐active materials in view of the characteristics of cluster‐type open framework and multi‐electron redox center, such as P‐based [PMo 12 O 40 ] 3− endowed as an “electron sponge” exhibiting a high capacity in LIBs due to the multi‐electron reversible transfer .…”