Three Polyoxovanadates-Based Organic-Inorganic Hybrids: Structural Variation, Bifunctional Electrocatalytic Activities, and Computational Studies

Experimental and Theoretical Study of Two 3D Difunctional Electrocatalytic Hybrid Vanadate-Containing Metal-Organic Motifs

Two novel 3D inorganic-organic hybrids based on [V6O18]6-/[V3O9]3- clusters, [Cu18(bbpy)18(V6O18)6]·3H2O (1) and [Cu4Ag4(pty)4(V3O9)4]·H2O (2) (bbpy = 3,5-bis(1-benzimidazole) pyridine, pty = 4'-(4″-pyridyl)-2,2':6',2″-terpyridine), were isolated in the same POV/Cu/N-heterocycle ligand reaction systems. Hybrids 1 and 2 possess novel three-dimensional bimetallic frameworks derived from [V6O18]6-/[V3O9]3- clusters and Cu-organic complexes. In 1, bbpy ligands are grafted by Cu2+ to a grid ribbon 2D sheet, which are connected with benzene-like [V6O18]6- to yield a 3D framework. In 2, helical {O-V-O-V-}n chains are bridged by Cu(II) ions into a 2D layer including eight-membered rings {V6Cu2} and six-membered rings {V4Cu2}, and the adjoining sheets are joined by Ag-N coordination bonds to form a framework structure. Moreover, hybrid 1 has superior electrocatalytic properties for nitrite reduction and oxidation of ascorbic acid with electrocatalytic efficiencies of 397.2 and 96%, respectively. Hybrid 2 displays coordinated electrocatalytic performance toward oxidation reaction through V and Cu centers. Meanwhile, the corresponding theoretical studies were conducted to evaluate electrocatalytic active sites and charge distribution.

Recent advances in oxidative catalytic applications of polyoxovanadate-based inorganic-organic hybrids

Polyoxovanadates (POVs) have received widespread attention in catalytic applications due to their various structures and remarkable redox properties. By introducing a second transition metal, POV-based inorganic-organic hybrid (POVH) catalysts show increasing stability and more catalytic active sites compared with pure POVs. In this perspective article, POVH materials as oxidative catalysts have been classified into two main categories according to the interactions between transition metal-complex units and POV clusters: (i) hybrids with metal-organic units act as isolated cations and (ii) hybrids with an organic ligand coordinate to the second transition metal, which is further linked to a POV cluster via oxygen bridges directly or indirectly to give zero-, one-, two- or three-dimensional supramolecular structures. The oxidative conversion of organic compounds, including thiophene derivatives, thioethers, alkanes, alcohols, and alkenes, and oxidative detoxification of a sulfur mustard simulant or degradation of lignin, along with the oxidative photo/electrocatalytic transformation of organic compounds catalyzed by POVH materials, are discussed in detail. Furthermore, the challenges and prospects toward the development of POVH catalysts are explored briefly from our perspectives.

Recent reports on vanadium based coordination polymers and MOFs

Coordination polymers (CP) and metal-organic frameworks (MOF) have become a topic of immense interest in this century primarily because of the structural diversity that they offer. This structural diversity results in their multifaceted utility in various fields of science and technology such as catalysis, medicine, gas storage or separation, conductivity and magnetism. Their utility inspires a large variety of scientists to engage with them in their scientific pursuit thus creating a buzz around them in the scientific community. Metals capable of forming CPs and MOFs are primarily transition metals. Among them vanadium-based CPs and MOFs demand detailed discussion because of the unique nature of vanadium which makes it stable in many oxidation states and coordination number. Vanadium’s versatility imparts additional structural marvel and usefulness to these CPs and MOFs.

Two polymolybdate-directed Zn(ii) complexes tuned by a new bis-pyridine-bis-amide ligand with a diphenylketone spacer for efficient ampere sensing and dye adsorption

Two polymolybdate-based Zn(ii) complexes were constructed from a new bis-pyridine-bis-amide ligand, which can be used as electrocatalysts and electrochemical sensors for Cr(vi), KBrO3, H2O2 and AA, and exhibit selective adsorption of CV and MB.

Capped Keggin Type Polyoxometalate-Based Inorganic-Organic Hybrids Involving In Situ Ligand Transformation as Supercapacitors and Efficient Electrochemical Sensors for Detecting Cr(VI)

To construct polyoxometalate-based complexes as electrode materials for supercapacitors and electrochemical sensors, we intentionally used in situ ligand transformation during the reaction. Two complexes based on polyoxometalates capped by zinc ions, H{Zn₄(DIBA)₄[(DIBA)(HPO₂)]₂(α-PMo^VI₈Mo^V₄O₄₀Zn₂)} (1) and [ε-PMo^V₈Mo^VI₄O₃₇(OH)₃Zn₄(HDBIBA)₂]·6H₂O (2) [DIBA = 3,5-di(1H-imidazol-1-yl)benzoic acid, and DBIBA = 3,5-bis(1H-benzoimidazol-1-yl)benzoic acid], have been prepared successfully. The DIBA and DBIBA ligands were generated in situ from initial materials 3,5-di(1H-imidazol-1-yl)benzonitrile and 3,5-di(1H-benzoimidazol-1-yl)benzonitrile. The three-dimensional structure of 1 consisted of two-dimensional interpenetrating layers and polyoxometalate-based chains composed of bicapped α-PMo₁₂Zn₂ polyoxoanions and phosphite-modified DIBA ligands. In 2, a kind of tetracapped ε-PMo₁₂Zn₄ polyoxoanion exists, which was further linked by DBIBA ligands into a one-dimensional chain. Two complexes could be employed as not only electrode materials for supercapacitors with specific capacitances of 171.17 F g^-1 for 1 and 146.77 F g^-1 for 2 at 0.5 A g^-1 but also efficient electrochemical sensors for detecting Cr(VI) with excellent limits of detection of 0.026 μM for 1 and 0.035 μM for 2, which represents a hopeful approach for exploiting polyoxometalate-based complexes as supercapacitor and electrochemical sensor materials.