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.

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.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

POM-based MOFs simultaneously possessing the virtues of POMs and MOFs exhibit excellent heterogeneous catalytic properties.

Assembly, structures and properties of polyoxometalate-based supramolecular complexes involving in situ transformation of single-branch N-donor cyano ligands

A series of polyoxometalate-based supramolecular complexes were prepared with in situ transformation of single-branch N-donor cyano ligands, exhibiting diverse structures and good electrocatalytic and photocatalytic properties.

Two rare {M2(MoO4)2} n chain-containing molybdate-based metal-organic complexes with a bis-pyrazole-bis-amide ligand: fluorescent sensing and photocatalysis performance

By introducing a bis-pyrazole-bis-amide ligand, N,N′-bis(1H-pyrazole-4-carboxamide)-1,4-benzene (L), two molybdate-based metal–organic complexes containing {M₂(MoO₄)₂}_n (M = Co, Zn), [Co₂L₂(MoO₄)₂]·H₂O (1), [Zn₂L₂(MoO₄)₂]·H₂O (2), have been prepared under hydrothermal/solvothermal conditions. X-ray diffraction analyses reveal that both 1 and 2 are isostructural. An interesting structural feature is that a kind of {M₂(MoO₄)₂}_n chain could be found in 1 and 2, although different raw materials [Mo₇O₂₄]⁶⁻ and [PMo₁₂O₄₀]³⁻ anions were utilized. Then these chains are further linked by L ligands into a two dimensional (2D) structure. The title complexes represent the first examples containing {MoO₄} units and pyrazole-/or amide-derivative ligands. Complexes 1 and 2 exhibit distinct performances due to different metal centers, with 2 acting as a fluorescent sensor for Fe³⁺, MnO₄⁻, CrO₄²⁻ and Cr₂O₇²⁻, but 1 being a better photocatalyst towards degradation of cationic dyes methylene blue (MB) and neutral red (NR).

Two molybdate-based complexes containing {M₂(MoO₄)₂}_n (M = Co or Zn) chains were obtained, which demonstrated different properties: excellent photocatalytic degradation performance of cationic dyes for 1 and fluorescence sensing behavior for 2.

A novel sandwich shaped {CoIII2CoII12MoV24} cluster with a CoII4 triangle encapsulated in two capped CoIIICoII4MoV12O40 fragments

A novel discrete {Co₁₄Mo₂₄} nanoscaled cluster, with a triangle Co₄ core encapsulated in two novel capped Co-substituted Keggin-type Co₅Mo₁₂O₄₀ anions, was isolated from alkaline methanol solution. And the HRESI-MS of {Co₁₄Mo₂₄} cluster was recorded.

Three novel polyoxometalate-based inorganic–organic hybrid materials based on 2,6-bis(1,2,4-triazol-1-yl)pyridine

Three novel inorganic–organic hybrid materials [Co(btp)₂(W₅O₁₆)(H₂O)]_n (1), [Cd₃(btp)₆(PW₁₂O₄₀)₂(H₂O)₆·6H₂O]_n (2), and [Ag₃(btp)₂(PMo₁₂O₄₀)·1.5H₂O]_n (3) (btp = 2,6-bis(1,2,4-triazol-1-yl)pyridine) have been hydrothermally synthesized and characterized by IR spectroscopy, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), elemental analysis and thermal gravimetric analysis (TGA). The most striking structure feature of compound 1 is a 3D polycatenation framework, interpenetrated by a 2D 4-connected sql topology layer and a 3D 6-connected rob topology framework. Compound 2 exhibits a rare meso-helices 3D network with different chiralities crossing coexistence. Compound 3 also holds a 3D framework formed by linking terminal oxygen atoms of [α-PMo₁₂O₄₀]³⁻ anions and silver ions in a 2D metal–organic layer. Compound 1 displays antiferromagnetic behavior. The luminescence, electrochemical and photocatalytic properties of compounds 1–3 have also been investigated. Compound 3 exhibits significant electrochemical activity for the reduction of H₂O₂ while compounds 1 and 2 show efficient photocatalytic activities for the degradation of Rhodamine B (RhB). Furthermore, the three compounds display luminescence behaviors in the solid state.

Three novel inorganic–organic hybrid materials based on 2,6-bis(1,2,4-triazol-1-yl)pyridine have been synthesized with different polyanions and transition metal ions.

Various types of isopolymolybdate-based metal–organic complexes formed in different conditions: synthesis, structures, luminescence, electrochemical, and photocatalytic performances

A series of isopolymolybdate-based complexes of different metals and ligands were prepared, which exhibited different luminescence behaviors, current sensing activities, and photocatalytic MB performances.

Construction of d10 metal coordination polymers based on in situ formed 3,5-di(1H-1,2,4-triazol-1-yl)benzoic acid from different precursors: influence of in situ hydrolysis reactions on assembly process

Seven new d¹⁰ coordination polymers based on in situ formed HDTBA from two different precursors were obtained. The influence of in situ reaction on the assembly process was explored.

Various polyoxomolybdate-based hybrids induced by pH and solvents: structures, adsorption activities for dyes and bifunctional electrocatalytic properties

By changing the pH values and solvents, four different polyoxomolybdate hybrids were synthesized, which display good adsorption activities for different organic dyes and bifunctional electrocatalytic properties.