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.

First Organic–Inorganic Hybrid Compounds Formed by Ge-V-O Clusters and Transition Metal Complexes of Aromatic Organic Ligands

Three compounds based on Ge-V-O clusters were hydrothermally synthesized and characterized by IR, UV-Vis, XRD, ESR, elemental analysis and X-ray crystal structural analysis. Both [Cd(phen)(en)]2[Cd2(phen)2V12O40Ge8(OH)8(H2O)]∙12.5H2O (1) and [Cd(DETA)]2[Cd(DETA)2]0.5[Cd2(phen)2V12O41Ge8(OH)7(0.5H2O)]∙7.5H2O (2) (1,10-phen = 1,10-phenanthroline, en = ethylenediamine, DETA = diethylenetriamine) are the first Ge-V-O cluster compounds containing aromatic organic ligands. Compound 1 is the first dimer of Ge-V-O clusters, which is linked by a double bridge of two [Cd(phen)(en)]2+. Compound 2 exhibits an unprecedented 1-D chain structure formed by Ge-V-O clusters and [Cd2(DETA)2]4+ transition metal complexes (TMCs). [Cd(en)3]{[Cd(η2-en)2]3[Cd(η2-en)(η2-μ2-en)(η2-en)Cd][Ge6V15O48(H2O)]}∙5.5H2O (3) is a novel 3-D structure which is constructed from [Ge6V15O48(H2O)]12− and four different types of TMCs. We also synthesized [Zn2(enMe)3][Zn(enMe)]2[Zn(enMe)2(H2O)]2[Ge6V15O48(H2O)]∙3H2O (4) and [Cd(en)2]2{H8[Cd(en)]2Ge8V12O48(H2O)}∙6H2O (5) (enMe = 1,2-propanediamine), which have been reported previously. In addition, the catalytic properties of these five compounds for styrene epoxidation have been assessed.

Soluble Hetero-Polyoxovanadates and Their Solution Chemistry Analyzed by Electrospray Ionization Mass Spectrometry

Polyoxometalates (POMs) are an intriguing class of compounds due to their tremendous structural variety and the wide spectrum of resulting properties, which make them interesting for applications in fields such as catalysis, material science or nanotechnology. Their ability to form large supramolecular architectures by self-assembly offers an entry to complex, functional systems. After an introduction into the structure and synthesis of POMs of the early transition metals, recently discovered water-soluble antimonato polyoxovanadates (Sb-POVs) and the investigation of their chemical reactivity are discussed. Electrospray ionization mass spectrometry (ESI-MS) is presented as an analytical technique suitable to investigate the structure of complex POM assemblies in solution and to probe the underlying reactivity and formation mechanisms. This Minireview highlights the first studies on the soluble Sb-POVs and how the knowledge of their reactivity obtained by ESI-MS has fostered the syntheses of numerous novel Sb-POV compounds.

Mixing SbIII and GeIV occupancy in the polyoxovanadate {V14E8} archetype

The first mixed germanato-antimonato derivative of the {V14E8O42} (E=semi-metal) cluster archetype has been synthesized under hydrothermal conditions and isolated as {Ni(phen)3}2[α-VIV 14SbIII 5GeIV 3O42(OH)3(H2O)]· ≈16H2O (phen=1,10-phenanthroline). In the cluster anion, seven of the eight hetero-metal positions are occupied by disordered Ge/Sb atoms, while one position is fully occupied by Sb atoms. The [V14Sb5Ge3O42(OH)3(H2O)]6− anions are arranged in pairs with remarkably short inter-cluster Sb···O contacts. Bond valence sum calculation strongly suggests that the Sb···O contact must be taken into account as a weak bond. The magnetic properties are dominated by strong intra-cluster antiferromagnetic exchange interactions, and the cluster anion is magnetically quasi-isolated from the spins of the Ni2+ complex cations.

A Series of Compounds Based on [P2W18O62]6- and Transition Metal Mixed Organic Ligand Complexes with High Catalytic Properties for Styrene Epoxidation

Seven compounds based on [P₂W₁₈O₆₂]^6- ({P₂W₁₈}) were successfully prepared and carefully characterized. [HC₅H₅N][Cu(2,2'-bpy)₂]₂[HP₂W₁₈O₆₂]·2H₂O (bpy = bipyridine) (1) is constructed from {P₂W₁₈} bridged by [Cu(2,2'-bpy)₂]²⁺. [HC₅H₅N][Zn(2,2'-bpy)₂]₂[HP₂W₁₈O₆₂]·4H₂O (1a) is isostructural and isomorphous with compound 1. [Cu₄(2,2'-bpy)₃(nic)₃(OH)₂(H₂O)][H₃P₂W₁₈O₆₂]·0.5H₂O (nic = nicotinic acid) (2) is formed by {P₂W₁₈} and tetracopper transition metal mixed organic ligand complexes (TMMCs). [Cu₂(2,2'-bpy)₂(C₂O₄)]₃[P₂W₁₈O₆₂]·3H₂O (3) is made up of {P₂W₁₈} and bicopper TMMCs, [Cu₆(2,2'-bpy)₆(OH)₆][P₂W₁₈O₆₂]·2H₂O (4) is built up from {P₂W₁₈}, and hexacopper complexes of 2,2'-bpy and hydroxyls. [Cu(2,2'-bpy)(hnic)_0.5][Cu₃(2,2'-bpy)₃(hnic)₂(H₂O)₂][H₃P₂W₁₈O₆₂] (hnic = hydroxyl nicotinic acid) (5a) contains two different TMMCs. In addition, compound 5a is the first example of a compound that contains Cu-π interactions. [Cu₂(2,2'-bpy)₂(hnic)][H₄P₂W₁₈O₆₂]· xH₂O ( x ≈ 50) (5b) is based on {P₂W₁₈} and [Cu₂(2,2'-bpy)₂(hnic)]²⁺. We discuss the mechanisms for the formations of these compounds. All the catalytic performances of the compounds for styrene epoxidation to styrene oxide are high.

A series of organic–inorganic hybrid compounds formed by [P2W18O62]6−and several types of transition metal complexes

A series of new organic–inorganic hybrid compounds based on [P₂W₁₈O₆₂]⁶⁻and several types of transition metal complexes have been synthesized and characterized.

An unprecedented antimonato-polyoxovanadate (SbPOV) based on both α-[V14Sb8O42]4− and β-[V14Sb8O42]4− isomers

An unprecedented antimonato-polyoxovanadate (SbPOV) based on both α-[V₁₄Sb₈O₄₂]⁴⁻ and β-[V₁₄Sb₈O₄₂]⁴⁻ isomers has been synthesized.