Designed Construction of Cluster Organic Frameworks from Lindqvist-type Polyoxovanadate Cluster

Using Coordination Chemistry to Control "Click" Reactions: The Selective Formation of Asymmetrically Ligated Polyoxometalates

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction between (NBu4)2[V6O13((OCH2)3CCH2N3)2] and 3-ethynylpyridine led to the formation of products capable of forming poorly soluble coordination compounds with transition metal ions such as Cu(I) and Zn(II). The formation of these poorly soluble phases is an important feature that was used to determine the course of reactions, allowing the selective preparation of symmetric bis-pyridyltriazolyl and asymmetric monopyridyltriazolyl derivatives with relatively high yields and high substrate conversions. The asymmetric compound (NBu4)2[V6O13((OCH2)3CCH2-N3C2H-C5H4N)((OCH2)3CCH2N3)] (V6asym) was utilized in the subsequent "click" postfunctionalization reaction with 1,4-diethynylbenzene, resulting in a covalently bound V6asym-V6asym dimer. This dimeric compound was subjected to scanning probe microscopy studies on gold surfaces, which revealed no electronic coupling between the hexavanadate cores within the dimer upon potential-induced switching. This observation indicates that such dimers and higher-order oligomers composed of polyoxometalate-ligand-polyoxometalate bridges can be exploited as active capacitor/memristor units, relevant to increase the data storage capacity of standard memory devices with innovative molecular switching mechanisms.

An Unusual Crystalline Porous Framework Constructed from Multitypes of Cages with Proton Conduction Property and Heterogeneous Catalytic Activity for Pyrazole Synthesis

An unusual crystalline porous framework constructed from four types of cages, including all-inorganic Keggin-type polyoxometalate (POM) cages [H3W12O40]5-, organic hexamethylenetetramine (Hmt) cages, nanosized silver-Hmt coordination cages, and giant POM-silver-Hmt cages, was hydrothermally synthesized and structurally characterized. The framework features a highly symmetrical structure with one-dimensional nanoscale channels and holds good thermal/solvent stability, which endow it with proton conduction properties and heterogeneous catalytic activity for pyrazole. This paper not only contributes to broadening the structural diversity of cage-based crystalline porous framework materials but also sheds new light on the design of new functional framework materials.

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.

Rational synthesis of elusive organic-inorganic hybrid metal-oxo clusters: formation and post-functionalization of hexavanadates

Paving the way towards new functional materials relies increasingly on the challenging task of forming organic-inorganic hybrid compounds. In that regard, discrete atomically-precise metal-oxo nanoclusters have received increasing attention due to the wide range of organic moieties that can be grafted onto them through functionalization reactions. The Lindqvist hexavanadate family of clusters, such as [V₆O₁₃{(OCH₂)₃C-R}₂]^2- (V₆-R), is particularly interesting due to the magnetic, redox, and catalytic properties of these clusters. However, compared to other metal-oxo cluster types, V₆-R clusters have been less extensively explored, which is mainly due to poorly understood synthetic challenges and the limited number of viable post-functionalization strategies. In this work, we present an in-depth investigation of the factors that influence the formation of hybrid hexavanadates (V₆-R HPOMs) and leverage this knowledge to develop [V₆O₁₃{(OCH₂)₃CNHCOCH₂Cl}₂]^2- (V₆-Cl) as a new and tunable platform for the facile formation of discrete hybrid structures based on metal-oxo clusters in relatively high yields. Moreover, we showcase the versatility of the V₆-Cl platform through its post-functionalization via nucleophilic substitution with various carboxylic acids of differing complexity and with functionalities that are relevant in multiple disciplines, such as supramolecular chemistry and biochemistry. Hence, V₆-Cl was shown to be a straightforward and versatile starting point for the formation of functional supramolecular structures or other hybrid materials, thereby enabling their exploration in various fields.

Discrete Arsonate-Grafted Inverted-Keggin 12-Molybdate Ion [Mo12O32(OH)2(4-N3C2H2-C6H4AsO3)4]2- and Formation of a Copper(II)-Mediated Metal-Organic Framework

The discrete inverted-Keggin ion [Mo₁₂O₃₂(OH)₂(4-N₃C₂H₂-C₆H₄AsO₃)₄]^2- (1) has been prepared in an aqueous acidic (pH 0.8) medium by the reaction of MoO₃ with the (4-triazolylphenyl)arsonic acid 4-N₃C₂H₂-C₆H₄AsO₃H₂ under hydrothermal conditions and was isolated as a sodium salt in 21% yield. The exact same reaction in the presence of Cu²⁺ ions resulted in the neutral metal-organic framework (MOF) Cu₂[Mo₁₂O₃₄(4-N₃C₂H₂-C₆H₄AsO₃)₄] (Cu-1) in 68% yield. The inverted-Keggin ion 1 comprises a metal-oxo core, which is capped by four organoarsonate groups, and in Cu-1, individual polyanions are linked in the solid state by coordination of the Cu²⁺ ions with the triazolyl groups. The discrete ion 1 was characterized by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic absorption (AA) spectroscopy, as well as thermogravimetric analysis (TGA), and the POM-MOF Cu-1 was characterized by single-crystal and powder XRD, FT-IR, TGA, and gas sorption. Cu-1 has channels with a diameter of around ∼0.9 nm and exhibits a water-vapor adsorption capacity of 89.7 cm³ g^-1 (p/p₀ = 0.95).

Lanthanide-Anderson Polyoxometalates Frameworks: Efficient Sulfide Photooxidation

Three polyoxometalate-based metal-organic frameworks were synthesized by the thermal reaction of pyridyl-Anderson polyoxometalate linker and lanthanide ions. With the help of [Ru(bpy)₃]²⁺ photosensitizer, these frameworks exhibited excellent photocatalytic sulfide oxidation performance with sulfoxide selectivity. The reactive oxygen species as well as the photooxidation mechanism were also explored.

Designed Syntheses of Three {Ni6PW9}-Based Polyoxometalates, from Isolated Cluster to Cluster-Organic Helical Chain

Three new hexa-Ni-substituted Keggin-type polyoxometalates (POMs), [Ni6(OH)3- (DACH)3(H2O)6(PW9O34)]·31H2O (1), [Ni(DACH)2][Ni6(OH)3(DACH)3(HMIP)2(H2O)2(PW9O34)]·56 H2O (2), and [Ni(DACH)2][Ni6(OH)3(DACH)2(AP)(H2O)5(PW9O34)]·2H2O (3) (DACH = 1,2-Diami- nocyclohexane, MIP = 5-Methylisophthalate, AP = Adipate) were successfully made in the presence of DACH under hydrothermal conditions. 1 is an isolated hexa-Ni-substituted Keggin unit decorated by DACH. In order to further construct POM cluster-organic frameworks (POMCOFs) on the basis of 1, by analyzing the steric hindrances and orientations of the POM units, the rigid HMIP and flexible AP ligands were successively incorporated, and another anionic monomeric POM 2 and the new 1D POM cluster organic chain (POMCOC) 3 were obtained. HMIP ligand still acts as a decorating group on the Ni6 core of 2 but results in the different spatial arrangement of the {Ni6PW9} units. AP ligands in 3 successfully bridge adjacent isolated POM cluster units to 1D POMCOC with left-hand helices. The AP in 3 is the longest aliphatic carboxylic acid ligand in POMs, and the 1D POM cluster-AP helical chain represents the first 1D POMCOC with a helical feature.

Chiral {Ni6PW9} Cluster-Organic Framework: Synthesis, Structure, and Properties

A chiral three-dimensional polyoxometalate cluster-organic framework (POMCOF) H₃[(btc)Ni₆(μ₃-OH)₃(H₂O)₅(B-α-PW₉O₃₄)]·17H₂O (1, btc = 1,2,4-benzenetricarboxylate) has been made under hydrothermal conditions in the absence of amine or chiral starting reagents. 1 shows high stability in CH₃CN/DMF (1:3), acidic, and basic solutions with the pH ranging from 2 to 12 for 5 days. The UV-vis reflectance spectra and Mott-Schottky measurements reveal that 1 could be a suitable catalyst for photocatalysis. Visible-light-driven H₂ evolution studies have demonstrated that 1 is an ecofriendly, efficient, and recyclable catalyst with a H₂ evolution rate of 1058.24 μmol h^-1g^-1. Nonlinear optical (NLO) measurement reveals that 1 exhibits a second-harmonic generation (SHG) response of about 1.4 times that of KH₂PO₄ (KDP), indicating that 1 is a potential NLO material as well.

What is the maximum charge uptake of Lindqvist-type polyoxovanadates in organic–inorganic heterostructures?

One of the striking characteristics of the tris(alkoxo)-ligated Lindqvist-type polyoxovanadates [VV6O13{(OCH2)3CR}2]2− in highest oxidation state in solution is the ease of their chemical post-functionalization via the R group.

Four Inorganic-Organic Hybrid Borates: From 2D Layers to 3D Oxoboron Cluster Organic Frameworks

Four inorganic-organic hybrid borates, K[B₆O₉(OH)(en)]·H₂O (1, en = ethylenediamine), K[B₆O₉(OH)(1,3-dap)]·H₂O (2, 1,3-dap = 1,3-diaminopropane), K[B₆O₉(OH)(1,6-dah)_0.5]·H₂O (3, 1,6-dah = 1,6-diaminlhexane) and [(1,3-dap)Cd@B₅O₈(OH)]·0.5H₂O (4), were made under solvothermal conditions. 1 and 2 are isostructural and feature a 2D layer built by B₆O₉(OH) clusters and modified by en and 1,3-dap via B-N-C linkages. By replacing en and 1,3-dap with longer and more flexible 1,6-dah, a new type of oxoboron cluster organic framework 3 was obtained, which was composed of the same B₆O₉(OH) cluster layers as in 1 and 2 and 1,6-dah linkers. By replacing alkali metal K with transition metal Cd under similar synthetic conditions, another type of oxoboron cluster organic framework 4 was made in which the Cd-centered wheel cluster layers and 1,3-dap linkers were connected via Cd-N-C linkages.

A series of organic hybrid polyoxovanadate clusters incorporating tris(hydroxymethyl)methane derivatives

A series of new organic hybrid polyoxovanadate clusters [V₄O₄(μ-OH)₂(acac)₂(Htri)₂] (1, H₃tri = tris(hydroxymethyl) aminomethane, acac = acetylacetone), [V₄O₄(acac)₂(Htri)₂(L)₂] {HL = methanol (2), ethanol (3a and 3b), ethylene glycol (4) and benzyl alcohol (5)}, {V₄O₄(H₂O)₂(tri-acetamide)₂(CH₃COO)₂} (6, H₃tri-acetamide = N-(2-hydroxy-1,1-bis-hydroxymethyl-ethyl)-acetamide), [V₆O₈(μ-OH)₂(Htri)₃]·6H₂O (7) and [V₁₄O₁₈(tri)₂(Htri)₆(HCOO)(CH₃COO)]·2H₂O (8) were prepared by hydro(solvo)thermal methods and characterized structurally. 1 contains [VO(OH)(acac)] and [VO₂(Htri)] units, which are further interconnected via common edges to build a tetravanadyl cluster [V₄O₄(OH)₂(acac)₂(Htri)₂] with the double-deficient cube [V₄O₆]. The tetravanadyl cluster frameworks of 2-5 can be derived from the tetravanadyl cluster of 1 by replacing two -OH groups with two deprotonated organic alcohol ligands, namely, CH₃O^- (2), CH₃CH₂O^- (3a and 3b), HO(CH₂)₂O^- (4) and C₆H₅CH₂O^- (5). Interestingly, both 3a and 3b have the same chemical structure, but they exhibit different conformational polymorphisms [denoted as α-type (3a) and β-type (3b)]. Such conformational polymorphisms within the polyoxovanadate clusters incorporating tris(hydroxymethyl)methane derivatives emerged for the first time. 6 displays another tetravanadyl cluster {V₄O₄(H₂O)₂(tri-acetamide)₂(CH₃COO)₂} with a [V₄O₁₆] fragment, where the tri-acetamide unit comes from the amidation reaction of H₃tri and acetic acid and caps the tetrahedral void of the tetravanadyl cluster. The polyoxovanadate cluster of 7 can originate from the Lindqvist-type hexavanadyl cluster [V₆O₁₉] by replacing nine μ-oxides with nine alkoxides of three tri-acetamide^3- ligands. 8 exhibits a fully reduced tetradecavanadyl cluster based on the linkage of two heptavanadyl clusters via two O bridges. The magnetic properties of 1-8 show typical antiferromagnetic interactions.

Nicotinic-Acid-Ornamented Tetrameric Rare-Earth-Substituted Phospho(III)tungstates with the Coexistence of Mixed Keggin/Dawson Building Blocks and Its Honeycomb Nanofilm for Detecting Toxins

A fascinating class of nicotinic-acid-ornamented tetrameric rare-earth (RE)-substituted phospho(III)tungstates [NH₂(CH₃)₂]₁₀Na₄H₈[RE₂(NA)(HNA)(H₂O)₆(W₂O₄)(β-H₂P₂^IIIW₁₃O₄₉)(α-HP^IIIW₉O₃₃)]₂·22 H₂O [RE = Nd³⁺ (1-Nd), Tb³⁺ (2-Tb), Dy³⁺ (3-Dy), Ho³⁺ (4-Ho), HNA = nicotinic acid] were isolated through a one-step reaction method of Na₂WO₄·2H₂O, H₃PO₃, HNA, NH₂(CH₃)₂·HCl, and RE(NO₃)·6H₂O. Of meticulous concern is that HPO₃^2- was used as a template to construct tetrameric RE-substituted phospho(III)tungstates including mixed heteropolyoxotungstate building blocks. Their hybrid polyoxoanions are composed of two symmetrical [RE₂(NA)(HNA)(H₂O)₆(W₂O₄)(β-H₂P₂^IIIW₁₃O₄₉)(α-HPW₉O₃₃)]^11- units linked by RE-O-W bonds. The symmetrical unit consists of one peculiar heterometal nicotinic-acid-ornamented [RE₂(NA)(HNA)(W₂O₄)]⁹⁺ cluster connecting a pentavacant Dawson-like [β-H₂P₂W₁₃O₄₉]^12- and a trivacant Keggin [α-HPW₉O₃₃]^8- subunits. Furthermore, dimethyldioctadecylammonium chloride (DMDODA·Cl) was used to combine with 1-Nd in the CHCl₃-H₂O system through electrostatic interactions, leading to the 1-Nd@DMDODA composite material. The honeycomb-patterned film of the 1-Nd @DMDODA composite material was successfully constructed by using the breath figure method on a glassy carbon electrode, which can offer abundant binding sites to Au nanoparticles (nano-Au). Ulteriorly, Au-functionalized 1-Nd@DMDODA-modified electrode was utilized as an electrochemical sensor to detect ochratoxin A, showing a good detection limit of 1.19 pM.

3d-4f Heterometallic cluster incorporated polyoxoniobates with magnetic properties

A series of 3d-4f heterometallic cluster incorporated polyoxoniobates (PONbs) with different magnetic properties were first made and characterized. This work not only provides a promising strategy to make new heterometallic cluster incorporated PONbs but also demonstrates an ideal model to probe how transition-metal ions influence the magnetic property of PONbs.

Organo-functionalized polyoxovanadates: crystal architecture and property aspects

Polyoxovanadates (POVs), as one of the most prominent members of polyoxometalates (POMs), have been subject to extensive studies by virtue of their aesthetically intriguing structures and potential applications in catalysis, magnetism, and optics, among others. In recent years, organo-functionalized POVs have received considerable attention due to the combination of the advantages of POVs with the importance of organic species. In this review, the key developments of polyoxovanadates and, particularly, the achievements that are related to polyoxovanadates modified with organic ligands and transition metal-organic ligand are summarized. Herein, we systematically introduce the structural features of organo-functionalized POVs and their main applications involved in the magnetism and catalysis aspects. Finally, the current challenges and future prospects in the design, synthesis, and property investigation of polyoxovanadates are also discussed.

Molecular Vanadium Oxides for Energy Conversion and Energy Storage: Current Trends and Emerging Opportunities

Molecular vanadium oxides, or polyoxovanadates (POVs), have recently emerged as a new class of molecular energy conversion/storage materials, which combine diverse, chemically tunable redox behavior and reversible multielectron storage capabilities. This Review explores current challenges, major breakthroughs, and future opportunities in the use of POVs for energy conversion and storage. The reactivity, advantages, and limitations of POVs are explored, with a focus on their use in lithium and post-lithium-ion batteries, redox-flow batteries, and light-driven energy conversion. Finally, emerging themes and new research directions are critically assessed to provide inspiration for how this promising materials class can advance research in sustainable energy technologies.

Facile syntheses of silver thioantimonates exhibiting second-harmonic generation responses and large birefringence

Two chalcogenide crystalline compounds, [enH2][Ag4Sb2S6] (en = ethylenediamine) and [enH][Ag2SbS3], have been successfully synthesized by mild ionothermal and solvothermal means. [enH][Ag2SbS3] crystallizes in the noncentrosymmetric (NCS) and polar space group Pc, and its linear and nonlinear optical (NLO) properties have been investigated for the first time. Second harmonic generation (SHG) measurements revealed that [enH][Ag2SbS3] affords powder SHG performance values of 2.5 × KDP @1064 nm and 0.2 × AgGaS2 @2100 nm. Additional particle size vs. SHG efficiency measurements indicate that [enH][Ag2SbS3] is phase-matchable. The calculated birefringence Δn is 0.177 at 1064 nm, which is sufficiently large (the largest value among NCS thioantimonates) to achieve phase matching. [enH2][Ag4Sb2S6] crystallizes in the centrosymmetric space group P21/c and its structure features a double-layered variant honeycomb-like anionic network parallel to the ac plane separated by [enH2]2+ cations. The optical band gaps of [enH2][Ag4Sb2S6] and [enH][Ag2SbS3] are found to be 2.37 and 2.53 eV, respectively. Theoretical studies using density functional theory have been implemented to further elucidate the relationship between the band structure and NLO properties in [enH][Ag2SbS3].

Sn6 and Na4 Oxo Clusters Based Non-centrosymmetric Framework for Solution Iodine Absorption and Second Harmonic Generation Response

A three-dimensional non-centrosymmetric cluster organic framework has successfully been built from the {Sn₆} and {Na₄} cluster units via the oxalate ligand, which belongs to the first 3D framework containing different cluster units in the field of tin-oxo clusters. Besides the interesting structural characteristics, the obtained 3D framework not only can efficiently adsorb the iodine molecules but also displays the second harmonic generation response under the 1064 nm Q-switch laser.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

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

A bi-polyoxometallate-based host-guest metal-organic framework

Anionic POMs prefer to bond with positive metal cations instead of neutral or negative organic ligands. Therefore, it is challenging to synthesize POM-based MOFs, let alone bi-POM-based host-guest MOFs. In this work, an unprecedented bi-POM-based host-guest MOF, Na[Ni(enMe)2]4[Ni(enMe)2(H2O)2]2{[Ni6(μ3-OH)3(enMe)3 (SIP)1.5(B-α-PW9O34)]2[H3PNiW11O40]}·5enMe·33H2O (1), with Ni6-capped [PW9O34] as the node of the host framework and Keggin-type [PNiW11O40] units as the guest was synthesized. 1 showed excellent chemical stability towards aqueous solutions of pH 2-12 at both ambient and boiling temperature, providing opportunities for its application in fresh water harvesting from air.

A new type of composite MOFs based on high-valent Sb(v)-based units and cuprous-halide clusters

An unusual high-valent Sb(v)-based unit [SbL₂]^- (L = 2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol) was developed for the first time to combine with various cuprous-halide clusters for the construction of a brand-new class of heterometallic MOFs. This work not only promotes the limited development of Sb-based MOFs, but also provides a practical strategy for developing new types of composite materials.

Syntheses, structures and catalytic properties of Evans–Showell-type polyoxometalate-based 3D metal–organic complexes constructed from the semi-rigid bis(pyridylformyl)piperazine ligand and transition metals

Two 3D Evans–Showell-type POM-based different transition metals–bis-pyrazine–bis-amide complexes act as heterogeneous catalysts for the oxidation of benzyl alcohol.

Inorganic–organic hybrid high-dimensional polyoxotantalates and their structural transformations triggered by water

In this work, novel dimeric polyoxotantalate (POTa) clusters {Cu(en)(Ta₆O₁₉)}₂/{Cu(enMe)(Ta₆O₁₉)}₂ were introduced as SBUs to construct a new family of extended POTa materials, including the first two 3D POTa frameworks and two 2D POTa layers.