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Introducing functional groups at different stages in the assembly of a metal–organic cage has led to two distinct, endo-functionalized products, a result attributed to kinetic trapping in a process generally operating under thermodynamic control.

Here we report the formation of giant {Mo

The structurally new, carbon-free pentadecanuclear Fe-containing polyoxometalate, Na21[NaFe15(OH)12(PO4)4(A-α-SiW9O34)4]·85H2O (Na21-Fe15P4(SiW9)4), was synthesized using a facile one-pot, solution-based synthetic approach and systematically characterized by various spectroscopic techniques. Single-crystal X-ray diffraction reveals that the title complex is composed of two [Fe4(A-α-SiW9O34)] fragments and two [Fe3.5(A-α-SiW9O34)] fragments stabilized by four PO4 linkers in a tetrameric style with idealized Td point group symmetry. When coupling with (4,4'-ditert-butyl-2,2'-dipyridyl)-bis(coumarin)-iridium(III) hexafluorophosphate ([Ir(coumarin)2(dtbbpy)][PF6]) photosensitizer and triethanolamine (TEOA) sacrificial electron donor, polyoxoanion Fe15P4(SiW9)4 effectively catalyzed hydrogen production with a minimally optimized TON of 986, which represents, to our knowledge, one of the highest values among known Fe-substituted POM-catalyzed hydrogen production systems. Both a mercury-poisoning test and FT-IR characterizations proved the structural stability of Fe15P4(SiW9)4 catalyst under photocatalytic conditions. The photocatalytic mechanism of the present hydrogen-evolving system was investigated by time-solved luminescence and static emission quenching measurements.

Developing portable membrane sensors to accurately detect the biomolecule ascorbic acid (AA) is extremely important for food safety and human health. Herein, we successfully design and synthesize a novel cationic metal organic framework (Eu-pbmc, Hpbmc = 2-(pyridine-2-yl)-1H-benzimidazole-5-carboxylic acid) and assemble polyacrylonitrile/Eu-pbmc membrane (PEM) by an in-situ growth strategy. Benefiting from the appreciable loading of Eu-pbmc nanoparticles and high water permeation flux, PEM possesses effective detection for MnO4− with a limit of detection (LOD) of 17 nM. Utilizing the cationic porous framework, we load MnO4− into PEM and construct a “on-off-on” system for effective AA detection. The oxidative MnO4− can be reduced by AA and the resulting turn-on luminescence can reflect the concentration of AA. Compared with pure Eu-pbmc crystals, PEM exhibits improved AA detection performance with LOD of 48 nM and detection time of 1 min via a concise detection operation. The stable membrane sensor realizes an accurate detection in real biological samples, meeting the practical requirement. Moreover, an IMP logic gate is helpful to analyze MnO4− and AA in water. The proposed novel luminescence platform as well as reasonable “on-off-on” luminescence mode provide a promising method for AA detection.

The mixed-valent tetramanganese MnIII3MnIV (Mn4) cubane clusters have been at the forefront of molecular magnetism and biomimetic catalysis research for decades. Incorporating robust polyoxometalates to Mn4 cubanes significantly improves their stability and aqueous solubility, while providing a great platform for studying their deposition onto selected surfaces during device fabrication. In this work, we discovered that the terminal carboxylate ligands in these polyoxometalate-based [MnIII3MnIVO4] magnetic clusters can be partially or completely replaced by inorganic phosphate/polyphosphate groups. This replacement leads to oligomeric aggregates of the Mn4 clusters. The magnetic data of the monomeric and oligomeric Mn4 clusters suggested that the introduction of inorganic phosphate bridges may not alter the S = 9/2 ground state of individual Mn4 clusters, although different magnetic behaviors, especially at low temperatures, were observed primarily because of intercluster interactions.

The rational development of an anion templation strategy for the construction of macrocycles has been historically limited to small anions, but large polyoxoanions can offer unmatched structural diversity and ample binding sites. Here we report the formation of a {Mo

A tritopic, Ni-substituted Keggin cluster, {SiW

Single-nanoparticle-level sensing allows us to measure individual molecular interactions and probe environmental stimuli at nanometer-scale resolution. Despite these premises, limited success has been met hitherto due to the demanding challenge to distinguish a dimmed signal from a noisy background. Here, we describe an approach for high-sensitivity single-nanoparticle-level sensing of divalent copper (Cu2+) ions through near-infrared-to-visible upconversion luminescence against a near-null background. This nanosensor utilizes ytterbium- (Yb3+) and erbium (Er3+)-doped sodium yttrium fluoride (NaYF4) upconversion nanoparticles (UCNPs) (maximal emission at 540 nm when excited at 980 nm) as an energy donor, of which the surface attaches Cu2+-dependent DNAzymes labeled with BHQ1 dye (Black Hole Quencher 1, maximal absorption at 548 nm) as energy acceptors. Adding a hint amount of Cu2+ ions resulted in the cleavage of a BHQ1-containing moiety in DNAzymes, thus turning on upconversion luminescence for sensitive detection. Indeed, this approach allows us to perform single-nanoparticle-level detection of Cu2+ ions with extraordinary signal-to-noise ratios (SNRs, >277) for all measured concentrations that cover 3 orders of magnitude (from sub-nM to μM). Importantly, a limit of detection of 220 pM was achieved, about sevenfold lower than the one at the ensemble level. Moreover, a stochastic particle-to-particle sensing behavior was also identified, featuring single-nanoparticle-level detection. This work untaps the usage of UCNPs for high-sensitivity single-nanoparticle-level biosensing.

Introducing functionalities into the interior of metal–organic cage complexes can confer properties and utilities (e.g. catalysis, separation, drug delivery, and guest recognition) that are distinct from those of unfunctionalized cages. Endohedral functionalization of such cage molecules, for decades, has largely relied on modifying their organic linkers to covalently append targeted functional groups to the interior surface. We herein introduce an effective coordination method to bring in functionalities at the metal sites instead, for a set of polyhedral cages where the nodes are in situ formed polyoxovanadate clusters, [VIV6O6(OCH3)9(μ6-SO4)(COO)3]2−. Replacing the central sulfates of these hexavanadate clusters with more strongly coordinating phosphonate groups allows the installation of functionalities within the cage cavities. Organophosphonates with phenyl, biphenyl, and terphenyl tails were examined for internalization. Depending on the size/shape of the cavities, small phosphonates can fit into the molecular containers whereas larger ones inhibit or transform the framework architecture, whereby the first non-cage complex was isolated from a reaction that otherwise would lead to entropically favored regular polyhedra cages. The results highlight the complex and dynamic nature of the self-assembly process involving polyoxometalates and the scope of molecular variety accessible by the introduction of endo functional groups., Installation of oversized functions within a metal–organic cage may “burst” or even transform the molecular cage itself.

The mixed-valent tetramanganese Mn

Developing portable membrane sensors to accurately detect the biomolecule ascorbic acid (AA) is extremely important for food safety and human health. Herein, we successfully design and synthesize a novel cationic metal organic framework (Eu-pbmc, Hpbmc = 2-(pyridine-2-yl)-1H-benzimidazole-5-carboxylic acid) and assemble polyacrylonitrile/Eu-pbmc membrane (PEM) by an in-situ growth strategy. Benefiting from the appreciable loading of Eu-pbmc nanoparticles and high water permeation flux, PEM possesses effective detection for MnO

Antibiotic contamination of water bodies is a major environmental concern. Exposure to superfluous antibiotics is an ecological stressor correlated to the development of antibiotic resistance. Thus, it is imperative that effective methods are developed to simultaneously detect and remove such antibiotics so as to avoid inadvertent release. Herein, two flexible three-dimensional (3D) zinc-based metal-organic frameworks (MOFs) {[Zn2(bcob)(OH)(H2O)]·DMA}n (ROD-Zn1) and {[Zn(Hbcob)]·(solvent)}n (ROD-Zn2) (H3bcob = 1,3-bis((4'-carboxylbenzyl)oxy)benzoic acid) with rod second building units (SBUs) are successfully prepared. Their exceptional water and chemical stabilities (toward both acid and base), fast sorption kinetics, and unique framework endow the MOFs with excellent uptake capacity toward various antibiotics in the aqueous environment. The adsorption performance was further optimized by one-pot preparation of MOF-melamine foam (MF) hybrid composites, resulting in a hierarchical microporous-macroporous MOF@MF system (ROD-Zn1@MF and ROD-Zn2@MF), which are readily recyclable after adsorptive capture. The mechanisms of adsorption have been deeply investigated by static and competitive adsorption experiments. In addition, the MOFs exhibit excellent fluorescent properties and quenched by trace amounts of antibiotics in water solution. Therefore, ROD-Zn1 and ROD-Zn2 present a dual-functional performance, being promising candidates for detection and removal of antibiotics.

Altering the organic spacers in hybrid complexes of polyoxotungstates and long-chain α,ω-alkyldiphosphonates (Ln), by a single CH2 group (e.g.L6vs.L5), can steer the self-assembly processes into different paths. Even homologous hybrids of L5 and L4 have seen the spin ground states switch from S = 0 to S = 9 upon shortening the chain length (L5vs.L4).

A pair of redox flow batteries containing polyoxometalates was tested as part of an ongoing program in stationary energy storage. The iron-containing dimer, (SiFe3W9(OH)3O34)2(OH)311−, cycled between (SiFe3W9(OH)3O34)2(OH)311−/(SiFe3W9(OH)3O34)2(OH)314−and (SiFe3W9(OH)3O34)2(OH)317−/(SiFe3W9(OH)3O34)2(OH)314− for the positive and negative electrode, respectively. This compound demonstrated a coulombic efficiency of 83% after 20 cycles with an electrochemical yield (measured discharge capacity as a percentage of theoretical capacity) of 55%. Cyclic voltammetry on the Lindqvist ion, cis-V2W4O194−, showed quasi-reversible vanadium electrochemistry, but tungsten reduction was mostly irreversible. In a flow cell configuration, cis-V2W4O194−had a coulombic efficiency of 45% (for a two-electron process) and an electrochemical yield of 16% after 20 cycles. The poor performance of cis-V2W4O194−was attributed primarily to its higher charge density. Collectively, the results showed that both polyoxometalate size and charge density are both important parameters to consider in battery material performance.

Flow batteries including an electrolyte of a polyoxometalate material are disclosed herein. In a general embodiment, the flow battery includes an electrochemical cell including an anode portion, a cathode portion and a separator disposed between the anode portion and the cathode portion. Each of the anode portion and the cathode portion comprises a polyoxometalate material. The flow battery further includes an anode electrode disposed in the anode portion and a cathode electrode disposed in the cathode portion.

Polynuclear open-shell transition-metal clusters are synthetically challenging, yet fascinating from the perspective of their diverse properties. Iron clusters in particular can exhibit interesting magnetic and electrochemical behaviour, and they can potentially be exploited as models for geochemical processes at iron oxide surfaces. From solvothermal synthesis, we have obtained a cagelike polycationic FeIII cluster, [Fe15Cl6O6(OH)2(C3H6O2)12]+, which features the common polyoxometalate (POM) Keggin ion trimer fragments oriented in an inverse fashion relative to the centre of the cluster. In addition to solid-state structural characterization, we have examined the magnetic properties, which revealed the presence of antiferromagnetic exchange within the polynuclear system. Electrospray-ionization mass spectrometry (ESI-MS) revealed that the Fe9 core of the cluster remains intact upon dissolution, whereas the Fe–Cl2+ caps are more labile. Computational studies agree well with the observed antiferromagnetic character, as well as the HOMO–LUMO bandgap, and also describe these frontier orbitals.

The biomimetic synthesis of fused bispyran via Lewis acid mediated tandem oxacyclization of a 1,4,7-polyepoxide is explored. The nature of the Lewis acid promoter is critical for the endo-regioselectivity of epoxide cyclization, although anomalous apparent retention of stereochemistry is observed at some reactive centers.

Lanthanide complexes of polyoxometalates, including the α2-P2W17O61 10− ligand, have been pioneered by Michael T. Pope, to whom this paper is dedicated. Examination of the solid-state and solution behavior of lanthanide complexes of the α2-P2W17O61 10− ligand are reported here to identify trends that will facilitate rational synthesis of hybrid organic lanthanide polyoxometalate complexes. Therefore, combining our data with that obtained by Pope and others a number of trends come into view. It is clear that there are two structural types for the 1:1 or 2:2 [Ln(H2O)X(α2-P2W17O61)]2 14− species. The early lanthanides show a “cap to cap” structure that allows the Ln ion to be 9 coordinate and accommodates the longer bond lengths. The mid-late lanthanides show a “cap to belt” structure that allows the lanthanides to be 8 coordinate; this structural type is appropriate for the shorter bond lengths of the later lanthanides. The 1:1⇌1:2 equilibrium, that was observed by Pope for the Ce(III) analog is prevalent for the early- mid lanthanides. This equilibrium is slightly dependent on pH; however, cations have a major influence on this equilibrium. Larger, poorly hydrated cations appear to favor the 1:2 species for the early to mid lanthanides. Cations do not appear to influence the equilibrium for the later lanthanides; for all counterions, the 1:1 species was stable with no trace of the 1:2 species. Stability constants, K1 and K2, for the early to mid lanthanides were measured in this study by a competitive method and compared well with other published stability constant determinations. We suggest that the stability constants are not only dependent on the strength of interaction of the Ln with the α2-P2W17O61 10− ligand, but are also significantly influenced by the medium. The medium may bias the equilibria of the early-mid lanthanides and later lanthanides. The log K1/log K2 ratios are very close, suggesting that it is difficult to separate the 1:1 and 1:2 Ln: α2-P2W17O61 10− species.

A new Wells–Dawson sandwich polyoxometalate, $$\alpha\alpha\alpha\alpha$$ -[(NaOH2)2(CuII)2 (P2W15O56)2]18− (2P), has been obtained in good yield by the dissolution of solid $$\alpha$$ -Na12[P2W15O56]·18H2O in an aqueous solution of Cu(II) and L-glutamic acid at pH 10. The arsenic analogue, $$\alpha\alpha\alpha\alpha$$ -[(NaOH2)2(CuII)2(As2W15O56)2]18− (2As), is likewise prepared by using Na12[As2W15O56]·21H2O instead of Na12[P2W15O56]·18H2O. Diffraction quality crystals of both 2P and 2As were obtained by slow evaporation in air over several days. The X-ray structures of 2P and 2As reveal that two Cu(II) atoms are sandwiched between two $$\alpha$$ -[P2W15O56]12− or two $$\alpha$$ -[As2W15O56]12− ligands, respectively, while the other two positions of the central belt unit are occupied by two Na+ cations. Higher yields of 2As can be obtained by mixing CuCl2·2H2O and $$\alpha$$ [Na12As2W15O56]·21H2O in acetate buffer. The electrochemistry of 2P and 2As is characterized by cyclic voltammograms in which the reduction of the Cu(II) centers is close to the redox pattern of the W-centers. The two Cu(II)-centers are simultaneously reduced to Cu(0); the separate steps could not be resolved for the individual Cu(II) centers. Complexes 2P and 2As constitute the second example, after $$\alpha\alpha\alpha\alpha$$ -[(NaOH2)2(FeIII)2(P2W15O56)2]16− (1P) and $$\alpha\alpha\alpha\alpha$$ -[(NaOH2)2(FeIII)2(As2W15O56)2]16− (1As), of a transition-metal-substituted sandwich polyoxometalate containing two electroactive d-electron metals.

A macroion, having anisotropic surface charge density distribution, shows unique self-assembly behaviour in polar solvents. Regular "blackberry"-like assemblies form in methanol-water mixtures due to counter-ion mediated attraction and the strong contribution of hydrogen bonding. However, rod-like assemblies form in acetone-water mixtures as the charge inhomogeneity effect overcomes the non-directional hydrogen bonding.

The colorless crystals of the novel dimeric polyoxometalate Na 12 H 4 [A-β-PW 9 O 34 Na(H 2 O)] 2 ·38H 2 O were obtained by recrystallization of the precursor Na 9 [A-PW 9 O 34 ]·19H 2 O in acidic solution. The crystal is triclinic, space group P 1 , with lattice constants a=12.6134(4) A , b=13.146(6) A , c=18.243(4) A , α =88.373(3)°, β =69.92(2)°, γ =63.23(3)°, V=2507.4(14) A 3 and Z =1. The crystal structure confirms the dimeric anhydride is formed by Na–O–Na bridges linking two A-β-PW 9 O 34 Keggin units. One of the Na + ions is linked with the inner oxygen atom [O a (1)] forming a dimeric anion, while the coordination of polyoxoanions with Na + ions and water molecules results in a two-dimension network structure.

POM and circumstance: Nanometer-sized polyoxometalates (POMs) bring a new direction to anion-templated supramolecular chemistry. The Keggin (left) and Dawson-type (right) polyoxoanions direct the assembly of giant metallomacrocycles through an array of weak hydrogen-bonding interactions. The concerted action of multiple hydrogen bonds keeps the templating guests embedded within the hosts, even in the solution state.

A polyoxometalate-based {Mn(III)(3)Mn(IV)} single-molecule magnet exhibits a large axial anisotropy (D = -0.86 cm(-1)) resulting from a near-parallel alignment of Jahn-Teller axes. Its rigorous three-fold symmetry (i.e. rhombicity E→ 0) and increased intercluster separation via co-crystallization effectively hamper quantum tunnelling of the magnetization.

Ligand modification transforms a polyoxometalate-anchored cubane-type [Mn(III)(3)Mn(IV)O(4)] core into a centrosymmetric [Mn(III)(6)Mn(IV)O(8)] di-cubane cluster, and restores the slow magnetization relaxation characteristics typical for [Mn(4)O(4)] cubane-based single-molecule magnets.

The functionalization of a pre-formed, high oxidation state {CeIV MnIV 6} cluster with a lacunary phosphotungstate, [alpha-P2 W15 O 56]12-, exemplifies a straightforward route for grafting redox-active building blocks to existing Mn-carboxylate clusters and modeling their deposition onto metal oxide surfaces.

Our measurements of the differential susceptibility $\ensuremath{\partial}M/\ensuremath{\partial}H$ of the frustrated magnetic molecules ${{\text{Mo}}_{72}{\text{Fe}}_{30}}$ and ${{\text{Mo}}_{72}{\text{Cr}}_{30}}$ reveal a pronounced dependence on magnetic field $(H)$ and temperature $(T)$ in the low $H$--low $T$ regime, contrary to the predictions of the existing models. Excellent agreement with experiment is achieved upon formulating a nearest-neighbor classical Heisenberg model where the 60 nearest-neighbor exchange interactions in each molecule, rather than being identical as has been assumed heretofore, are described by a two-parameter rectangular probability distribution of values of the exchange constant. We suggest that the probability distribution provides a convenient phenomenological platform for summarizing the combined effects of multiple microscopic mechanisms that disrupt the idealized picture of a Heisenberg model based on a single value of the nearest-neighbor exchange constant.

The boronic acid functional group plays very important roles in sugar recognition, catalysis, organic synthesis, and supramolecular assembly. Therefore, understanding the unique properties of this functional group is very important. 8-Quinolineboronic acid (8-QBA) is found to be capable of self-assembling in solid state through a unique intermolecular B-N bond mechanism reinforced by intermolecular boronic anhydride formation, π-π stacking, and hydrogen bond formation. NMR NOE and diffusion studies indicate that intermolecular B-N interaction also exists in solution with 8-QBA. In contrast, a positional isomer of 8-QBA, 5-quinolineboronic acid (5-QBA) showed very different behaviors in crystal packing and in solution and therefore different supramolecular network. Understanding the structural features of this unique 8-QBA assembly could be very helpful for the future design of new sugar sensors, molecular catalysts, and supramolecular assemblies.

A chiral polyoxometalate [Hf(PW11O39)2]10- (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P2(1)2(1)2, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39]7- units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate HfIV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantiomers were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems.

The bulk magnetization at temperatures of $1.8--400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and in magnetic fields up to $70\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, the ambient temperature $^{13}\mathrm{C}$ NMR spin-lattice relaxation, ${T}_{1,C}$, and the elemental composition of three nanodiamond powder samples have been studied. The total magnetization of nanodiamond can be explained in terms of contributions from (1) the diamagnetic effect of carbon, (2) the paramagnetic effect of unpaired electrons present in nanodiamond grains, and (3) ferromagneticlike and (4) superparamagnetic contributions from Fe-containing particles detected in spatially resolved energy-dispersive spectroscopy. Contributions (1) and (2) are intrinsic to nanodiamond, while contributions (3) and (4) arise from impurities naturally present in detonation nanodiamond samples. $^{13}\mathrm{C}$ NMR ${T}_{1,C}$ relaxation would be unaffected by the presence of the ferromagnetic particles with the bulk magnetization of $\ensuremath{\sim}0.01\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕\mathrm{g}$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Thus, a reduction of ${T}_{1,C}$ by 3 orders of magnitude compared to natural and synthetic microdiamonds confirms the presence of unpaired electrons in the nanodiamond grains. The spin concentration in nanodiamond powder corresponds to $\ensuremath{\sim}30$ unpaired electrons per $\ensuremath{\sim}4.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ diameter nanodiamond grain.

A chiral polyoxometalate [Hf(PW11O39)2]10- (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P2(1)2(1)2, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39]7- units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate HfIV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantiomers were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems.

In contradiction to current bonding paradigms, two terminal Au-oxo molecular complexes have been synthesized by reaction of AuCl3 with metal oxide-cluster ligands that model redox-active metal oxide surfaces. Use of K10[alpha2-P2W17O61].20H2O and K2WO4 (forming the [A-PW9O34]9- ligand in situ) produces K15H2[Au(O)(OH2)P2W18O68].25H2O (1); use of K10[P2W20O70(OH2)2].22H2O (3) produces K7H2[Au(O)(OH2)P2W20O70(OH2)2].27H2O (2). Complex 1 crystallizes in orthorhombic Fddd, with a=28.594(4) A, b=31.866(4) A, c=38.241(5) A, V=34844(7) A3, Z=16 (final R=0.0540), and complex 2 crystallizes in hexagonal P6(3)/mmc, with a=16.1730(9) A, b=16.1730(9) A, c=19.7659(15) A, V=4477.4(5) A3, Z=2 (final R=0.0634). The polyanion unit in 1 is disorder-free. Very short (approximately 1.76 A) Au-oxo distances are established by both X-ray and 30 K neutron diffraction studies, and the latter confirms oxo and trans aqua (H2O) ligands on Au. Seven findings clarify that Au and not W is present in the Au-oxo position in 1 and 2. Five lines of evidence are consistent with the presence of d8 Au(III) centers that are stabilized by the flanking polytungstate ligands in both 1 and 2: redox titrations, electrochemical measurements, 17 K optical spectra, Au L2 edge X-ray absorption spectroscopy, and Au-oxo bond distances. Variable-temperature magnetic susceptibility data for crystalline 1 and 2 establish that both solids are diamagnetic, and 31P and 17O NMR spectroscopy confirm that both remain diamagnetic in solution. Both complexes have been further characterized by FT-IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and other techniques.