Structure, Magnetism, and Ionic Conductivity of the Gigantic {Mo176}-Wheel Assembly: Na15Fe3Co16[Mo176O528H3(H2O)80]Cl27·450H2O

Insights into the self-assembly of giant polyoxomolybdates from building blocks to supramolecular structures

Giant polyoxomolybdates are a special class of polyoxometalate clusters which can bridge the gap between small molecule clusters and large polymeric entities. Besides, giant polyoxomolybdates also show interesting applications in catalysis, biochemistry, photovoltaic and electronic devices, and other fields. Revealing the evolution route of the reducing species into the final cluster structure and also their further hierarchical self-assembly behaviour is undoubtedly fascinating, aiming to guide the design and synthesis. Herein, we reviewed the self-assembly mechanism study of giant polyoxomolybdate clusters, and the exploration of a new structure and new synthesis methodology is also summarized. Finally, we emphasize the importance of in-operando characterization in revealing the self-assembly mechanism of giant polyoxomolybdates, and especially for the further reconstruction of intermediates into the designable synthesis of new structures.

Accurate binding of porous aluminum molecular ring catalysts with the substrate

Metal molecular rings are a class of compounds with aesthetically pleasing symmetry and fundamentally useful properties. The reported work generally focuses on the ring center cavity, and there is little known about those on the ring waist. Herein, we report the discovery of porous aluminum molecular rings and their performance and contribution to the cyanosilylation reaction. We develop a facile ligand induced aggregation and solvent regulation strategy towards AlOC-58NC and AlOC-59NT with high purity, high yield (75% and 70%, respectively) and gram-level scale-up. These molecular rings exhibit a "two-tier" pore feature involving the general central cavity and newly observed equatorial semi-open cavities. AlOC-59NT with two types of one-dimensional channels showed good catalytic activity. The interaction of the aluminum molecular ring catalyst with the substrate has been crystallographically characterized and theoretically confirmed, showing a ring adaptability process that involves the capture and binding of the substrate. This work provides new ideas for the assembly of porous metal molecular rings and to understand the overall reaction pathway involving aldehydes and is expected to inspire the design of low-cost catalysts through structural modifications.

Gradual Size Enlargement of Aluminum-Oxo Clusters and the Photochromic Properties

Metallic clusters, assembled by functional motifs, possess the attribute of regulating the properties by changing inorganic and organic components. In this work, a series of aluminum-oxo clusters, [Al₆O(dmp)₄(Hdmp)₂]·2ⁱPrOH [Al₆-1, H₃dmp = 2,2-bis(hydroxymethyl)propionic acid], [Al₆(H₂thmmg)₆]·2DMF·2H₂O [Al₆-2, H₅thmmg = N-tris(hydroxymethyl)methylglycine], [Al₈(OH)₄(NAP-OH)₁₂(MeO)₇(MeOH)]Cl·7MeCN·3MeOH (Al₈, HNAP-OH = 3-hydroxy-2-naphthoic acid), and [Al₁₀(NA)₁₀(MeO)₂₀] (Al₁₀, HNA = nicotinic acid), were obtained based on different carboxylic acids, realizing metallic ring size enlargement from 5.91 to 9.32 Å. They all exhibit good chemical stability. Importantly, the Al₈ cluster displays obvious photochromic behavior from pale yellow to orange yellow, originating from the generation of photoinduced radicals in the metal-assisted ligand-ligand electron transfer process of 3-hydroxy-2-naphthoic acid (HNAP-OH). This work enriches the metal ring cluster chemistry and reports the example of the aluminum-oxo cluster-based photochromic material, developing a novel system of photochromic materials.

Third-order optical nonlinearities of zinc porphyrins accommodated in the cavity of a doughnut-like molybdenum crown cluster

In this paper, three zinc porphyrins bearing carboxyl, amino or hydroxyl groups on the porphyrin ring, namely, 5,10,15,20-tetra(4-carboxyphenyl) zinc porphyrin (ZnTCPP), 5,10,15,20-tetra(4-hydroxyphenyl) zinc porphyrin (ZnTHPP) and 5,10,15,20-tetra(4-aminophenyl) zinc porphyrin (ZnTAPP), reacted with the doughnut-like molybdenum crown cluster [(MoO₃)₁₇₆(H₂O)₆₃(CH₃OH)₁₇H₁₆]^16- (denoted as {Mo₁₇₆}), resulting in the formation of three porphyrin-polyoxometalate hybrids (denoted as hybrids 1-3), respectively, with the ratio of {Mo₁₇₆} to the porphyrin molecules in each compound being 1 : 3. Compared with the corresponding parent porphyrins, the fluorescence quenching efficiency of hybrid 1, hybrid 2 and hybrid 3 was found to be 51%, 58% and 66%, respectively, indicating electron/energy transfer occurring from the porphyrin moiety to the POM moiety. Z-Scan experimental results showed that the three porphyrins and hybrids 1-3 exhibited nonlinear reverse saturated absorption and self-defocusing properties. The molecular second hyperpolarizability (γ) values of hybrids 1-3 (7.38 × 10^-27, 7.26 × 10^-27 and 4.26 × 10^-27 (esu)) are higher than those of the corresponding porphyrins (1.18 × 10^-27, 1.34 × 10^-27 and 1.36 × 10^-27 (esu)), indicating that the doughnut-like molybdenum crown cluster in the hybrids 1-3 improved the third-order optical nonlinearities of the accommodated H-aggregate of the zinc porphyrin molecules, wherein the optical nonlinearities of the porphyrin with the electron-withdrawing functional group of -COOH (γ = 7.38 × 10^-27 for hybrid 1vs. γ = 1.18 × 10^-27 for ZnTCPP) were enhanced the most. In addition, studies on the optical limiting properties of hybrid 1 and hybrid 2 showed that the nonlinear attenuation factor (NAF) of both hybrid 1 and hybrid 2 was larger than that of their corresponding porphyrins (NAF = 5.65 for hybrid 1vs. 1.82 for ZnTCPP) and the limiting threshold of hybrid 1 and hybrid 2 can reach 0.3 J cm^-2 and 0.32 J cm^-2, which proved that hybrids 1 and 2 are potential optical limiting materials.

Comment on molybdenum polyoxo clusters: from the `Blues' to the `Reds'

Molybdenum ‘Blues’, ‘Browns’ and the recently discovered ‘Reds’ are unquestionably some of the most impressive nanoscale architectures in POM chemistry. In this context, Al-Sayed et al. (2022) recently made a significant contribution, reporting a new binding mode of an organic hybridization reagent in mixed-valence polyoxomolybdates.

Aluminum molecular rings bearing amino-polyalcohol for iodine capture

Amino-polyalcohol-solvothermal synthesis leads to the isolation of a broad range of aluminum molecular rings, which exhibit considerable affinity towards iodine molecules.

Macrocyclic Inorganic Tin-Containing Oxo Clusters: Heterometallic Strategy for Configuration and Catalytic Activity Modulation

In this work, the first examples of inorganic macrocyclic tin-oxo clusters which are stabilized by sulfate ligands are reported. As determined by X-ray diffraction and photoelectron spectroscopy analyses, the prepared inorganic Sn₁₀ -oxo cluster displays interesting mixed valence behaviors, with 8 Sn⁴⁺ located at the cyclic skeleton and two Sn²⁺ encapsulated in the center. When further introducing Ti⁴⁺ and In³⁺ ions to the synthetic systems, heterometallic Sn₂ Ti₆ and SnIn₅ Ti₆ complexes with Ti₆ (SO₄ )₉ and SnIn₅ (SO₄ )₁₂ macrocyclic skeletons were prepared whose configuration and packing models were affected by the ionic radius of incorporated metals. Moreover, comparative CO₂ reduction experiments confirm that such heterometallic composition can significantly improve the catalytic activities of these inorganic macrocyclic oxo clusters. This work represents a milestone in constructing inorganic tin complexes and also macrocyclic metal oxo clusters with tunable configurations and properties.

A new ZnII coordination polymer based on 4-(pyridin-4-yl)benzoic and formic acids: in-situ synthesis, crystal structure and luminescence properties

The title compound, poly[(μ2-formato-κ3 O,O′:O)[μ2-4-(pyridin-4-yl)benzoato-κ3 N:O,O′]zinc(II)], [Zn(C12H8NO2)(HCOO)] n , has been synthesized in situ and characterized by thermogravimetric analysis (TGA) and single-crystal and powder X-ray diffraction analyses. The polymer contains two independent structural units in the asymmetric unit. These are constructed from Zn2+ ions, 4-(pyridin-4-yl)benzoate (4-pbc) bridges and in-situ-generated formate ligands, forming two similar two-dimensional (2D) layer structures. These similar 2D layers are arranged alternately and are linked with each other by dense C—H...O hydrogen bonds to generate a three-dimensional (3D) supramolecular framework. The crystal is pseudomerohedrally twinned about [201]. Compared with free 4-Hpbc, the polymer exhibits a red shift and significantly enhanced solid-state luminescence properties.

Homochiral hexanuclear nickel(ii) metallocyclic structures with high activity for the photocatalytic degradation of organic dyes

Two chiral hexanuclear nickel(ii) metallocyclic rings with new chiral ligands exhibit excellent activity for the photocatalytic degradation of organic dyes.

pH-Controlled assembly of two novel Dawson-sandwiched clusters involving the in situ reorganization of trivacant α-[P2W15O56](12-) into divacant α-[P2W16O57](8.)

Modified classical trivacant Wells-Dawson α-[P2W15O56](12-) and the assembly of related sandwiched transition metal clusters are of interest, but surprisingly few reports of these materials exist because of the sensitivity of α-[P2W15O56](12-) to the assembly environment. Herein, we describe the pH-controlled assembly of two novel Dawson-sandwiched clusters, (H2bpz)6[Co2(P2W16O57)2]·22H2O (1, bpz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole) and (H2bpz)6[Co3H2(P2W16O57)(P2W15O56)(H2O)]·12H2O (2), involving the in situ transformation of α-[P2W15O56](12-). Both clusters were characterized by X-ray single-crystal diffraction, FT-IR spectroscopy, UV-Visible spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and elemental analyses. X-ray crystallography showed that both heteropolytungstates become divacant α-[P2W16O57](8-) and symmetrically encapsulate two edge-shared CoO6 octahedra in the interior in 1, while only one divacant α-[P2W16O57](8-) is observed in 2, which combined with another trivacant α-[P2W15O56](12-) to asymmetrically clamp three edge-shared CoO6 octahedra. The α-[P2W16O57](8-) heteropolytungstate should be generated in situ from α-[P2W15O56](12-)via self-decomposition equilibria in solution. Their electrochemical behaviors reveal characteristic multi-electron redox processes related to W(VI) centers. The electrocatalytic reduction performances toward nitrite, hydrogen peroxide, chlorate, bromate and iodate were fully measured and discussed; among these species, both clusters exhibit the best electrocatalytic activity towards the reduction of bromate. Magnetic measurements indicate weak ferromagnetic exchange interactions between Co atoms sandwiched by vacant polyoxometalates.

Rearrangement of {α-P2W15} to {PW6} moieties during the assembly of transition-metal-linked polyoxometalate clusters

Formation of a series of polyoxometalates showing the unprecedented transformation of a Dawson lacunae into a Keggin lacunae.

Synthesis and characterization of [(HPO3)6Mo21O60(H2O)4]8−: a new redox active heteropoly blue cluster with layered shape containing a phosphite template that self-assembles under controlled microwave irradiation

A redox active layered shape [(HPO₃)₆Mo₂₁O₆₀(H₂O)₄]⁸⁻ with a phosphite template is synthesised by a microwave-assisted method and characterized.

A single-stranded {Gd18} nanowheel with a symmetric polydentate diacylhydrazone ligand

A {Gd₁₈} nanowheel was solvothermally synthesized. It features a rare single-stranded skeleton that looks like a Reuleaux triangle with vertices buckled in, represents the highest nuclearity and the largest size in any pure Ln wheels reported, and shows a large MCE.

Investigating the formation of "molybdenum blues" with gel electrophoresis and mass spectrometry

The reduction of solutions of acidified molybdate leads to the formation of a family of nanostructured molybdenum blue (MB) wheels which are linked together in a series of complex reaction networks. These networks are complex because the species which define the nodes are extremely labile, unstable, and common to many different networks. Herein, we combine gel electrophoresis and electrospray ionization mass spectrometry (ESI-MS) to investigate the effect of the pH and the ratio of reactants and reducing agents, R (R = [S2O4(2-)]/[MoO4(2-)]), on the complex underlying set of equilibria that make up MBs. By mapping the reaction parameter space given by experimental variables such as pH, R, solvent medium, and type of counterion, we show that the species present range from nanostructured MB wheels (comprising ca. 154 Mo atoms) to smaller molecular capsules, [(SO3)2Mo(V)2Mo(VI)16O54](6-) ({S2Mo18}), and templated hexameric [(μ6-SO3)Mo(V)6O15(μ2-SO3)3](8-)({S4Mo6}) anions. The parallel effects of templation and reduction on the self-assembly process are discussed, taking into consideration the Lewis basicity of the template, the oxidation state of the Mo centers, and the polarity of the reaction medium. Finally, we report a new type of molecular cage (TBA)5[Na(SO3)2(PhPO3)4Mo(V)4Mo(VI)14O49]·nMeCN (1), templated by SO3(2-) anions and decorated by organic ligands. This discovery results from the exploration of the cooperative effect of two anions possessing comparable Lewis basicity, and we believe this constitutes a new synthetic approach for the design of new nanostructured molecular metal oxides and will lead to a greater understanding of the complex reaction networks underpinning the assembly of this family of nanoclusters.

A nano-scale triangular ring cluster of indium–selenide: the structure and templating effect

The preparation and crystal structure of a novel nano-scale triangular In₃₃Se₆₀ ring cluster are reported. An inverse second-sphere coordination templating effect is responsible for the formation of the unusual triangular ring. The optical and electronic properties of the nanoring cluster are discussed.

The chloridomolybdenum(III) cluster in [BMIm]4[AgMo10Cl35] with infinite chains of Ag(+)-linked [Mo10Cl35](5-) wheels

[BMIm]4[AgMo10Cl35] is prepared by reaction of MoCl5 and elemental silver in the ionic liquid [BMIm][AlCl4] ([BMIm(+)]: 1-butyl-4-methylimidazolium). Surprisingly, elemental silver is oxidized under these conditions. The title compound contains a new wheel-shaped [Mo10Cl35](5-) chlorido molybdenum(iii) species with five pairs of Mo-Mo bonds. The Mo-Mo distances are found to be 263 pm on average. The [Mo10Cl35](5-) wheels exhibit a maximum opening of 558 pm in diameter. They are interlinked via Ag(+) to form infinite [AgMo10Cl35](4-) chains. The title compound is characterized by single crystal structure analysis, EDX, FT-IR and UV-Vis spectroscopy. The wheel-type structure and Ag(+) linkage to infinite chains are a new aspect of halogenido metalates and low-valence molybdenum compounds.

A twofold interwoven two-dimensional→two-dimensional (2-D→2-D) cluster-organic network based on the [Cu2I2] cluster and the 4,4'-(diazenediyl)dipyridine ligand: poly[[μ2-4,4'-(diazenediyl)dipyridine]-μ2-iodido-copper(I)]

In the polymeric title compound, [CuI(C(10)H(8)N(4))](n), the Cu(I) atom is in a four-coordinated tetrahedral geometry, formed by two I atoms and two pyridine N atoms from two different 4,4'-(diazenediyl)dipyridine (4,4'-azpy) ligands. Two μ(2)-I atoms link two Cu(I) atoms to form a planar rhomboid [Cu(2)I(2)] cluster located on an inversion centre, where the distance between two Cu(I) atoms is 2.7781 (15) Å and the Cu-I bond lengths are 2.6290 (13) and 2.7495 (15) Å. The bridging 4,4'-azpy ligands connect the [Cu(2)I(2)] clusters into a two-dimensional (2-D) double-layered grid-like network [parallel to the (10-2) plane], with a (4,4)-connected topology. Two 2-D grid-like networks interweave each other by long 4,4'-azpy bridging ligands to form a dense 2-D double-layered network. To the best of our knowledge, this interwoven 2-D→2-D network is observed for the first time in [Cu(2)I(2)]-organic compounds.