Advances in Understanding the Electrocatalytic Reconstruction Chemistry of Coordination Compounds

Coordination compounds including mainstream metal-organic frameworks and Prussian blue analogues receive extensive researches when they directly serve as electrocatalysts. Their reconstruction phenomena, that are closely associated with actual contributions and intrinsic catalytic mechanisms, are expected to be well summarized. Here, the recent advances in understanding reconstruction chemistry of coordination compounds are reviewed, including their main classifications and structural properties, reconstruction phenomena in electrocatalysis (e.g., oxygen/hydrogen evolution reaction, CO₂ reduction), influence factors of reconstruction parameters (e.g., reconstruction rate and reconstruction degree), and reconstruction-performance correlation. It is outlined that the reconstruction processes are influenced by electronic structure of coordination compounds, pH and temperature of testing solution, and applied potentials. The characterization techniques reflecting the evolution information before and after catalysis are also introduced for reconstruction-related mechanistic study. Finally, some challenges and outlooks on reconstruction investigations of coordination compounds are proposed, and the necessity of studying and understanding of these themes under actual working conditions of devices is highlighted.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

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

Ln(iii)-Containing polyoxomolybdates based on β-{Mo8O28}: microwave synthesis and optical and magnetic properties

The reactant mother liquor can be obtained by 600 watt microwave irradiation for 15 minutes. Under ultraviolet irradiation, these two compounds can undergo the photochromic process, and the fading process can occur after the ultraviolet irradiation was turned off.

Toward Exploiting the Behavior of Niobium-Containing Mesoporous Silicates vs. Polyoxometalates in Catalysis

Classification of polyoxometalates (POMs) is based on their chemical composition, basically represented by two general formulae: a) [MmOy]p- b) [XxMmOy]q-, where M is the main transition metal, O is the oxygen atom and X can be a non-metal atom such as Si. Additionally, in the most cases, the structure of the polyoxometalates is derived from a combination of octahedral units MO6 with a central metal atom M and the oxygen atoms placed at their corners. In such octahedra, oxygen atoms allow the condensation between two octahedral units, while one oxygen atom (or max. two atoms) makes double bond with the central metal atom and is not shared with other metal atoms within the complex (terminal oxygens). On the other hand, niobium-containing mesoporous silicates contain mainly MO4 tetrahedra and reveal superior activity in heterogeneous catalysis. Thus, the proper coordination of niobium is crucial for the catalytic activity and will be deeply discussed. The similarity in the catalytic behavior of niobium-polyoxometalates and heterogeneous niobium single-site catalysts in selective oxidations will be demonstrated.

On the Border between Low-Nuclearity and One-Dimensional Solids: A Unique Interplay of 1,2,4-Triazolyl-Based {CuII5(OH)2} Clusters and MoVI-Oxide Matrix

A pentanuclear Cu^II₅-hydroxo cluster possessing an unusual linear-shaped configuration was formed and crystallized under hydrothermal conditions as a result of the unique cooperation of bridging 1,2,4-triazole ligand ( trans-1,4-cyclohexanediyl-4,4'-bi(1,2,4-triazole) ( tr₂ cy)), Mo^VI-oxide, and CuSO₄. This structural motif can be rationalized by assuming in situ generation of {Cu₂Mo₆O₂₂}^4- anions, which represent heteroleptic derivatives of γ-type [Mo₈O₂₆]^4- further interlinked by [Cu₃(OH)₂]⁴⁺ cations through [ N- N] bridges. The framework structure of the resulting compound [Cu₅(OH)₂( tr₂ cy)₂Mo₆O₂₂]·6H₂O (1) is thus built up from neutral heterometallic {Cu₅(OH)₂Mo₆O₂₂} _n layers pillared with tetradentate tr₂ cy. Quantum-chemical calculations demonstrate that the exclusive site of the parent γ-[Mo₈O₂₆]^4- cluster into which Cu^II inserts corresponds with the site that has the lowest defect ("MoO₂ vacancy") formation energy, demonstrating how the local metal-polyoxomolybdate chemistry can express itself in the final crystal structure. Magnetic susceptibility measurements of 1 show strong antiferromagnetic coupling within the Cu₅ chain with exchange parameters J₁ = -500(40) K (-348(28) cm^-1), J₂ = -350(10) K (-243(7) cm^-1) and g = 2.32(2), χ² = 6.5 × 10^-4. Periodic quantum-chemical calculations reproduce the antiferromagnetic character of 1 and connect it with an effective ligand-mediated spin coupling mechanism that comes about from the favorable structural arrangement between the Cu centers and the OH^-, O^2-, and tr₂ cy bridging ligands.

Two new molybdates based on ∞[MonO3n+1]2− units (n = 11, 4) with proton conduction under ionothermal

Two new members of the _∞[Mo_nO_3n+1]²⁻ family with high proton conduction synthesized under ionothermal condition.

Norfloxacin-derivative functionalized octamolybdate: unusual carbonyl coordination and acidity sensitive luminescence

The first γ-type octamolybdate functionalized by decarboxylated norfloxacin, (dNF)₂[γ-Mo₈O₂₆(dNF)₂]·10H₂O, has been synthesized featuring unusual carbonyl coordination. The fluorescence is sensitive to acidity and can be used as an acid–base switch.

Metal-organic frameworks based on the [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid ligand: syntheses, structures and magnetic properties

The solvothermal reactions of [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTA) with transition metal cations afforded five novel coordination polymers in the presence of three pyridine ligands (4,4'-bipy = 4,4'-bipyridine, 2,2'-bipy = 2,2'-bipyridine and phen = 1,10-phenanthroline), namely [M(TPTA)0.5(4,4'-bpy)0.5(H2O)2]n (M = Co for (1), Ni for (2)), {[Mn2(TPTA)(2,2'-bpy)H2O]·1.5H2O}n (3), and [M(H2TPTA)(phen)]n (M = Mn for (4), Co for (5)). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Polymers 1 and 2 are isomorphous and exhibit 3D 4-fold interpenetrated networks with the point Schläfli symbol of (4(2)·10(4)) (4·10(2)). Polymer 3 shows a 2D layer framework. Polymers 4 and 5 are also isomorphous and each displays a one-dimensional (1D) chain, which further forms a 2D supramolecular architecture via inter-chain π···π interactions. Moreover, variable-temperature magnetic susceptibilities of polymers 3-5 exhibit overall weak antiferromagnetic coupling between the adjacent M(II) ions.

Photoluminescent 3D lanthanide MOFs with a rare (10,3)-d net based on a new tripodal organic linker

Isomorphous Ln-MOFs with a rare (10,3)-d network were assembled from a dual functional ligand which sensitizes Ln-based luminescence, achieving high quantum yield for Tb-MOF.

Isopolymolybdate-induced organic–inorganic hybrid assemblies with copper ions and bichelate-bridging ligands

Heptamolybdate is used as a “molecular adaptor” to modulate the metal–organic coordination building units in the hydrothermal environment, with new polyoxometalate-induced hybrid assemblies isolated demonstrating good photocatalytic activity.

Diverse topologies of seven d10 coordination polymers constructed from a long ligand and different carboxylates

Seven d¹⁰ coordination complexes exhibiting diverse architectures from 1D chain to 3D entangled frameworks based on long flexible 1,10-bis(1,2,4-triazol-1-yl)decane and different carboxylate anions have been synthesized and characterized by single-crystal X-ray diffraction analyses.

Recent advances in porous polyoxometalate-based metal–organic framework materials

POM-based MOF materials, which combine the advantages of both POMs and MOFs, have received increasing attention. In this review, we present the recent developments in porous POM-based MOF materials for the first time, including their classification, synthesis strategies and applications, especially in the field of catalysis.

Syntheses, structures and photocatalytic properties of five new praseodymium–antimony oxochlorides: from discrete clusters to 3D inorganic–organic hybrid racemic compounds

Presented here are five Pr–Sb–O–Cl cluster-based compounds with structures from discrete organic-decorated cluster to 3D framework that exhibit photocatalytic H₂-evolution activity and magnetic properties.

Methane storage in advanced porous materials

The need for alternative fuels is greater now than ever before. With considerable sources available and low pollution factor, methane is a natural choice as petroleum replacement in cars and other mobile applications. However, efficient storage methods are still lacking to implement the application of methane in the automotive industry. Advanced porous materials, metal-organic frameworks and porous organic polymers, have received considerable attention in sorptive storage applications owing to their exceptionally high surface areas and chemically-tunable structures. In this critical review we provide an overview of the current status of the application of these two types of advanced porous materials in the storage of methane. Examples of materials exhibiting high methane storage capacities are analyzed and methods for increasing the applicability of these advanced porous materials in methane storage technologies described.