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.

{Mo4}-directed structural evolution of highly reduced molybdenum red clusters for efficient proton conduction

A series of highly reduced Mo red clusters {Mo28} (1), {Mo30} (2), and {Mo40} (3) are synthesized from the rational assembly of planar {MoV4} building blocks and employed for proton conduction. 3 exhibits the best conductivity of 7.56 × 10-3 S cm-1 under optimal conditions due to the most efficient hydrogen-bonding network.

A wheel-shaped Zr-substituted phosphotungstate [{Zr(C2O4)2}3 (PO4)(P6W39O150)]39- with tunable proton conduction properties

A wheel-shaped Zr-substituted phosphotungstate, [N(CH3)4]2K16Na10.5H10.5[{Zr(C2O4)2}3(PO4)(P6W39O150)]·45H2O (1), was synthesised from a hexavacant Dawson-type precursor [H2P2W12O48]12-via a conventional solution method. Compound 1 features a wheel-shaped polyanion comprising an annular [P6W39O150]36- cluster supported by a turbine-shaped [{Zr(C2O4)2}3(PO4)]3- fragment, with three oxalate groups covalently anchored to W atoms. Compound 1 was systematically characterized by IR, UV, PXRD, TGA and 31P NMR spectra. The 31P NMR spectra over time were monitored to verify the stability of 1 in aqueous solution. This compound possesses remarkable proton conductive behavior with a high conductivity of 1.18 × 10-2 S cm-1 at 368 K.

Three-Dimensional Polyoxometalate Organic Frameworks with One-Dimensional Channels Constructed by Multiple Helical Chains Based on 22-Core Ln/Mn/Mo Clusters for Proton Conduction

Two unique 22-core sandwich {[Mn6Mo6O37]Ln3[MnMo6O24]} (Ln = La or Pr) units have been assembled, featuring an undisclosed {Mn6Mo6} cluster. This assembly is subsequently integrated into two three-dimensional polyoxometalate organic frameworks, which exhibit one-dimensional hydrophilic hexagonal channels formed by six intertwined 63 helical chains, leading to effective proton conduction primarily facilitated by an abundance of water molecules within the channels.

Discovery and Isolation of Two Arsenotungastate Species: [As4W48O168]36- and [As2W21O77(H2O)3]22

Two novel arsenotungstate species, [As₄W₄₈O₁₆₈]^36- (1a) and [As₂W₂₁O₇₇(H₂O)₃]^22- (2a), have been successfully isolated under a one-pot synthetic method. 1a is the second largest arsenotungstate cluster and is constructed from four {AsW₁₂} clusters combined together. 2a can be described as lacunary sites of {As₂W₁₉} filled by {W₂O₈} units. Compounds 1 and 2 exhibit proton conductivity properties, and the conductivity value of 1 is 5.0 × 10^-3 S cm^-1 at 98% relative humidity and 75 °C. This work proves that the lattice water molecules and polyoxoanions can participate in the formation of a hydrogen bond, acting as effective pathway for intermolecular proton conduction.

Proton-Conductive Polyoxometalate Architectures Constructed from Lanthanide-Incorporated Polyoxoniobate Cages

Two new extended polyoxometalate (POM) architectures based on lanthanide-incorporated polyoxoniobate (Ln-incorporated PONb) cages, namely, H₄[Cu^II(en)₂]₄{K₄(H₂O)₂[Cu^II(en)₂]₅[Cu^II₅(trz)₂(en)₄(OH)₂][Dy₂Cu^II₂(en)₂(CO₃)₃(H₂O)₂(OH)₃][Dy(H₂O)₄][DyNb₂₃O₆₈(H₂O)₄]₂}·60H₂O (1, en = ethylenediamine) and H₂₀[Cu^II(en)₂]₄{[Cu^II(en)₂]₄[Dy₂(C₂O₄)(H₂O)₄]₂[(Nb₃₂(OH)₄(H₂O)₃O₈₉]₂}·54H₂O (2), have been successfully synthesized and structurally characterized, demonstrating a feasible strategy to develop functional POM materials. In addition, the proton conductivity and magnetic behaviors of both 1 and 2 were studied.

Designed assembly of heterometallic zeolite-like framework materials from two different supertetrahedral metal clusters

This work demonstrates a feasible strategy for the synthesis of new zeolite-like framework materials. With the strategy of using two different supertetrahedral clusters as secondary building units, two new heterometallic zeolite-like frameworks with isomeric structures but tunable topologies were first made. Besides, the porous nature and the proton conduction performance of the new materials were further studied.

A Three-Dimensional (3D) Indium-Containing Polyoxoniobate Framework Based on {In5Nb71}n Helical Pillars

A rare 3D Indium-containing polyoxoniobate framework {H₉[Cu(en)₂(H₂O)₂][Cu(en)₂]₁₂[In(en)]₅[Nb₂₃-O₆₅(OH)₃(H₂O)₂]{Nb₂₄O₆₇(OH)₂(H₂O)₃]₂}·68H₂O(1), based on the In-containing polyoxoniobate cluster, {[In(en)]₅[Nb₂₃O₆₅(OH)₃(H₂O)₂][Nb₂₄O₆₇(OH)₂(H₂O)₃]₂}^35- ({In₅Nb₇₁}) and [Cu(en)₂]²⁺ linkers has been successfully synthesized. The nest-like cluster {In₅Nb₇₁} is constructed from one brand-new V-shaped {Nb₂₃O₇₀}, two triangle-shaped {Nb₂₄O₇₂} and five [In(en)]³⁺. The [In(en)] fragments link {Nb₂₄O₇₂} and {Nb₂₃O₇₀} units into unique {In₅Nb₇₁}_n helical pillars. The copper-amine complexes connect the {In₅Nb₇₁}_n helical pillars into a three-dimensional (3D) inorganic-organic hybrid In-Cu-containing framework. This material also exhibits good ionic conductivity and vapor adsorption capacity properties.

Two high-nuclearity isopolyoxoniobates containing {Nb54 O151}-based helical nanotubes for the decomposition of chemical warfare agent simulants

Two inorganic-organic hybrid isopolyoxoniobates (1 and 2) based on new high-nuclearity {Nb₅₄O₁₅₁} clusters have been synthesized under hydrothermal conditions. In particular, the combination of the unique {Nb₅₄O₁₅₁} clusters with copper-amine complexes has led to rare helical nanotubes, which are further linked by alkali metal cations or copper-amine complexes into two 2D similar bamboo-raft-like layered networks (1 and 2), respectively. Compound 1 exhibits effective base-catalytic decomposition of chemical warfare agent simulants dimethyl methylphosphonate (DMMP) and diethyl cyanophosphonate (DECP).

A Rh-substituted polyoxometalate with an acetate-modified building block {As2W22O76(CH3COO)2}

The first example of Rh-substituted organic-inorganic hybrid arsenotungstate [H₂N(CH₃)₂]₈{[Na(H₂O)₄]NaAs₂W₂₂(CH₃COO)₂O₇₆ Rh₂(N(CH₃)₂)₂}·H₂O (1) synthesised in an aqueous solution by the conventional method is reported. Two [Rh(N(CH₃)₂)]³⁺ fragments are imbedded into the vacancy of the [NaAs₂W₂₂(CH₃COO)₂O₇₆]^15- unit by Rh-As bonds [2.439(1) Å], which are observed in POM chemistry for the first time.

One-pot mechanochemical synthesis to encapsulate functional guests into a metal-organic framework for proton conduction

Through one-pot mechanochemical synthesis, a series of guests [imidazole, (aminomethyl)phosphonic acid, urea and sulfamic acid] are rapidly encapsulated into the pores of MOF NENU-3 while the MOF is formed. The synthesis of a MOF loaded with functional guests that used to take several days and require a multistep procedure can now be completed in one step within several minutes. The proton conductivities of the obtained composites increased by 2-3 orders of magnitude compared with NENU-3.

Linear and Nonlinear Optical Properties of Centrosymmetric Sb4O5SO4 and Noncentrosymmetric Sb4O4(SO4)(OH)2 Induced by Lone Pair Stereoactivity

Introducing stereochemically active lone-pair Sb³⁺ cations into sulfates, two three-dimensional (3D) antimony-sulfates, Sb₄O₅SO₄ (1) and Sb₄O(SO₄)(OH)₂ (2), were achieved under moderate hydrothermal conditions. Both structures are constructed by tetranuclear-{Sb₄}-clusters-based layers and SO₄ tetrahedra. However, owing to the different packing patterns of the layers, they display different characteristics: 1 exhibits a centrosymmetric structure while 2 possesses a noncentrosymmetric structure. UV-vis spectra show that they possess wide band gaps. Sb₄O(SO₄)(OH)₂ is nonlinear optical (NLO) active with a second-harmonic generation (SHG) response of ∼1.2 times of KH₂PO₄, together with the phase-matchable capacity, endowing it a promising UV NLO material. The first-principle calculations were performed to elucidate the structure-property relationships. The results indicate that the lone pair stereoactivity of Sb³⁺ provides the large contribution to the macroscopic SHG effect.