Organophosphonate-Functionalized Telluromolybdate Containing a [TeMo10O37]10- Building Block and Its Catalytic Efficiency for Knoevenagel Condensation

A High Nucleus Cu-Incorporated Giant Phosphotungstate with Photocatalytic Oxidation C-H of Toluene

Exploring a novel photocatalyst for catalytic oxidation of toluene is a sustainable strategy for energy conversion in times of an energy crisis. However, designing an effective photocatalyst for the conversion of toluene remains challenging. Herein, a novel organic monophosphonate-modified high nucleus Cu-incorporated polyoxotungstate, K8H33[{Cu0.5(H2O)4}{Cu2(O3PCH2COO)(1,4,9-α-P2W15O56)}]4·Cl·60H2O (1), has been intentionally synthesized by a self-assembly process utilizing conventional aqueous method. It reveals that 1 contains a polyanion of [{Cu0.5(H2O)}4{Cu2(O3PCH2COO)(1,4,9-α-P2W15O56)}]440- composed of four Dawson-type {1,4,9-α-P2W15} subunits, forming an oval-shaped structure and further connecting into a three-dimensional (3D) framework by lateral {Cu(H2O)4}2+. Interestingly, the trivacant {1,4,9-α-P2W15} subunits were observed in the organophosphonate acid-functionalized polyoxometalates for the first time. Notably, 1 exhibits a wonderful performance in catalytic oxidation of the recalcitrant C(sp3)-H bond of toluene to benzoic acid with a conversion as high as 97% under visible light utilizing O2 as an oxidant.

Synthesis and Structure of High-Nuclearity Carboxylate-Modified Heteropolyoxovanadate Serving as a Heterogeneous Catalyst for Selective Oxidation of Alkylbenzenes

A high-nuclearity carboxylic-modified heteropolyoxovanadate, Na2K10H15[P8VIV24(tart)15(H2O)15(OH)O51]·58H2O [1, tart = C4H2O6], has been successfully synthesized by a conventional aqueous method under mild conditions. The crystallographic study reveals that compound 1 crystallizes in the tetragonal I41/a space group and is composed by a trilayer saddle-like polyoxoanion {P8V24}. Two {V3(tart)(H2O)O11} as linking units bridge the top {P4VIV9(tart)7(H2O)4(OH)O23} and the bottom {P4VIV9(tart)6(H2O)9O22} layers via tartrate ligands and {PO4} tetrahedra, resulting in a 24-nuclearity POV skeleton structure. More interestingly, compound 1 serves as a heterogeneous catalyst for the selective oxidation of diphenylmethanes with 96.2% conversion and 93.6% selectivity under the optimized conditions.

Diphosphoryl-functionalized Polyoxometalates: Structurally and Electronically Tunable Hybrid Molecular Materials

Herein, we report the synthesis and characterization of a new class of hybrid Wells-Dawson polyoxometalate (POM) containing a diphosphoryl group (P2 O6 X) of the general formula [P2 W17 O57 (P2 O6 X)]6- (X=O, NH, or CR1 R2 ). Modifying the bridging unit X was found to impact the redox potentials of the POM. The ease with which a range of α-functionalized diphosphonic acids (X=CR1 R2 ) can be prepared provides possibilities to access diverse functionalized hybrid POMs. Compared to existing phosphonate hybrid Wells-Dawson POMs, diphosphoryl-substituted POMs offer a wider tunable redox window and enhanced hydrolytic stability. This study provides a basis for the rational design and synthesis of next-generation hybrid Wells-Dawson POMs.

Heteroatom-Modulated Assembly of Hexalanthanoid-Containing Polyoxometalate-Based Coordination Networks

Two series of lanthanoid (Ln)-containing polyoxometalates (POMs) {[Ln₆(ampH)₄(H₂O)_24-n(ampH₂)_n(PW₁₁O₃₉)₂]·21H₂O (Ln = Tb, n = 0 (1), Ln = Er, n = 1 (2)) and K₂[Ln₆(ampH)₄(H₂O)₂₂(SiW₁₁O₃₉)₂]·23H₂O (Ln = Tb (3), Er (4)) (ampH₂ = (aminomethyl) phosphonic acid)} have been synthesized with tri-lacunary Keggin-type POMs containing different types of heteroatoms. Compounds 1 and 2 display neutral organic-inorganic hybrid POM molecules containing {Ln₆(ampH)₄} ({Ln₆}) cores sandwiched by two {PW₁₁O₃₉} units. By changing the heteroatoms from P^V to Si^IV, the extended 2D networks of 3 and 4 were successfully isolated where the adjacent {Ln₆} clusters were connected by {SiW₁₁O₃₉} moieties. Luminescence performances and magnetic properties of 1-4 have been systematically surveyed. The solid-state fluorescence spectra of 1-4 display characteristic emissions of Ln components resulting from the 4f-4f transitions, and energy transfer from the POM segments to Ln³⁺ centers in 1 and 3 has been observed based on the lifetime decay behaviors. Furthermore, all compounds can be utilized as electrocatalysts toward reduction of nitrite with high stability.

Polyphosphazene-Functionalized Microspheres as Efficient Catalysts for the Knoevenagel Reaction under Mild Conditions

Inspired by the formation of microspheres by hexachlorocyclotriphosphazene and 4, 4'-sulfonyldiphenol, polyphosphazene-functionalized microspheres were developed. Benefits from the supported supper basic phosphazene, the yield exceeded 99 % at room temperature in the manner of second-order reaction kinetics toward Knoevenagel reaction and was still maintained at 99 % after 16 runs. In the experimental temperature from 0 °C to 90 °C, the yield increased from 92 % to 99 %, reflecting that the catalyst had strong applicability under mild conditions. This behavior was conducive to energy conservation. Meanwhile, simple separation and recovery further enhanced this advantage. In addition, the catalyst was also found to be insensitive to aqueous solution or organic solvents such as toluene, THF, EtOH and CH₃ CN. This property gave the Knoevenagel reaction a vast choice. All these features exhibit that this novel catalyst is an attractive and applicable alternative in organic synthesis.

2D Windmill-like Ln-Containing Organophosphonate-Based Polyoxomolybdates: Synthesis, Characterization, Fluorescence, and Magnetism

By integration of {Ln(H₂O)₆}³⁺ into organophosphonate-based polyoxometalates, three Ln-containing organophosphonate-functionalized polyoxomolybdates Na_1.5H_1.5[{Ln(H₂O)₆}₂{(Mo₃O₈)(O₃PC(C₃H₆NH₃)OPO₃)}₄]·(CH₃CO₂)·43H₂O (Ln = Eu (1), Tb (2), and Dy (3)) are successfully prepared and systematically characterized. The X-ray crystallography analyses display complexes 1-3 crystallize in the C2/c space group of the monoclinic system and compose several distinctive tetramer windmill-like compounds that further assemble into two-dimensional (2D) frameworks associated with the {Ln(H₂O)₆}³⁺ core. The fluorescence spectra of 1-3 show red, green, and chartreuse emissions, respectively, originating in the typical f-f transitions of Ln³⁺ ions. More interestingly, complex 3 shows the field-induced single-molecule magnet (SMM) properties, resulting from the fact that [(Mo₃O₈)₄{O₃PC(C₃H₆NH₃)OPO₃}₄]^8- offers excellent magnetic isolation for Dy³⁺ ions by the nearest Dy1···Dy2 distance of 11.207 Å. The study demonstrates that the incorporation of {Ln(H₂O)₆}³⁺ into organophosphonate-based polyoxomolybdates is an effective synthetic strategy in implementing late-model opto-magnetic materials.

High-Nuclear Ni-Substituted Poly(polyoxometalate) Containing an Anderson-like {Cs7} Cluster

A novel high-nuclear Ni-substituted poly(polyoxometalate) [poly(POM)], [H₂N(CH₃)₂]₂Na₁₈Cs₂H₁₃[(Cs₇(H₂O)₆)@{(PO₄)-@(Ni₄(OH)₃(WO₄))₃@(B-α-PW₉O₃₄)₃}₂]·30H₂O (1), has been successfully developed and structurally characterized. The polyoxoanion of 1 can be viewed as a unique huge sandwich structure made of an unprecedented Cs₇(H₂O)₆ ({Cs₇}) cluster core encapsulated by two trimeric [(PO₄)@(Ni₄(OH)₃(WO₄))₃@(B-α-PW₉O₃₄)₃]^21- subunits, in which the {Cs₇} cluster presents an interesting Anderson-like arrangement and is the first example of a classical POM configuration based on the alkali metal cluster in the POM chemistry. The polyoxoanion can also be described as an unusual [(Cs₇(H₂O)₆)@{(PO₄)@(Ni₄(OH)₃(WO₄))₃}₂]¹⁹⁺ cluster packaged by six {PW₉} fragments. Furthermore, investigations on the Knoevenagel condensation reaction reveal that 1 has good catalytic activity for the condensation of various aldehydes and malononitrile into corresponding products with excellent yields.

Organic-inorganic one-dimensional hybrid aggregates constructed from aromatic-bisphosphonate-functionalized polyoxomolybdates

Five novel lanthanide-substituted polyoxomolybdates (NH₄)₅Na₃H₂[{Ln(H₂O)₇}₂{Mo₅O₁₅(1,4-O₃PCH₂C₆H₄CH₂PO₃)}₄]·nH₂O [Ln = Tb³⁺ (1), Ho³⁺ (2), Er³⁺ (3), Tm³⁺ (4), Yb³⁺ (5); n = 33, 32, 41, 30, 47] have been prepared in a conventional aqueous solution reaction of ammonium molybdate with Ln³⁺ ions and p-xylyenediphosphonic acid. Crystal structure analyses reveal that 1-5 are isomorphic. The prominent architecture characteristic is that their structural units consist of a tetrameric cyclic-shaped [{Mo₅O₁₅(1,4-O₃PCH₂C₆H₄CH₂PO₃)}₄]^16- segment stabilized by two [Ln(H₂O)₇]³⁺ cations, which are connected to propagate one-dimensional chain by Ln³⁺ ions. As is known, compounds 1-5 stand for the first Ln-substituted aromatic-bisphosphonate-functionalized polyoxomolybdates. The solid-state photoluminescence measurement of 1 has been performed at ambient temperature, and it displayed the characteristic emissions of Tb ions based on its 4f-4f transitions. In addition, the magnetic properties of 1-5 compounds show that they all exhibit anti-ferromagnetic interactions.