Photocatalytic technology is widely studied, while it comes with drawbacks such as low sunlight utilization efficiency and high carrier recombination rates. Herein, for the first time, we present two crystalline polyoxometalate (POM)-based metal−organic frameworks (POMOFs), {[Cd(DMF) 2 Ru(bpy) through assembling the photosensitizer [Ru-(bpy) 2 (H 2 dcbpy)]Cl 2 and POMs into a single framework. The assembly not only enhances light absorption in the visible light regime but also improves carrier separation efficiency; atop of that, both POMOFs demonstrate activities in the photocatalytic oxidative coupling of amines. Particularly, PMo-1 enables the quantitative completion of oxidative coupling of benzylamine reaction within 30 min (yield = 99.6%) with a high turnover frequency (TOF = 6631.6 h −1 ). To our knowledge, the PMo-1 catalyst outperforms any other photocatalysts previously reported in similar use cases where TOF values were usually obtained <2000 h −1 .

A novel binuclear ruthenium-based polyoxometalate, K6H­[{Ru2Cl­(H2O)­(CH3COO)2}­{WO­(H2O)}2(PW9O34)2]·14H2O (1), was successfully synthesized by the conventional hydrothermal method. Compound 1 was well-characterized by single-crystal X-ray diffraction, X-ray powder diffraction (PXRD), infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), electrospray ionization-mass spectrometry (ESI-MS), thermogravimetric analyses (TGA), and elemental analysis. The structural unit of compound 1 contains two [A-α-PW9O34]9– building blocks at the upper and lower positions connected by two W atoms and two Ru atoms, where the W atoms and Ru atoms are arranged in a trapezoidal arrangement and the Ru atoms are bridged by acetic acid. Furthermore, compound 1 features characteristic absorption bands in the visible region, which allows the investigation of its photocatalytic properties in visible light. Under simulated sunlight radiation (λ > 400 nm), compound 1 exhibits high photocatalytic activity and good circularity toward the oxidative coupling of amines to imines at room temperature with O2 as the sole oxidant.

A synchronous crystal- and microstructure-dependent strategy was implemented to synthesize the organic hybrid antimoniotungstate layered ionic crystal Na5.5H6.5[(SbW9O33)2{WO2(OH)}2{WO2}­RuC7H3NO4]·36H2O, and the layered structure was constructed through the Na+ bridged sheet and the hydrogen-bonded layers. It displayed an effective proton conductivity of 2.97 × 10–2 S cm–1 at 348 K and 75% RH, owing to the complete interlayer confined hydrogen-bond network formed by the hydrogens of interlayer crystal waters, organic ligands ({RuC7H3NO4}2+, {C7H3NO4} is formed by the hydrolysis of pyridine 2,5-dicarboxylic acid (C7H5NO4)), and acidic protons (H+), along with the interlayer domain as a transport channel. Furthermore, the hydrogen-bond network originating from interlayer organic ligands and acidic protons was more stable at a higher temperature of 423 K, preserving a high conductivity of 1.99 × 10–2 S cm–1.

Three Ru-induced structural interconversion polyoxometalates (POMs), Na 13 H 5 [Ru 4 (H 2 O) 2 (Cl) 2 (WO 2 ) 4 (AsW 9 O 33 ) 4 ]• 43H 2 O (1), K 5 Na 9 H 8 [Ru 2 (WO 2 ) 4 (AsW 9 O 33 ) 4 ]•50H 2 O (2), and KNa 13 H 14 [(WO 2 ) 4 (AsW 9 O 33 ) 4 ]•34H 2 O (3), were successfully synthesized and thoroughly characterized. Interconversion of structures was accomplished by changing the number of active sites for compounds 1− 3. All three compounds contain one {As 4 W 40 O 140 } unit, showing similar structural characteristics except for the active center number (Ru).Interestingly, compound 1 [turnover number (TON)= 486; turnover frequency (TOF)= 20 h −1 ] showed highly efficient photocatalysis in achieving oxidative coupling of primary amines. Compound 2 (TON = 406, TOF = 17 h −1 ) was also found to promote the oxidative coupling with relatively poor efficiency; however, compound 3 (TON = 178; TOF = 7.4 h −1 ) had no obvious contribution to the coupling reaction system, and a chain of evidence indicates that the catalytic performances are strongly dependent on element contents of active sites. Furthermore, the Ru-containing POM-based photocatalysts are conveniently recyclable and reusable during the photocatalytic processes. This study demonstrates the possibility of tuning the catalytic efficiency and stability of POM-based photocatalysts by well designing and controlling their structures. The possible reaction mechanism for the photocatalysis synthesis of imine product is also proposed based on experimental studies.

Two multi-Rh-incorporated polyoxometalates [NH 2 (CH 3 ) 2 ] 10 [Na 4 (H 2 O) 8 ]H 3 [As 4 W 42 O 142 (OH) 4 (CH 3 COO) 2 -Rh 3 (H 2 O) 4 ]•13H 2 O•4[NH(CH 3 ) 2 ] (1) and [K 4 Na(H 2 O) 6 ]KH 10 [As 4 W 40 O 140 Rh 4 (H 2 O) 4 ]•34H 2 O (2) have been synthesized in acetate buffer solution. Polyanion 1a is built up atop of an acetate-modified rectangular framework [As 4 W 42 O 142 (OH) 4 (CH 3 COO) 2 ] 26− , while polyanion 2a contains a pure inorganic cryptand [As 4 W 40 O 140 ] 28− . All Rh atoms of these two compounds share the same hexa-coordinate distorted-octahedral geometry and are embedded into their cavities through As−Rh bonding with a bond length around 2.304(4)−2.436(5) Å. Besides, they not only represent structural novelty but also demonstrate controllable proton conduction properties. Catalysts 1 and 2 can catalyze cycloaddition of epoxides with CO 2 in a solvent-free system in conjunction with 1-ethyl-1-methylpyrrolidinium bromide.