A Metal-Organic Complex Constructed from Co(II), Azo-amide-pyridyl and Benzenetricarboxylate Mixed Ligands: Efficient Catalysis for Selective Oxidation of Benzyl Alcohols to Benzyl Acids

By using one-step hydrothermal synthesis, a novel metal-organic complex containing Co(II), the azo-amide-pyridyl ligand (E)-4,4'-(diazene-1,2-diyl)bis(N-(pyridin-3-yl)benzamide (DABA) and benzenetricarboxylate was synthesized, with a molecular formula of [Co2 (DABA)0.5 (MTC)(μ3 -OH)(H2 O)2 ] ⋅ 2H2 O (namely 1, DABA=(E)-4,4'-(diazene-1,2-diyl)bis(N-(pyridin-3-yl)benzamide, H3 MTC=1,2,4-benzenetricarboxylic acid) which was characterized by single crystal X-ray diffraction, PXRD, IR spectroscopy, TGA, and XPS. In the structure of complex 1, tetranuclear Co(II) clusters were connected by MTC to form a 2D bilayer structure and further constructed a 3D structure with DABA ligand. Complex 1 was used as an efficient heterogeneous catalyst for the oxidation of benzyl alcohol, and the conversion rate of benzyl alcohol reached 98.6 % and the selectivity of benzoic acid reached 94.8 %. In addition, complex 1 can be reused 5 times without significant loss of activity. The oxidation of benzyl alcohol with different substituents also showed satisfactory conversion and selectivity, indicating that complex 1 had good catalytic performance.

Cobalt complexes tuned by Anderson-type polyoxometalates and bis-amide derivative ligands featuring a 'V'-like connector for efficient ampere sensing and the visible-light catalytic reduction of Cr(VI)

To exploit polyoxometalate (POM)-based metal-organic complexes (MOCs) with outstanding electro- and photo-chemical performances, two new bis-amide derivative N-donor ligands featuring a 'V'-like connector, 4,4'-bis(3-pyridinecarboxamide)phenylmethane (L¹) and 4,4'-bis(3-pyridinecarboxamide)phenylketone (L²), were designed and reacted with Anderson-type POMs in the presence of Co(II) ions under solvothermal conditions, which generated four MOCs: [Co₂(L¹)₂(AlMo₆H₅O₂₄)]·4H₂O (1), [Co₂(HL¹)₂(H₂O)₆(TeMo₆O₂₄)]·2H₂O (2), [Co₂(HL²)₂(H₂O)₄[AlMo₆H₆O₂₄]₂]·5H₂O (3), and [Co₂(HL²)₂(H₂O)₆(TeMo₆O₂₄)]·2H₂O (4). All the complexes showed supramolecular structures via hydrogen bond interaction, which resulted from the 2D layers for 1, the satellite-like structural units for 2 and 4, but the 1D chains for 3. In these structures, the POMs and organic ligands exhibited different coordination modes. Both 2 and 4 showed efficient ampere sensing activities for Cr(VI) with lower limits of detection of 0.029 and 0.038 μM, respectively. Complexes 1 and 2 showed good visible-light catalytic behavior toward the reduction of Cr(VI), which offers more chances for developing electrochemical sensors and photocatalysts for Cr(VI).

Research Progress on Catalytic Water Splitting Based on Polyoxometalate/Semiconductor Composites

In recent years, due to the impact of global warming, environmental pollution, and the energy crisis, international attention and demand for clean energy are increasing. Hydrogen energy is recognized as one of the clean energy sources. Water is considered as the largest potential supplier of hydrogen energy. However, artificial catalytic water splitting for hydrogen and oxygen evolution has not been widely used due to its high energy consumption and high cost during catalytic cracking. Therefore, the exploitation of photocatalysts, electrocatalysts, and photo-electrocatalysts for rapid, cost effective, and reliable water splitting is essentially needed. Polyoxometalates (POMs) are regarded as the potential candidates for water splitting catalysis. In addition to their excellent catalytic properties and reversibly redox activities, POMs can also modify semiconductors to overcome their shortcomings, and improve photoelectric conversion efficiency and photocatalytic activity, which has attracted more and more attention in the field of photoelectric water splitting catalysis. In this review, we summarize the latest applications of POMs and semiconductor composites in the field of photo-electrocatalysis (PEC) for hydrogen and oxygen evolution by catalytic water splitting in recent years and take the latest applications of POMs and semiconductor composites in photocatalysis for water splitting. In the conclusion section, the challenges and strategies of photocatalytic and PEC water-splitting by POMs and semiconductor composites are discussed.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

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

A multifunctional colorimetric sensor originating from a cadmium naphthalene diimide-based metal–organic framework: photochromism, hydrochromism, and vapochromism

A new cadmium metal–organic framework with photocontrolled luminescence properties and multiple chromic properties was synthesized for used as a multifunctional colorimetric sensor and provide a new route to design functional MOFs.