Decomposition-Reassembly Synthesis of a Silverton-Type Polyoxometalate 3D Framework: Semiconducting Properties and Photocatalytic Applications.

Polyoxometalate-based all-inorganic three-dimensional (3D) frameworks have recently attracted attention as a unique class of materials due to their unique physicochemical properties and a wide field of application with excellent prospects. We herein synthesized a novel all-inorganic 3D framework material based on cobalt-substituted Silverton-type polyoxometalate, H6{Co6W10O42[Co(H2O)4]3}·2H2O (Co9W10), which was successfully constructed using Na12[WCo3II(H2O)2(CoIIW9O34)2]·46-48H2O (Co5W19) and Co(NO3)2·6H2O as starting materials in a hydrothermal reaction via a decomposition-reassembly route together with the rational adjustment of pH values. Co9W10 has been structurally characterized using single-crystal X-ray diffraction. Photocurrent response, band-gap (Eg) value, and the VB-XPS spectrum have been measured to reveal the semiconducting property of Co9W10. Furthermore, we synthesized x% PTh/Co9W10 composites (PTh = polythiophene, x = 0.5, 1, 2, 5) for photodegradation of tetracycline hydrochloride (TH) to evaluate the photocatalytic activities of title composites. Due to the optimal molar ratio of hybrids and matching energy levels, 2% PTh/Co9W10 composites show the best photocatalytic activities among these composites.

pH-Controlled assembly of [ZnW12O40]6--based hybrids from a 0D dimer to a 2D network: synthesis, crystal structure, and photocatalytic performance in transformation of toluene into benzaldehyde.

Polyoxometalate-based organic-inorganic hybrids have attracted considerable attention due to their fascinating structures and wide application prospects. In this work, using the same building blocks, ligands and metal ions (ZnW12O406-(ZnW12), 2,2'-bipyridine (2,2'-bipy), and Cu2+), we synthesized three new POM-based hybrids by controlling the pH values of the reaction systems. These three compounds {(Zn0.6(H2)0.4W12O40)[Cu(2,2'-bipy)(H2O)][Cu(2,2'-bipy)(H2O)2][Cu(2,2'-bipy)(H2O)3]}2·6H2O (1), (Me4N)2{ZnW12O40[Cu(2,2'-bipy)(H2O)][Cu(2,2'-bipy)(H2O)3]}·5H2O (2), and {(Zn0.5(H2)0.5W12O40)[Cu(2,2'-bipy)][Cu(2,2'-bipy)(H2O)][Cu(2,2'-bipy)(H2O)2]}·5H2O (3) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a dimeric cluster structure, while compounds 2 and 3 appear as a 1D chain structure and a 2D network, respectively. The semiconducting properties of compounds 1-3 are different, which was demonstrated by band gap (Eg) and photocurrent response measurements. Compound 3 can efficiently catalyze the photooxidation of toluene to benzaldehyde with high selectivity using molecular oxygen as the oxidant component. Moreover, compound 3 was recycled and reused three times without significant degradation in conversion and selectivity. In addition, the mechanism of the photocatalytic reaction was also investigated.

An unprecedented polyoxometalate-based 1D double chain compound with opposite charges enables conductivity improvement.

A POM-based one-dimensional (1D) chain compound, {BW12O40[Cu(2,2'-bipy)2]2[Cu(2,2'-bipy)(H2O)]}{BW12O40[Cu(2,2'-bipy)2][Cu(2,2'-bipy)(H2O)2]}·7H2O, has been synthesized and structurally characterized, which represents an unprecedented 1D double chain structure with opposite charges. In contrast to common POMs, this compound exhibits a relatively high electrical conductivity of 1.17 × 10-9 S cm-1 at 25 °C. In addition, its semiconducting properties have also been investigated by application of photoelectrochemical sensing of H2O2.

Exploring the Coordination Modes of a Keggin-Type [ZnW12O40]6- Anionic Cluster: Bonding Patterns, Crystal Structure, and Semiconducting Properties.

Polyoxometalate-based organic-inorganic hybrid compounds (POIHCs) have been greatly developed due to their wide application prospects, but the pursuit of their directed synthesis via molecular design still remains a challenge. Herein, we demonstrate that the coordination modes of the Keggin-type [ZnW12O40]6- anion can be tuned, which leads to different semiconductor characteristics. Using the same building block, ligand, and metal ion (ZnW12, phen, Cu2+), we synthesized three new POIHCs with different bonding patterns by means of different coordination modes of ZnW12. The three POIHCs (H2phen){ZnW12O40[Cu(phen)2]2}·3H2O (1), {ZnW12O40[Cu(phen)(H2O)2]2[Cu(phen)(H2O)]}n·3H2O (2), and (Me4N)2{ZnW12O40[Cu(phen)(H2O)]2}n·5H2O (3) (phen = 1,10-phenanthroline) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a zero-dimensional coordination complex cluster, while compounds 2 and 3 are both 1D chain structures with different Cu2+ bridge linkages. Although these three POIHCs possess the same chemical components, their semiconductor properties are different, which is demonstrated by measurements of transient photocurrent and band gap (Eg) values. Furthermore, we carried out comparative experiments on the photoconductivity performance of compounds 1-3 and their photocatalytic reduction from O2 to H2O2, indicating the significant influence of the energy level matching on the photocatalytic activity.

Rationally Designing Metal-Organic Frameworks Based on [Ln2] Magnetic Building Blocks Utilizing 2-Hydroxyisophthalate and Fine-Tuning the Magnetic Properties of Dy Analogues by Terminal Coordinated Solvents.

By utilizing the 2-hydroxyisophthalic acid (H3ipO) ligand, 2D metal-organic frameworks (MOFs) featuring rare Ophenol-bridged [Ln2]-magnetic building blocks (MBBs), [Ln2(ipO)2(DMF)(H2O)] [Ln = Gd (1), Dy (2); DMF = N,N-dimethylformamide], were rationally designed and synthesized. When the reaction solvents that behave as terminal ligands were changed, the coordination geometries of LnIII ions and the arrangement fashion of [Ln2]-MBBs for these MOFs were modified accordingly. Another type of 2D MOF of [Ln2(ipO)2(H2O)4]·2H2O [Ln = Gd (3), Dy (4)] was thus obtained. MOFs 1 and 3 exhibited favorable magnetocaloric effect, whose maximum -ΔSm values reach 30.0 and 31.7 J kg-1 K-1, respectively. None of the single-molecule-magnet (SMM) behavior was observed in 2. However, from 2 to 4, the change of the terminal coordinated solvents brought obvious improvement of the magnetic properties. MOF 4 showed interesting relaxation behavior, in which dual relaxation was only visible under weak direct-current fields, and its highest effective energy barrier (Ueff) reached up to 243 K. Ab initio calculations revealed the tuning mechanism of the terminal coordinated solvents. Their change optimized the arrangements of the magnetic axis of the DyIII centers in both each MBB and the whole framework, thus improving the magnetic anisotropy and magnetic interactions of the system. Significantly, within the [Dy2]-MBBs of 4, the angle made by the individual magnetic axis and Dy···Dy' line is nearly 0°. This case favoring a high SMM performance not only was scarcely achieved in discrete {Ln2}-SMMs with numerous members but also has never been observed in any MBB-based MOFs as far as we know.