SO₃^2-/SeO₃^2-/TeO₃^2- Template-Based Nanoscale High-nuclearity Polyoxotungstate Clusters:Synthesis,Assembly,and Property

Nanoscale high-nuclearity polyoxotungstates（POTs）clusters,as one kind of important polyoxometalates（POMs）chemistry,have already been used in the area of moleculer magnets,catalysis,energy storage and nanomaterials.The key factor of design and synthesis of novel POM-based clusters with unique functionalities is how to obtain secondary building units for the construction of high-nuclearity POTs clusters,XO₃-templated（X = SIV,SeIV and TeIV）synthetic approaches can resolve this problem ideally.The redox active heteroanions are trigonal and accept only three bonds with oxygen,with a presumably stereochemically directing lone pair based on the X center.The POTs lacunary fragments can be generated in situ in solution,it lays the foundation of the formation of secondary building units,thus the obtained crystalline materials enrich the applications of nanoscale high-nuclearity POTs clusters in the formation of micron-scale tubes,unimolecular reaction,memory devices,etc.,which have became a key emerging area and hotspot in POM chemistry.In this paper,a conventional reaction condition is employed to synthesize a series of nanoscale high-nuclearity POTs-based crystalline materials.The synthetic and assembly rules for these materials have been studied in detail,their electrochemical properties,supramolecular assemblies,magnetic properties,photocatalytic H2 evolution activity and visible light-driven water oxidation have also been investigated.1.Five Ce（Ⅲ）-containing POTs have been isolated depending on the pH values by combing the pH-controlled and {SO₃^2-}-directed assembly strategy along with Ce（Ⅲ）centers.Compound 4 remains the first Ln-containing POTs with sulfur heteroatom,and 5 presents the largest lanthanide（Ln）-containing iso-POTs.In addition,BVS,elemental analysis,EPR spectra,XPS spectra,and DFT calculations indicate that the oxidation states of Ce（Ⅲ）centers in 1-5.Moreover,electrochemical properties of all the compounds indicated that Ce（Ⅲ）oxidation potential correlates the size of coordinated iso-POT ligands.（C2H8N）3Na7[Ce2（H2O）6W22O72（OH）4]?20H2O（1）（C2H8N）8Na16[Ce4（H2O）12W44O144（OH）12]?23H2O（2）（C2H8N）2Na4Ce2[Ce2（H2O）10W28O92（OH）2]?27H2O（3）（C2H8N）2Na7[{α-SW₇O28}{Ce2（H2O）6}（W3O6）{α-SW9O₃2}{α-SW9O₃1（OH）}]?18H2O（4）（C2H8N）2Na18[Ce2（H2O）9W36O110（OH）12]2?30H2O（5）2.Six Ce（Ⅲ）-containing large purely inorganic POTs based on SeO₃^2-/TeO₃^2-heteroanion templates have been synthesized by combining Ce linkers and SeO₃^2-/TeO₃^2-heteroanion templates for the first time.It is a breakthrough in preparation of Ln-containing POTs with selenium-and tellurium-based heteroanions.The behaviors of compounds 8-10 insolution are studied by transmission electron microscopy,which show that their single polyoxoanions assemble into intact,uniformsized,purely inorganic hollow spheres in dilute water/acetone solution for the first time.K6Na16[Ce₆Se₆W67O230（OH）6（H2O）17]?47H2O（6）K9Na5Ce（H2O）4[Ce6Se10W51O187（OH）7（H2O）18]?45H2O（7）K32Na16[Ce8Se8W88O₃16（H2O）20]?81H2O（8）K32Na16[Ce8Te8W88O₃16（H2O）20]?114H2O（9）K12Na22[Ce12Se12W88O₃22（H2O）34（NO₃）2}]?79H2O（10）Na18[Ce10Te8W88O298（OH）12（H2O）40]?54H2O（11）3.Two FeIII-substituted Wells–Dawson-type nanoscale selenotungstate clusters have been obtained by combining Fe centers and SeO₃^2-heteroanion templates.They represent the first examples of FeIII-substituted Wells–Dawson-type selenotungstate clusters.Compound 13 possesses more tungsten centers than any other known FeIII-substituted Wells–Dawson-type POTs.They possess similar antiferromagnetic coupling within FeIIIcenters.The stabilities of both compounds in water were investigated by UV/Vis spectroscopy and ESI-MS.The diffusereflectance UV-vis spectra of the powder samples 12 and 13 reveal the presence of an optical band gap and the nature of semiconductivity.The H2 evolution rate with the use of 12 or 13 is higher than that of the isolated Wells–Dawson-type selenotungstate {Se4W36} cluster,which clearly indicates the positive effects of 12 or 13 with the introduction of Fe3+ centers on the photocatalytic activity.（C2H8N）4Na14[Fe6Se₆W34O124（OH）16]?44H2O（12）（NH4）9Na19[Fe10Se8W62O222（OH）18（H2O）4]?42H2O（13）4.We isolated two distinct compounds by carefully controlling the reaction parameters under one-pot conditions from simple precursors（from the same one-pot reaction）.Compound 14 contains unreported {SeW4} and {SeW₇} species,and subsequent connections to form novel Wells-Dawson-type-like {Se₂W₁₁} fragments.Compound 15 remains a trimeric wheel-type aggregate based on a new type of {Se₂W12}-based crown {Se₆W38} shell.As a new type of all-inorganic and stable Mn-containing POM-based homogeneous photocatalysts for proton reduction,they both exhibit excellent photocatalytic H2 evolution activity.K2Na10[K2?{Mn Se4W23O85（H2O）6}]?29H2O（14）K2Na10[K2?{Mn3Se7W39O131（OH）20（H2O）2}]?60H2O（15）5.Three unprecedented Wells–Dawson-type dimethyltin-functionalized organic–inorganic hybrid selenotungstates have been obtained by combining organotin species and SeO₃^2-heteroanion templates for the first time.Compounds 16 and 17 are trimeric or tetrameric nanocluster,respectively,while compound 18 exhibits 1D chain.Compounds 17 and 18 are the second largest dimethyltin-containing POMs to date.Moreover,they also exhibit excellent photocatalytic H2 evolution activity in water/methanol system.（C2H8N）9Na9[{Sn（CH3）2（CH3COO）}3{Sn（CH3）2}3{Se₂W18O62（OH）（H2O）}3]?25H2O（16）（C2H8N）7Na12[{Sn（CH3）2}4{Sn（CH3）2（H2O）}2{Sn（CH3）2（H2O）2}Se8W54O191（OH）7（H2O）2]?64H2O（17）（C2H8N）8Na10[{Sn（CH3）2}10{Sn（CH3）2（H2O）}6Se11W56O211（OH）8]?105H2O（18）6.A carbon-free,homogeneous POM water oxidation catalyst with a cobalt–arsenic core for photocatalytic water oxidation has been synthetized.It represents the first cobalt–arsenic core in POM area,a novel hepta-nuclear cobalt ‘‘fused’’ double-quasi-cubane-type topology,and a new type of soluble carbon-free molecular water oxidation catalyst based on the earth abundant metal elements.The ultraviolet photoelectron spectroscopy and UV-vis spectroscopy measurements were carried out to gain more insights into the energy levels for supporting the utilization in visible light-driven water oxidation.Under our tested conditions,the TON（115.2）and initial turnover frequency（TOFinitial,0.14 s-1）values are comparable to the reported Co-based quasi-cubane-or cubane-type water oxidation catalysts.Moreover,multiple and complementary experiments are needed to determine the catalyst stability,for example,aging experiments,dynamic light scattering measurements,etc.,these results show the water oxidation catalyst remains stable under the photocatalytic water oxidation conditions.Na12[{Co II7 As III6O9（OH）6}（A-α-Si W9O₃4）2]?8H2O（19）...