Assembly of Tungsten‐Oxide‐Based Pentagonal Motifs in Solution Leads to Nanoscale {W48}, {W56}, and {W92} Polyoxometalate Clusters

We report an approach to synthesize molecular tungsten‐oxide‐based pentagonal building blocks, in a new {W₂₁O₇₂} unit, and show how this leads to a family of gigantic molecular architectures including [H₁₂W₄₈O₁₆₄]^28? {W₄₈}, [H₂₀W₅₆O₁₉₀]^24? {W₅₆}, and [H₁₂W₉₂O₃₁₁]^58? {W₉₂}. The {W₄₈} and {W₅₆} clusters are both dimeric species incorporating two {W₂₁} units and the {W₅₆} species is the first example of a molecular metal oxide cluster containing a chiral “double‐stranded” motif which is stable in solution as confirmed by mass spectrometry. The {W₉₂} anion having four {W₂₁} units is one of the largest transition metal substituted isopolyoxotungstates known.     

Structural Link between Giant Molybdenum Oxide Based Ions and Derived Keggin Structure: Modular Assemblies Based on the [BW11O39]9− Ion and Pentagonal {M′M5} Units (M′=W; M=Mo,W)

Linked to the Pentagon : The addition of molybdate to [HBW₁₁O₃₉]^8? ions leads to the formation of mixed pentagonal units {W(Mo₅)} and {W(WMo₄)} trapped as linkers in the resulting modular assemblies, thus establishing the first link between the conventional Keggin ion derivatives and the giant molybdenum oxide and keplerate ions.

     

Synthesis,Structure and Light-Driven H2 Production of a {Ti21} Titanium-Oxo Cluster Featuring Pentagonal {Ti(Ti5)} Motifs

Pentagonal {Ti(Ti₅)} motifs play a crucial role during the assembly of novel titanium-oxide clusters (TOCs), whose development is still in its infancy. In this work, an unprecedented TOC [(CH₃)₂NH₂]₂[Ti₂₁O₂₉(OiPr)₁₂(DMF)₆(SO₄)₈] ({Ti₂₁}) based on {Ti(Ti₅)} motifs had been obtained under hydrothermal conditions. It possesses ‘fused’ dimeric {Ti₁₁} as well as trimeric {Ti₁₂} subunits featuring unexpected bonding modes based on pentagonal {Ti(Ti₅)} motifs. Furthermore, {Ti₂₁} exhibits good water and solvent tolerance. As an atomically precise TOCs-based semiconductor photocatalyst, {Ti₂₁} exhibits appreciable photocatalytic hydrogen evolution activity with an optimal hydrogen generation rate of 191.94 μmol/g/h under UV/Vis light. This work provides significant advances and favorable models for the further synthesis of TOCs with unique structure and functionality.     

Unprecedented Selenium and Lanthanide Simultaneously Bridging Selenotungstate Aggregates Stabilized by Four Tetra‐vacant Dawson‐like {Se2W14} Units

In the presence of the larger [H₂N(CH₃)₂]⁺ and K⁺ counter cations as structure‐stabilizing agents, a class of unprecedented selenium and lanthanide (Ln) simultaneously bridging tetra‐vacant Dawson‐like selenotungstate aggregates [H₂N(CH₃)₂]₂Na₉K₂H₁₉{[Ln₄W₄ Se₄O₂₂(H₂O)₅](Se₂W₁₄O₅₂)₂}₂ ⋅ 60 H₂O [Ln=Tb^III ( 1 ), Dy^III ( 2 ), Ho^III ( 3 ), Er^III ( 4 ), Tm^III ( 5 ), Yb^III ( 6 )] have been obtained by the one‐pot assembly reaction of Na₂WO₄ ⋅ 2 H₂O, Ln(NO₃)₃ ⋅ 6 H₂O, and Na₂SeO₃ under moderately acidic aqueous conditions and the complexes were structurally characterized by elemental analyses, IR spectra, single‐crystal X‐ray diffraction, powder X‐ray diffraction (PXRD), and thermogravimetric (TG) analyses. It should be noted that the appropriate molar ratio of Se/W is extremely important in the formation of 1 – 6 and can effectively ameliorate the yield of 1 – 6 . Moreover, dimethylamine hydrochloride is also indispensable and plays a considerably important role in improving the solubility of Ln ions and stabilizing the structures of 1 – 6 . The main polyoxoanion skeletons of 1 – 6 are constructed from two sandwich‐type tetra‐vacant Dawson‐like {[Ln₄W₄Se₄O₂₂(H₂O)₅](Se₂W₁₄O₅₂)₂}¹⁶⁻ half‐units linked through two W‐O‐Ln bridges. The sandwich‐type half‐unit comprises two tetra‐vacant Dawson‐like [Se₂W₁₄O₅₂]¹²⁻ fragments encapsulating a unique dodecanuclear Se‐Ln‐W [Ln₄W₄Se₄O₂₂(H₂O)₅]⁸⁺ oxo cluster. Their solid‐state visible and NIR fluorescent properties and lifetime decay behaviors were measured and their solid‐state luminescent spectra mainly demonstrate the characteristic emission bands of Ln³⁺ ions. Moreover, the dominant wavelengths, the color purity, and correlated color temperatures of 1 – 5 have been also calculated. In addition, the luminous flux values of 1 – 5 are 2031, 6992, 3071, 921, and 477 lumen, respectively.     

Nanoscale Control of Polyoxometalate Assembly: A {Mn8W4} Cluster within a {W36Si4Mn10} Cluster Showing a New Type of Isomerism

Two near isomeric clusters containing a novel {Mn₈W₄} Keggin cluster within a [W₃₆Mn₁₀Si₄O₁₃₆(OH)₄(H₂O)8]^24? cluster are reported: K₁₀Li₁₄ [W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1 ) and K₁₀Li1_3.5Mn_0.25[W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1′ ). Bulk characterization of the clusters has been carried out by single crystal X‐ray structure analysis, ICP‐MS, TGA, ESI‐MS, CV and SQUID‐magnetometer analysis. X‐ray analysis revealed that 1′ has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two “intermediate” types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X‐ray analysis and revealed to be novel clusters K₄Li₂₂[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?56 H₂O ( 2 ) and Mn₂K₈Li₁₄[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?45 H₂O ( 3 ). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X‐ray crystallography directly facilitated understanding the means by which a POM assembled.     

Assembly of a family of mixed metal {Mo:V} polyoxometalates templated by TeO3(2-): {Mo12V12Te3}, {Mo12V12Te2} and {Mo17V8Te}

The influence of the pyramidal heteroanion, TeO(3)(2-) in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo(12)V(12)Te(3)} (1), {Mo(12)V(12)Te(2)} (2) and {Mo(17)V(8)Te} (3) with the tellurium centres exhibiting the novel μ(8)-TeO(4) and μ(9)-TeO(3) coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry.     

Three Cobalt(II)‐Linked {P8W48} Network Assemblies: Syntheses,Structures, and Magnetic and Photocatalysis Properties

Three cobalt(II)‐containing tungstophosphate compounds, Na₈Li₈Co₅[Co_5.5(H₂O)₁₉P₈W_48.5O₁₈₄] ? 60 H₂O ( 1 ), K₂Na₄Li₁₁Co₅[Co₇(H₂O)₂₈P₈W₄₈O₁₈₄]Cl ? 59 H₂O ( 2 ), and K₂Na₄LiCo₁₁[Co₈(H₂O)₃₂P₈W₄₈O₁₈₄](CH₃COO)₄Cl ? 47 H₂O ( 3 ), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, elemental analyses, and magnetic measurements. The pH value impacts the formation of distinct cobalt‐linked frameworks. The cyclic cavity of the polyanion accommodates 5.5, 7, and 8 cobalt ions in 1 , 2 , and 3 , respectively. In compounds 1 and 2 , each {Co_5.5P₈W₄₈} and {Co₇P₈W₄₈} fragment links to four others through multiple {Co‐O‐W} coordination bonds to generate a two‐dimensional network. Compound 3 can be considered as a 3D network based on the {Co‐O‐W} coordination bonds and the {Co₃(CH₃COO)₂(H₂O)₁₀} linkers between the {P₈W₄₈} fragments. Interestingly, acetate ligands have been employed to form the {Co₃(CH₃COO)₂(H₂O)₁₀} unit, thereby inducing the construction of a 12‐connected framework. To the best of our knowledge, compound 3 contains the largest‐ever number of cobalt ions in a {P₈W₄₈}‐based polyoxometalate when counterions are taken into account and the {P₈W₄₈} unit shows the highest number of connections thanks to the carboxyl bridges. The UV/Vis diffuse reflectance spectra of these powder samples indicate that the corresponding well‐defined optical absorption associated with E_g can be assessed at 2.58, 2.48, and 2.73 eV and reveal the presence of an optical band gap. The photocatalytic H₂ evolution activities of these {P₈W₄₈}‐based compounds are evaluated.     

Syntheses and crystal structures of heterometallic complexes [{Cu(en)2}2{Cu(en)2(NH3)}{M4Te4(CN)12}]·5H2O (M = Mo,W)

Evaporation of aqueous ammonia solutions of K₇[Mo₄Te₄(CN)₁₂]·12H₂O or K₆[W₄Te₄(CN)₁₂]·5H₂O, copper(ii) chloride, and ethylenediamine afforded the isostructural heterometallic complexes [{Cu(en)₂}₂{Cu(en)₂(NH₃)}{M₄Te₄(CN)₁₂}]·5H₂O (M = Mo or W), which were characterized by IR and ESR spectroscopy and X-ray diffraction analysis.     

{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20]36-: a molecular quantum spin icosidodecahedron

Self-assembly of aqueous solutions of molybdate and vanadate under reducing, mildly acidic conditions results in a polyoxomolybdate-based {Mo72V30} cluster compound Na8K16(VO)(H2O)5[K10 subset{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20].150H2O, 1, a quantum spin-based Keplerate structure.