Intrinsic Molybdenum-Based POMOFs with Impressive Gas Adsorptions and Photochromism

Novel molybdenum(VI/V) POM-based self-constructed frameworks [Mo^VI₁₂O₂₄(μ₂-O)₁₂(trz)₆(H₂O)₆] ⋅ 6Hma ⋅ 18H₂O ( 1 , Htrz=1H-1,2,3-triazole, ma=methylamine), [Mo^VI₇O₁₄(μ₂-O)₈(trz)₅(H₂O)] ⋅ 7Hma ⋅ 5H₂O ( 2 ), Na₃[Mo^V₆O₆(μ₂-O)₉(Htrz)₃(trz)₃] ⋅ 7.5H₂O ( 3 ) and [Mo^V₈O₈(μ₂-O)₁₂(Htrz)₈] ⋅ 30H₂O ( 4 ) have been covalently decorated with tri-coordinated deprotonated/protonated 1,2,3-triazoles. Channels with an inner diameter of 7.5 Å were found in 1 , whereas a tunnel composed of stacking molecules with an inner diameter of 4.1 Å along the b-axis exists in 2 ; it is occupied by free disordered methylamines, showing selective adsorption of O₂ and CO₂ at 25 °C. Obvious downfield shifts were observed by ¹³C NMR spectroscopies for methylamines inside the confined channels in 1 and 2 . There are diversified pores in 3 and 4 , which are formed by the molecules themselves and intermolecular accumulations. Adsorption tests indicate that 3 and 4 are fine adsorption materials for CH₄ and CO₂ under low pressure that rely on the environments built by the POMs. Correspondingly, 1 and 2 display reversible photoresponsive thermochromism that is subtlety influenced by the channels. The polyoxometalate organic frameworks (POMOFs) with multiple functional adsorptions are easy to assemble. Their photo-/thermoresponse properties offer a new pathway for the self-constructions of one-off hybrid materials that possess the good properties of both POMs and MOFs.     

A High-Nuclear Isopolymolybdate Cluster Assembled with an Anionic [{Mo24O48(OMe)32}]8− and Two Charge-Neutral [{Mo24O52(OMe)28}] Cages

We synthesized a high-nuclear isopolymolybdate cluster (n-Bu₄N)₆H₂[{Mo₂₄O₄₈(OMe)₃₂}{Mo₂₄O₅₂(OMe)₂₈}₂] ⋅ 25H₂O ⋅ 6CH₃CN (1) by using [Mo₆O₁₉]²⁻ as the base precursor. Crystallographic characterization shows the cluster is composed of an anionic [{Mo₂₄O₄₈(OMe)₃₂}]⁸⁻ cage and two charge-neutral [{Mo₂₄O₅₂(OMe)₂₈}] cages. Supported by the electrospray ionization mass spectrometry study, the polyoxoanion structural unit [Mo₂₄O₄₈(CH₃O)₂₇]³⁻ demonstrates strong stability in acetonitrile solution. Moreover, 1 exhibits good proton conductivity of 1.79×10⁻³ S cm⁻¹ at 358 K and 98 % relative humidity.     

Experimental and Computational Studies on Quadruply Bonded Dimolybdenum Complexes with Terminal and Bridging Hydride Ligands

This contribution focuses on complex [Mo₂(H)₂(μ-Ad^Dipp2)₂] ( 1 ) and tetrahydrofuran and pyridine adducts [Mo₂(H)₂(μ-Ad^Dipp2)₂(L)₂] ( 1⋅thf and 1⋅py ), which contain a trans-(H)Mo≣Mo(H) core (Ad^Dipp2=HC(NDipp₂)₂; Dipp=2,6-iPr₂C₆H₃). Computational studies provide insights into the coordination and electronic characteristics of the central trans-Mo₂H₂ unit of 1 , with four-coordinate, fourteen-electron Mo atoms and ϵ-agostic interactions with Dipp methyl groups. Small size C- and N-donors give rise to related complexes 1⋅L but only one molecule of P-donors, for example, PMe₃, can bind to 1 , causing one of the hydrides to form a three-centered, two-electron (3c-2e) Mo-H→Mo bond ( 2⋅PMe₃ ). A DFT analysis of the terminal and bridging hydride coordination to the Mo≣Mo bond is also reported, along with reactivity studies of the Mo−H bonds of these complexes. Reactions investigated include oxidation of 1⋅thf by silver triflimidate, AgNTf₂, to afford a monohydride [Mo₂(μ-H)(μ-NTf₂)(μ-Ad^Dipp2)₂] ( 4 ), with an O,O’-bridging triflimidate ligand.     

Dendritic Iron(II) Porphyrins as Models for Hemoglobin and Myoglobin: Specific Stabilization of O2 Complexes in Dendrimers with H‐Bond‐Donor Centers

Two types of dendritically functionalized iron(II) porphyrins were prepared (Scheme) and investigated in the presence of 1,2‐dimethylimidazole (1,2‐DiMeIm) as the axial ligand as model systems for T(tense)‐state hemoglobin (Hb) and myoglobin (Mb). Equilibrium O₂‐ and CO‐binding studies were performed in toluene and aqueous phosphate buffer (pH 7). UV/VIS Titrations (Fig. 4) revealed that the two dendritic receptors 1 ⋅ Fe ^II ‐1,2‐DiMeIm and 2 ⋅ Fe ^II ‐1,2‐DiMeIm (Fig. 2) with secondary amide moieties in the dendritic branching undergo reversible complexation (Fig. 5) with O₂ and CO in dry toluene. Whereas the CO affinity is similar to that measured for the natural receptors, the O₂ affinity is greatly enhanced and exceeds that of T‐state Hb by a factor of ca. 1500 (Table). The oxygenated complexes possess half‐lives of several h (Fig. 6). This remarkable stability originates from both dendritic encapsulation of the iron(II) porphyrin and formation of a H‐bond between bound O₂ and a dendritic amide NH moiety (Fig. 11). Whereas reversible CO binding was also observed in aqueous solution (Fig. 10), the oxygenated iron(II) complexes are destabilized by the presence of H₂O with respect to oxidative decay (Fig. 9), possibly as a result of the weakening of the O₂⋅⋅⋅H−N H‐bond by the competitive solvent. The comparison between the two dendrimers with amide branchings and ester derivative 3 ⋅ Fe ^II ‐1,2‐DiMeIm (Fig. 2), which lacks H‐bond donor centers in the periphery of the porphyrin, further supports the role of H‐bonding in stabilizing the O₂ complex against irreversible oxidation. All three derivatives bind CO reversibly and with similar affinity (Fig. 8) in dry toluene, but the oxygenated complex of 3 ⋅ Fe ^II ‐1,2‐DiMeIm undergoes much more rapid oxidative decomposition (Fig. 7).     

Structural Study and Solution Integrity of Dioxomolybdenum(VI) Complexes with Tridentate Schiff Base and Azole Ligands

Four new molybdenum complexes [Mo^VIO₂(L¹)(Him)] ( 1 ), [Mo^VIO₂(L¹)(3‐MepzH] ( 2 ), [Mo^VIO₂(L²)(3‐MepzH)] ( 3 ), and [(Mo^VIO₂)₂(μ‐L³)(MeOH)₂] ( 4 ) were synthesized and characterized by IR, NMR, ESI‐MS, and single‐crystal structure analysis [H₂L¹ = 2‐(salicylideneamino)‐2‐methyl‐1‐propanol, H₂L² = 2‐(3‐methoxysalicylideneamino)‐2‐methyl‐1‐propanol, H₄L³ = 1, 7‐bis(salicylidene)dihydrazide malonic acid, Him = imidazole and 3‐MepzH = 3‐methylpyrazole]. In all four structures the molybdenum atom has a distorted octahedral coordination with the three meridional donor atoms from the Schiff base di‐ or tetraanion (L^{1, 2})^2—/(L³)^4— and one oxo group occupying the sites of the equatorial plane. The other oxo group and the azole or methanol molecule occupy the apical sites. In 1—3 two centrosymmetrically related molecules form a hydrogen‐bonded pair through the (azole)N‐H···O(alkoxo) interaction. Additional crystal packing appears to be controlled mostly by π stacking between the aromatic rings of the salicyl moiety. ESI‐MS investigations reveal that the integrity of complexes 1—4 is largely retained in methanol solution. At the same time evidence is provided that di‐ to tetranuclear oligomers of formula [{Mo^VIO₂(L)}_x] and [{Mo^VIO₂(L)}_x(3‐MepzH)] with L = L¹, L², x = 2, 3, 4 are present simultaneously with 2 and 3 in methanol solution, respectively the tetranuclear species [{(Mo^VIO₂)₂(L³)}₂] with 4 .     

Controlling the Self‐Assembly of a Mixed‐Metal Mo/V–Selenite Family of Polyoxometalates

Five mixed‐metal mixed‐valence Mo/V polyoxoanions, templated by the pyramidal SeO₃^2? heteroanion have been isolated: K₁₀[Mo^VI₁₂V^V₁₀O₅₈(SeO₃)₈]?18 H₂O ( 1 ), K₇[Mo^VI₁₁V^V₅V^IV₂O₅₂(SeO₃)]?31 H₂O ( 2 ), (NH₄)₇K₃[Mo^VI₁₁V^V₅V^IV₂O₅₂(SeO₃)(Mo^V₆V^V‐ O₂₂)]?40 H₂O ( 3 ), (NH₄)₁₉K₃[Mo^VI₂₀V^V₁₂V^IV₄O₉₉(SeO₃)₁₀]?36 H₂O ( 4 ) and [Na₃(H₂O)₅{Mo_18?xV_xO₅₂(SeO₃)} {Mo_9?yV_yO₂₄(SeO₃)₄}] ( 5 ). All five compounds were characterised by single‐crystal X‐ray structure analysis, TGA, UV/Vis and FT‐IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X‐ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing η,μ and μ,μ coordination motifs. Compounds 1 and 2 were characterised in solution by using high‐resolution ESI‐MS. The ESI‐MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2? and 3? anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self‐assembly process of the mixed‐metal systems by controlling the interplay between the cation “shrink‐wrapping” effect, the non‐conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM‐based architectures.     

A new inorganic–organic hybrid: tetra­imid­azolium octa­molyb­date(VI) containing the β‐form of the [Mo8O26]4− anion

The title compound, (C₃H₅N₂)₄[β‐Mo₈O₂₆], has been prepared from imidazole octamolybdate, (C₃H₅N₂)₄[(C₃H₄N₂)₂(γ‐Mo₈O₂₆)], which was described previously. The γ→β conversion is produced in the presence of Cu(NO₃)₂·3H₂O and is reported for the first time in this work. The X‐ray structure analysis confirmed the presence of the [Mo₈O₂₆]^4? anion. The structure consists of β‐Mo₈O₂₆ polyanions and imidazolium cations. These cations are linked to the terminal and bridging O atoms of the anion by hydrogen bonds.     

Organic‐Inorganic Hybrid Supramolecular Assemblies Based on Isomers [HxAs2Mo6O26](6–x)– Clusters

The arsenomolybdates [H₂As₂Mo₆O₂₆(H₂O)] · (H₂biyb)₂ · 2H₂O ( 1 ) and [H₃As₂Mo₆O₂₆] · (H₃pt)₂ ( 2 ) [biyb = 1,4‐bis(imidazol‐1‐ylmethyl)benzene, pt = 4′‐(3′′‐pyridyl)‐2,3′:6′3′′‐terpyridine] were synthesized via hydrothermal method. The structures of the compounds were characterized by single‐crystal X‐ray diffraction analyses, elemental analyses, IR spectroscopy, and TG analysis. Compounds 1 and 2 exhibit two isomeric forms of [H_xAs₂Mo₆O₂₆]^(6–x)–. The structure of 1 is constructed from the B‐type [H₂As₂Mo₆O₂₆(H₂O)]^4– polyanions and free biyb ligands via weak interactions to form 3D supramolecular framework with a {3 · 4 · 5³ · 6}{3 · 4³ · 5²}{3 · 5 · 6}²{3 · 5²}² topology structure. In compound 2 , the A‐type [H₃As₂Mo₆O₂₆]^3– clusters are surrounded by pt ligands through hydrogen bond interactions forming 3D supramolecular framework with a {4³ · 6³}²{4⁶ · 6⁶ · 8³} topology structure. The electrochemical behaviors, electrocatalytic and photocatalytic activities of 1 and 2 are detected.     

A Signal‐Amplified Electrochemical Immunosensor Based on Prussian Blue and Pt Hollow Nanospheres as Matrix

Through electrodepositing Prussian blue (PB) and chitosan (CS), then casting Pt hollow nanospheres (HN‐Pt) and assembling CA19‐9 antibody on the electrode surface, an immunosensor was achieved. A new signal amplification strategy based on PB and HN‐Pt toward the electrocatalytic reduction of H₂O₂ was employed when performing the determination. The resulting immunosensor showed a high sensitivity, broad linear response to carbohydrate antigen 19‐9 (CA19‐9) in two ranges from 0.5 to 30 and 30 to 240 U mL^?1 with a low detection limit of 0.13 U mL^?1 (S/N=3). Moreover, it displayed good reproducibility and stability, and would be potentially attractive for clinical immunoassay of CA19‐9.     

Molecular and Silica‐Supported Mo and W d0 Imido‐Methoxybenzylidene Complexes: Structure and Metathesis Activity

5‐Coordinated methoxybenzylidene complexes M(=NAr)(=CH?C₆H₄?o‐OMe)(O^tBu_F3)₂ (Ar=2,6‐ⁱPr₂C₆H₃; ^tBu_F3=CMe₂(CF₃)) of Mo ( 1m_Mo ) and W ( 1m_W ) were synthesized by cross‐metathesis from the corresponding neophylidene/neopentylidene precursors and o‐methoxystyrene. 1m_Mo and 1m_W were grafted onto the surface of silica partially dehydroxylated at 700 °C to give well‐defined silica‐supported alkylidenes (≡SiO)M(=NAr)(=CH?C₆H₄?o‐OMe)(O^tBu_F3) (M=Mo ( 1_Mo ), W ( 1_W )). Supported methoxybenzylidene complexes were tested in metathesis of cis‐4‐nonene, 1‐nonene, and ethyl oleate, and compared to their molecular precursors and supported classical analogs (≡SiO)M(=NAr)(=CHCMe₂R)(O^tBu_F3) (M=Mo, R=Ph ( 2_Mo ), M=W, R=Me ( 2_W )). Both grafted complexes 1_Mo and 1_W show significantly better performance as compared to their molecular precursors 1m_Mo and 1m_W but are less efficient than the classical 4‐coordinated alkylidenes 2_Mo and 2_W . Noteworthy, both 1_Mo and 1_W can reach equilibrium conversion in metathesis of cis‐4‐nonene at catalyst loadings as low as 50 ppm.     

Characterization of tetra,dodeca and tetradeca MoV polyoxometalate wheels structured by etidronate ligands

The reactivity of the [Mo^V₂O₄]²⁺ dinuclear unit with the [O₃P(C(CH₃)(OH))PO₃]^4? etidronate ligand has been investigated. Three complexes have been isolated and characterized by IR spectroscopy, elemental analysis and single crystal X-Ray diffraction studies. Structural determination of the tetranuclear compound (CN₃H₆)₆[(Mo^V₂O₄)₂(O₃P(C(CH₃)O)PO₃)₂]·12H₂O (1) revealed that the hydroxo group of the etidronate ligand can be deprotonated in presence of Mo^V even in acidic media. It follows that its coordination mode thus differs from that of the methylenediphosphonate ligand [O₃P(CH₂)PO3]4?, which reactivity with Mo^V has been previously widely studied. In contrast, no such deprotonation of the hydroxo group is observed in the (NH₄)₁₈[(Mo^V₂O₄)₆(OH)₆(O₃P(C(CH₃)(OH))PO₃)₆]·35H₂O complex 2. This species contains a dodecanuclear core analogous to the one previously found in the [(Mo^V₂O₄)₆(OH)₆(O₃PCH₂PO₃)₆]^18? methylenediphosphonato polyanion. In 2, six interconnected {(Mo^V₂O₄)(O₃P(C(CH₃)(OH))PO₃)} units form a cyclohexane-like ring in a chair conformation. In the (CN₃H₆)₁₈Na₃[(Mo^V₂O₄)₇(O₃P(C(CH₃)(OH))PO₃)₇(CH₃COO)₇]·5CH₃COONa 52H₂O compound 3, seven {(Mo^V₂O₄)(O₃P(C(CH₃)(OH))PO₃)(CH₃COO)} units are connected, forming an almost planar tetradecanuclear wheel. This compound represents the largest homometallic Mo^V polyoxometalate cyclic system reported to date. Finally, ³¹P NMR studies revealed that only complex 1 is stable in aqueous solution.     

Substituent Effect to Fine-Tune Energy Levels of Atom-Precise [MoOS3]2− Modified Copper(I) Thiolate Clusters Boosting Recyclable Photocatalysis

The propulsion of photocatalytic hydrogen (H₂) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS₃]²⁻ unit is introduced into the Cu^I clusters to form a series of atomically-precise Mo^VI−Cu^I bimetallic clusters of [Cu₆(MoOS₃)₂(C₆H₅(CH₂)S)₂(P(C₆H₄−R)₃)₄] ⋅ xCH₃CN (R=H, CH₃, or F), which show high photocatalytic H₂ evolution activities and excellent stability. By electron push-pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these Mo^VI−Cu^I clusters can be finely tuned, promoting the resultant visible-light-driven H₂ evolution performance. Furthermore, Mo^VI−Cu^I clusters loaded onto the surface of magnetic Fe₃O₄ carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster-based catalyst. This work not only highlights a competitively universal approach on the design of high-efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy.     

Catalytic Spectrophotometric Determination of Titanium(IV) Using Methylene Blue‐Ascorbic Acid Redox Reaction

A highly selective and sensitive catalytic method for the determination of trace amounts of titanium(IV) was developed. The method is based on the catalytic effect of titanium(IV) on the methylene blue‐ascorbic acid redox reaction. The reaction was followed spectrophotometrically by measuring the change in absorbance of methylene blue at 665 nm, 5 minutes after the initiation of the reaction. In this study experimental parameters were optimized and the effect of the presence of various cations and some anions on the determination of titanium(IV) was examined. The calibration graph was linear in the range of 3‐25 ng mL^?1 of titanium(IV). The relative standard deviation for the determination of 10 and 20 ng mL^?1 of titanium(IV) were 2.64% and 1.51%, respectively (n = 8). The detection limit calculated from three times of standard deviation of blank 3S_b was 0.6 ng mL^?1. The method was successfully applied to the determination of titanium(IV) in tap water and ore samples.     

Synthesis and Crystal Structure of Two New Molydenum(V) Pyrophosphate Complexes

Two new reduced molybdenum pyrophosphates, Na₂₈[Na₂{(Mo₂O₄)₁₀(P₂O₇)₁₀(HCOO)₁₀}]·108H₂O ( 1 ) and Na₂₂(H₃O)₂[Na₄{(Mo₂O₄)₁₀(P₂O₇)₁₀(CH₃COO)₈(H₂O)₄}]·91H₂O ( 2 ) have been synthesized and characterized by single‐crystal X‐ray diffraction. Red crystals of 1 are triclinic, space group , with a = 17.946(4) Å, b = 18.118(4) Å, c = 21.579(4) Å, α = 114.47(3)°, β = 93.54(3)°, γ = 114.39(3)° and V = 5581.8(19) ų, and orange crystals of 2 are monoclinic, space group P2₁/n, with a = 21.467(4) Å, b = 23.146(5) Å, c = 24.069(5) Å, β = 101.76(3)° and V = 11708(4) ų. They are both constructed by Mo^V dimers ({Mo₂O₄(O_P)₄(HCOO)} in 1 , {Mo₂O₄(O_P)₄(CH₃COO)} and {Mo₂O₄(O_P)₄(H₂O)₂} in 2 ) and pyrophosphoric groups. Their structures can be described as two interconnected nonequivalent wheels which are approximately perpendicular, delimiting a large cavity. The larger wheel contains six Mo^V dimers, while the smaller one has four dimers.     

Molybdenum Bisphosphonates with Cr(III) or Mn(III) Ions

The synthesis of Mo^VI bisphosphonates (BPs) complexes in the presence of a heterometallic element has been studied. Two different BPs have been used, the alendronate ligand, [O₃PC(C₃H₆NH₃)(O)PO₃]^4? (Ale) and a new BP derivative with a pyridine ring linked to the amino group, [O₃PC(C₃H₆NH₂CH₂C₅H₄N)(O)PO₃]^4? (AlePy). Three compounds have been isolated, a tetranuclear Mo^VI complex with Cr^III ions, (NH₄)₅[(Mo₂O₆)₂(O₃PC(C₃H₆NH₃)(O)PO₃)₂Cr]·11H₂O (Mo₄(Ale)₂Cr), its Mn^III analogue, (NH₄)_4.5Na_0.5[(Mo₂O₆)₂(O₃PC(C₃H₆NH₃)(O)PO₃)₂Mn]·9H₂O (Mo₄(Ale)₂Mn), and a cocrystal of two polyoxomolybdates, (NH₄)₁₀Na₃[(Mo₂O₆)₂(O₃PC(C₃H₆NH₂CH₂C₅H₄N)(O)PO₃)₂Cr]₂[CrMo₆(OH)₆O₁₈]·37H₂O ([Mo₄(AlePy)₂Cr]₂[CrMo₆]). In this latter compound an Anderson-type POM [CrMo₆(OH)₆O₁₈]^3? is sandwiched between two tetranuclear Mo^VI complexes with AlePy ligands. The protonated triply bridging oxygen atoms bound to the central Cr^III ion of the Anderson anion develop strong hydrogen bonding interactions with the oxygen atoms of the bisphosphonate complexes. The UV–Vis spectra confirm the coexistence in solution of both POMs. Cyclic voltammetry experiments have been performed, showing the reduction of the Mo centers. In strong contrast with the reported Mo^VI BP systems, the presence of trivalent cations in close proximity to the Mo^VI centers dramatically impact the potential solid-state photochromic properties of these compounds.     

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.     

Dimeric copper(II) trimethylsilyl­acetate adducts with pyridine, 2‐­methylpyridine, 3‐methylpyridine and quinoline,and a polymeric copper(II) trimethylsilylacetate

In the crystals of bis(pyridine‐N)tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₅H₅N)₂], (I), the dinuclear Cu^II complexes have cage structures with Cu?Cu distances of 2.632 (1) and 2.635 (1) Å. In the crystals of bis(2‐­methylpyridine‐N)tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₆H₇N)₂], (II), bis­(3‐methylpyridine‐N)tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₆H₇N)₂], (III), and bis(quinoline‐N)­tetrakis(μ‐­trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₉H₇N)₂], (IV), the centrosymmetric dinuclear Cu^II complexes have a cage structure with Cu?Cu distances of 2.664 (1), 2.638 (3) and 2.665 (1) Å, respectively. In the crystals of catena‐poly­[tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II)], [Cu₂(C₅H₁₁O₂Si)₄]_n, (V), the dinuclear Cu^II units of a cage structure are linked by the cyclic Cu—O bonds at the apical positions to form a linear chain by use of a glide translation.     

Hexa‐ and Dodecanuclear Polyoxomolybdate Cyclic Compounds: Application toward the Facile Synthesis of Nanoparticles and Film Electrodeposition

Two new compounds based on O₃PCH₂PO₃^4? ligands and {Mo^V₂O₄} dimeric units have been synthesized and structurally characterized. The dodecanuclear Mo^V polyoxomolybdate species in (NH₄)₁₈[(Mo^V₂O₄)₆(OH)₆(O₃PCH₂PO₃)₆]?33 H₂O ( 1 ) is a cyclohexane‐like ring in a chair conformation with pseudo S₆ symmetry. In the solid state, the wheels align side by side, thus delimiting large rectangular voids. The hexanuclear anion in Na₈[(Mo^V₂O₄)₃(O₃PCH₂PO₃)₃(CH₃AsO₃)]? 19 H₂O ( 2 ) has a triangular framework and encapsulates a methylarsenato ligand. ³¹P NMR spectroscopic analysis revealed the stability of 2 in various aqueous media, whereas the stability of 1 depends on the nature of the cations present in solution. It has been evidenced that the transformation of 1 into 2 occurs in the presence of CH₃AsO₃^2? ions. This behavior shows that 1 can be used as a new precursor for the synthesis of Mo^V/diphosphonate systems. The two complexes were very efficient both as reductants of Pt and Pd metallic salts and as capping agents for the resulting Pt⁰ and Pd⁰ nanoparticles. The size of the obtained nanoparticles depends both on the nature of the polyoxometalate (POM; i.e., 1 or 2 ) and on the [metallic salt]/[POM] ratio. In all cases, X‐ray photoelectron spectroscopy (XPS) measurements have revealed the presence of Mo^VI species that stabilize the nanoparticles and the absence of Mo^V moieties. Diffuse‐reflectance FTIR spectra of the Pt nanoparticles show that the capping Mo^VI POMs are identical for both systems and contain the diphosphonato ligand. The colloidal solutions do not show any precipitate and the nanoparticles remain well‐dispersed for several months. The electrochemical reduction of Mo^V species was studied for 2 . Cyclic voltammetry alone and electrochemical quartz crystal microbalance coupled with cyclic voltammetry show the deposition of a film on the electrode surface during this reduction.     

A new class of 30-molybdo complexes: Formation,structure and electrochemical properties of bisselenitopyrophosphatotriacontamolybdate, [(SeO3)2(P2O7)Mo30O90]8−, and bispyrophosphatotriacontamolybdate, [(P2O7)2Mo30O90]8−

The tetrapropylammonium (Pr₄N⁺) salt of [(SeO₃)₂(P₂O₇)Mo₃₀O₉₀]^8? was prepared from a 75 mM Mo^VI–2.8 mM P₂O₇^4?–5.6 mM SeO₃^2?–0.95 M HCl–60% (v/v) CH₃CN system, where [(P₂O₇)Mo₁₈O₅₄]^4? and [H₆(SeO₃)₂Mo₁₅O₄₈]^4? are first formed, then being spontaneously fused into [(SeO₃)₂(P₂O₇)Mo₃₀O₉₀]^8?. The [(SeO₃)₂(P₂O₇)Mo₃₀O₉₀]^8? anion may be isotypic with [(HPO₃)₂(P₂O₇)Mo₃₀O₉₀]^8?, in which each side of a (P₂O₇)Mo₁₂O₄₂ fragment is capped by a B-type (HPO₃)Mo₉O₂₄ unit derived from [H₆(HPO₃)₂Mo₁₅O₄₈]^4?. [(XO₃)₂(P₂O₇)Mo₃₀O₉₀]^8? (X = HP, Se) have the same type of 30-molybdo framework as [(P₂O₇)₂Mo₃₀O₉₀]^8?, previously isolated by Koltz. These three 30-molybdo complexes with the same ionic charge of ?8 constitute a new class of polyoxometallates and have common properties of undergoing a two-electron reduction in the absence of H⁺.     

An organic‐inorganic heterogeneous catalyst based on Keplerate polyoxometalates for oxidation of dibenzothiophene derivatives with Hydrogen peroxide

An organic‐inorganic material (NH₄)₂(MimAM)₄₀[Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂] have been synthesized by reacting [(NH₄)₄₂[Mo^VI₇₂ Mo^V₆₀O₃₇₂(CH₃COO)₃₀(H₂O)₇₂] with the ionic liquid 3‐Aminoethyl‐1‐methylimidazolium bromide. The catalyst showed remarkably a high catalytic performance in the oxidation of dibenzothiophene (DBT) derivatives with H₂O₂ 35% as a safe and green oxidant. The main parameters affecting the process including catalyst, acid additive, hydrogen peroxide amounts and temperature have been investigated in detail. Sulfur removal of DBT in n‐heptane reached to 98.3% yield at 40 °C using 2.5 mmol H₂O₂ and 100 mg of (NH₄)₂(MimAM)₄₀[Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂] after 90 min. Under the optimal conditions, BT (benzothiophene), DBT (dibenzothiophene) and 4,6‐DMDBT (4,6‐dimethyl‐dibenzothiophene) achieved high desulfurization efficiency. Our results showed that the reactivity order of different model sulfur compounds are thiophene <4,6‐dimethyl dibenzothiophene< dibenzothiophene. The catalysts could be easily separated from the reaction solution by simple filtration and recycled for several times without loss of activity.