New Series of Porous Ionic Crystals Constructed from Various Polyoxometalate Anions and Macrocations: Syntheses,Crystal Structures,and Comparison with Diverse Spatial Arrangement

A new series of ionic crystals, KH₂[Cr₃O(OOCCH₃)₆(H₂O)₃][α‐SiMo₁₂O₄₀] · 11 H₂O ( 1 ), KH₂[Cr₃O(OOCCH₃)₆(H₂O)₃][α‐SiW₁₂O₄₀]μ·μ11H₂O ( 2 ), K₂[Cr₃O(OOCCH₃)₆ (H₂O)₃][α‐PW₁₂O₄₀]μ· 17H₂O ( 3 ), Na[Cr₃O(OOCCH₃)₆(H₂O)₃]₂[α‐PMo₁₂O₄₀] · 11H₂O ( 4 ), H₅[Cr₃O(OOCCH₃)₆(H₂O)₃] [α‐P₂Mo₁₈O₆₂] · 10H₂O ( 5 ) based on a polyoxometalate building block with a macrocation, have been synthesized in aqueous solution and structurally characterized by single‐crystal X‐ray diffraction, IR spectra, elemental analysis, thermogravimetric analysis (TGA). The polyanions and macrocations stacked alternately through hydrogen bonds as well as electrostatic interactions to constitute a novel porous microstructure. In the crystal structures of 1 , 2 , and 3 , oppositely charged cluster ions stacked alternately to form one‐dimensional channels. Compound 4 exhibits an unique structure that six macrocation pillars packed along the a‐axis to form a straight 1D channel, in which accommodates a polyoxometalate pillar. In compound 5 , six α‐Dawson‐type polyoxometalate pillars stacked on top of each other along the a‐axis to form a straight 1D channel, which houses a macrocation pillar. The magnetic investigation on compounds 1 and 5 shows a typical antiferromagnetic interaction of the macrocation [Cr₃O(OOCCH₃)₆(H₂O)₃]⁺, almost independent from the presence of polyoxometalate anions.     

Synthesis,structure and properties of rare earth substituted germanotungstates: Pr/[α-GeW11O39]

Two new polyoxometalate compounds based on the lacunary Keggin anion [α-GeW₁₁O₃₉]^8? and the rare earth cation Pr^III, [(CH₃)₄N]_2.25H_1.25[Pr_1.5(GeW₁₁O₃₉)(H₂O)_5.75] · 1.25H₂O (1) and [Pr_0.5(H₂O)_2.25]H_0.5[Pr₂(GeW₁₁O₃₉)(DMSO)₂(H₂O)₈] · 5.75H₂O (2), have been synthesized and characterized by elemental analysis, inductively coupled plasma (ICP) analysis, IR and UV spectroscopy, and single-crystal X-ray diffraction. The solid-state structure of 1 consists of one-dimensional zig-zag chains built of [α-GeW₁₁O₃₉]^8? anions connected by Pr³⁺. In 2, DMSO (DMSO = dimethyl sulfoxide) leads to a double-parallel chainlike structure constructed by two linear wires {[Pr(GeW₁₁O₃₉)(DMSO)(H₂O)₂]^5?} _n linked by Pr³⁺ coordination cations.     

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

A mononuclear‐cobalt(II)‐substituted silicotungstate, K₁₀[Co(H₂O)₂(γ‐SiW₁₀O₃₅)₂] ? 23 H₂O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated [Ru(bpy)₃]³⁺ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s^?1), and quantum yield (Φ_QY; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely [Ni(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 2 ) and [Mn(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the [Ru(bpy)₃]²⁺/visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., [Co₄(H₂O)₂(α‐PW₉O₃₄)₂]^10? (Co₄‐POM) and [Co^IIICo^II(H₂O)W₁₁O₃₉]^7? (Co₂‐POM)) under optimum conditions.     

Synthesis and characterisation of novel ruthenium multi-substituted polyoxometalates: α,β-[SiW9O37Ru4(H2O)3Cl3]

Novel ruthenium multi-substituted polyoxometalate compounds of general formulae K₆Na[SiW₉O₃₇Ru^III₄(H₂O)₃Cl₃]·nH₂O (α- and β-SiW₉O₃₄ isomers) were synthesised via the reactions of the trilacunary Keggin α- and β-[SiW₉O₃₄]¹⁰⁻ anions with RuCl₃ in aqueous solution. Characterisation was performed by analytical, spectroscopic, magnetic, and electrochemical techniques. The results are in accordance with the new polyoxometalates having the trivacant Keggin anion (α or β isomer) linked to a cubane-type Ru₄O₄ cluster. The co-ordination sphere of ruthenium is completed with water molecules and chloride anions. Magnetic measurements showed that the majority of the molecules have the Ru ions cluster in a compensated configuration constrained to an antiferromagnetic alignment at very low temperature and following a Curie-Weiss like behaviour. For both isomers, cyclic voltammetry revealed quasi-reversible redox processes at the ruthenium centres, namely Ru^IV/III and Ru^III/II, which were found to be pH dependent. The novel polyoxotungstates incorporate the highest content of ruthenium (W:Ru = 2.25:1) ever reported for Keggin-, Dawson or sandwich-type transition metal-substituted polyoxometalates and may find promising applications as oxidative catalysts.     

Determination of kinetic parameters of inorganic metalporphyrins

The thermal properties of four heteropoly complexes α-K₃H₃[SiW₁₁Ni(H₂O)O₃₉]·11.5H₂O (I), α-K₃H₂[SiW₁₁Fe(H₂O)O₃₉]·9H₂O (II), α-[(C₄H₉)₄N]_3.5H_1.5[SiW₁₁Fe(H₂O)O₃₉]·4.5H₂O (III) and α-[(C₄H₉)₄N]_3.5H_2.5[SiW₁₁Cu(H₂O)O₃₉]·6H₂O (IV) were studied by means of TG, DTA and DSC. The activation energy and reaction order of the thermal decomposition reaction of these complexes have been calculated.

---

Zusammenfassung Mittels TG, DTA und DSC wurden die thermischen Eigenschaften der vier heteropolaren Komplexe α-K₃H₃[SiW₁₁Ni(H₂O)O₃₉]·11.5H₂O (I), α-K₃H₂[SiW₁₁Fe(H₂O)O₃₉]·9H₂O (II), α-[(C₄H₉)₄N]_3.5H_1,5[SiW₁₁Fe(H₂O)O₃₉]·4.5H₂O (III) und α-[(C₄H₉)₄N]_3.5H_2,5 [SiW₁₁Cu(H₂O)O₃₉]·6H₂O (IV) untersucht. Die Aktivierungsenergie und Reaktionsordnung der thermischen Zersetzungsreaktion dieser Komplexe wurde berechnet.

     

Ionic crystals based on Keggin anion and mixed-valent diruthenium tetracetate: [Ru2(CH3COO)4(H2O)2]2[HnXW12O40]·[Ru2(CH3COO)4(H2O)Cl]·12H2O (X = B,Si, Ge)

Three new ionic crystals based on Keggin anion and mixed-valent diruthenium tetracetate, [Ru₂(CH₃CO₂)₄(H₂O)₂]₂[H_nXW₁₂O₄₀]·[Ru₂(CH₃CO₂)₄(H₂O)Cl]·12H₂O {X = B, n = 3 (1); X = Si, n = 2 (2); X = Ge, n = 2 (3)}, have been prepared in acidic aqueous solution at about pH 3.0 by reaction of K₄BW₁₂O₄₀·mH₂O, K₈SiW₁₁O₃₉·mH₂O and K₈GeW₁₁O₃₉·mH₂O with diruthenium tetracetate Ru₂(CH₃COO)₄Cl, respectively, and their structures were determined by X-Ray diffraction analysis. They are isostructural structure with the ratio of heteropolytungstate anion, Ru₂(CH₃CO₂)₄⁺ cation and neutral molecular Ru₂(CH₃CO₂)₄Cl of 1:2:1. The cyclic voltammetry in 0.5 M KNO₃ aqueous solution at pH 3.0 show the respective electrochemical behaviors of the W-centers and Ru₂-centers for these three complexes. Magnetic data analysis shows that diruthenium units display the ground state electronic configuration π*²δ* with large positive D value.     

Stabilization of High‐Valence Ruthenium with Silicotungstate Ligands: Preparation,Structural Characterization,and Redox Studies of Ruthenium(III)‐Substituted α‐Keggin‐Type Silicotungstates with Pyridine Ligands, [SiW11O39RuIII(Py)]5−

Ruthenium(III)‐substituted α‐Keggin‐type silicotungstates with pyridine‐based ligands, [SiW₁₁O₃₉Ru^III(Py)]^5?, (Py: pyridine ( 1 ), 4‐pyridine‐carboxylic acid ( 2 ), 4,4′‐bipyridine ( 3 ), 4‐pyridine‐acetamide ( 4 ), and 4‐pyridine‐methanol ( 5 )) were prepared by reacting [SiW₁₁O₃₉Ru^III(H₂O)]^5? with the pyridine derivatives in water at 80 °C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and ¹H NMR spectroscopy, elemental analysis, titration, and X‐ray absorption near‐edge structure (XANES) analysis (Ru K‐edge and L₃‐edge). Single‐crystal X‐ray analysis of compounds 2 , 3 , and 4 revealed that Ru^III was incorporated in the α‐Keggin framework and was coordinated by pyridine derivatives through a Ru? N bond. In the solid state, compounds 2 and 3 formed a dimer through π? π interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated Ru^III–Py was reversibly oxidized into the Ru^IV–Py derivative and reduced into the Ru^II–Py derivative.     

Investigation of the state of palladium in the potassium palladium-11-tungstosilicate/alumina system by diffuse-reflectance IR spectroscopy

The influence of redox treatments on the state of palladium in the K₆[SiW₁₁PdO₃₉]·11H₂O/γ-Al₂O₃ system was investigated by diffuse-reflectance IR (DRIFT) spectroscopy using CO as a probe molecule. The K₆[SiW₁₁PdO₃₉]·11H₂O heteropoly-compound (HPC) and starting γ-Al₂O₃ support were studied for comparison. It was shown that palladium is present in HPC mainly in the form of Pd²⁺ ions. Treatment of HPC in an H₂ flow results in complete reduction of palladium to Pd⁰. The HPC is unstable in redox cycles at temperatures above 373 K. When the HPC was supported on alumina, the Keggin units were stabilized on the support surface and Pd⁺ formed in the oxidized sample. The supported K₆[SiW₁₁PdO₃₉]·11H₂O/γ-Al₂O₃ catalyst displays higher thermal stability and does not decompose during redox treatments at temperatures up to 723 K. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1271–1275. July, 1999.     

pH-dependent assembly of saturated to dilacunary Keggin-based silicotungstate: [Cu(en)2(H2O)][H2en]{γ-SiW10O36[Cu(en)2(H2O)]2}·7.5H2O

By controlling the pH of the reaction system, a dilacunary γ-Keggin silicotungstate [Cu(en)₂(H₂O)][H₂en]{γ-SiW₁₀O₃₆[Cu(en)₂(H₂O)]₂}·7.5H₂O (1) (en?=?ethylenediamine) has been hydrothermally synthesized by the reaction of CuCl₂ with α-H₄SiW₁₂O₄₀ and characterized by IR spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. The product is prepared in the pH range 7.9–8.2, which reveals that pH plays a key role in the assembly of saturated α-H₄SiW₁₂O₄₀ to dilacunary [γ-SiW₁₀O₃₆]^8? polyoxometalate. The polyoxoanion {γ-SiW₁₀O₃₆[Cu(en)₂(H₂O)]₂]}^4? of 1 presents a rare [γ-SiW₁₀O₃₆]^8?-retaining structure, in which two lacunary sites of [γ-SiW₁₀O₃₆]^8? are unoccupied, meanwhile, two [Cu(en)₂(H₂O)]²⁺ groups are grafted on either side of the [γ-SiW₁₀O₃₆]^8? unit by Cu–O–W bond.     

A kinetic study on the iron(III)-promoted aquation of [Cr(C2O4)2(picolinato)]2− and [Cr(C2O4)2(2-pyridineacetato)]2− complexes

Two [Cr(C₂O₄)₂(AB)]^2– type complexes, obtained from the reaction of cis-[Cr(C₂O₄)₂(H₂O)₂]^– with the AB ligand, [AB = picolinic (pyac) or 2-pyridine-ethanoic acid (pyeac) anions], were converted into [Cr(C₂O₄)(pyac)(H₂O)₂]⁰ and [Cr(C₂O₄)(pyeac)(H₂O)₂]⁰ compounds, respectively via Fe^III-induced substitution of the oxalato ligand. The aquation products were separated chromatographically and their spectral characteristics and acid dissociation constants determined. The kinetics of the oxalato ligand substitution were studied with a 10–40 fold excess of Fe^III over [Cr^III] at [H⁺] = 0.2 M and at constant ionic strength 1.0 M (Na⁺, H⁺, Fe³⁺, ClO^– ₄). The reaction rate law is of the form: r = k _obs[Cr^III], where k _obs = kQ[Fe^III]/(1 + Q[Fe^III]). The first-order rate constants (k), preequilibria quotients (Q) and activation parameters derived from the k values have been determined. The reaction mechanism is discussed in terms of a Lewis acid catalyzed (induced) ligand substitution.     

Transition metal substituted polyoxometalates supported on amine-functionalized silica

A series of transition metal substituted polyoxometalates (POM) have been anchored to propylamine-functionalized mesoporous silica (silicaNH₂). These include V, Co and Mn Keggin-type anions such as [PMo₁₀V₂O₄₀]⁵⁻ and [PMo₁₁VO₄₀]⁴⁻, or [SiW₁₁Co^II(H₂O)O₃₉]⁶⁻ and [SiW₁₁Mn^III(H₂O)O₃₉]⁵⁻, and sandwich-type anions, [(PW₉O₃₄)₂ Co ₄ ^II (H₂O)₂]¹⁰⁻ and [(PW₉O₃₄)₂Mn ₄ ^II (H₂O)₂]¹⁰⁻. Experiments at different initial pH_i of aqueous suspension of silica were performed for the Co and Mn substituted Keggin anions. The novel silicaNH₂-POM materials having between 12–17% (w/w) of polyoxometalate were characterized by elemental analysis, solid-state ²⁹Si, ¹³C and ³¹P n.m.r., diffuse reflectance spectroscopy, FTIR spectroscopy, thermal analyses, and BET surface area measurements. The elemental analyses and spectroscopic results pointed to the integrity of POM structures after immobilization on the silica support while the latter one showed a slight decrease of BET surface area. Results of the visible diffuse reflectance spectroscopy for the Co-substituted Keggin anion revealed the coordination of cobalt centers in the cluster with the nitrogen atom of amine groups in modified silica at pH_i ≥ 5.5 or the electrostatic bonding between polyoxoanion and protonated C₃H₆NH ₃ ⁺ group at pH_i = 3.5. For the Co-substituted sandwich anion, external Co centres of the polyoxoanion have coordinated with the amine groups of modified silica under the experimental conditions used. ³¹P MAS n.m.r. showed a shifting of phosphorus atom resonances in H₅[PMo₁₀V₂O₄₀] and H₄[PMo₁₁VO₄₀] to a single resonance at ca. − 4.1 ppm (Δv _1/2 ~ 70 Hz) when these POM were immobilized on the functionalized silica under weak acidic conditions (pH 3), evidencing electrostatic interaction of POM clusters with the C₃H₆NH ₃ ⁺ groups.     

A low dielectric constant polyimide/polyoxometalate composite

A silane‐modified mono‐lacunary Keggin‐type polyoxometalate (POM), (Bu₄N)₄[SiW₁₁O₃₉{(CH₂?CH? Si)₂O}] (SiW₁₁? CH?CH₂), was obtained by reaction of vinyltrimethoxysilane with K₈(SiW₁₁O₃₉) in acidic MeCN/H₂O mixed solutions. Then, the modified polyoxometalate was physically blended with the pyromellitic dianhydride (PMDA)‐4,4′‐oxydianiline (ODA) poly(amic acid) and the blends were thermally imidized to form polyimide/ polyoxometalate composites. The X‐ray diffraction (XRD) analysis indicates that the polyoxometalate clusters cannot form crystalline structures in the composite, suggesting that the blending leads to improved compatibility between the polymer matrix and the modified polyoxometalate. The EDS (W‐mapping) studies on the composite films reveal that the polyoxometalate clusters are well dispersed in the polyimide matrix. The physical incorporation of modified POM into polyimide remarkably reduced the dielectric constant of the latter from 3.29 to 2.05 when 20 wt% of SiW₁₁? CH?CH₂ was used. Besides, the addition of the modified POM into polyimide increased the storage modulus of polyimide without severely affecting its thermal properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Reactions of chromium(III) complexes with ferricyanide. Magnetism of K2[Cr(salen)(H2O)][Fe(CN)6]·H2O and the crystal structure of [trans-Cr(tn)2Cl2]3[Fe(CN)6]·6H2O [salen2− = N,N′-ethylenebis(salicylideneaminato) dianion,tn = 1,3-diaminopropane]

Two Cr^III–Fe^III complexes, K₂[Cr(salen)(H₂O)][Fe(CN)₆]·H₂O (1) and [trans-Cr(tn)₂Cl₂]₃[Fe(CN)₆]·6H₂O (2), have been prepared. Crystal structure determination shows that complex (2) possesses an ionic salt structure. General physical measurements and magnetic studies indicate that (1) assumes a cyanide-bridged dinuclear structure, and that the Cr^III–Fe^III magnetic coupling through the cyanide bridge is antiferromagnetic, which can be rationalized by the overlap of magnetic orbitals of the same symmetry.     

Novel channeled compound based on Cr(III) trinuclear complex and polyoxometalate aimed for heterogeneous catalysis: synthesis and structure

Keggin-type polyoxometalate [SiW₁₂O₄₀]^4-, and Cr(III) trinuclear cation [Cr₃O (OOCH)₆(H₂O)₃]⁺, assembled in the presence of K⁺ to form a novel complex, K₃[Cr₃O(OOCH)₆ (H₂O)₃]SiW₁₂O₄₀2H₂O (1). The structure was confirmed by single crystal X-ray analysis, FT-IR and diffuse reflectance UV-vis spectroscopy. The investigation with FT-IR, and diffuse reflectance UV-vis measurements revealed that 1 was stable up to 200°C. It was revealed by single crystal X-ray analysis that 1 possesses a straight channel filled with water molecules, which can be removed upon heat treatment without degradation in the structure of the constituent ions.     

Structural stability index of heteropoly- and isopolyanions—IV. Application to site-vacant Keggin polyanions,mixed-type Keggin polyanions,some molybdo- and tungsto-vanadates and Jeannin-type polyanion

The theory of structural stability, being based on the number of closed loops per MO₆ octahedral unit in the polyanion-cage, has been applied to a variety of heteropoly- and isopoly-compounds with previously unreported structures. The discussion includes the prediction of the structure of lacunary Keggin heteropoly-compound, Cs₇Na₂[PW₁₀O₃₇]·8H₂O, recently obtained by Knoth and Harlow, the reinvestigation of mixed-type Keggin polyanions, [SiW₉Co₃(H₂O)₃O₃₇]^10? and [SiW₁₁CoO₃₉]^6?, recently prepared by Pope's group, the interpretation of chemical behaviours of some molybdo- and tungsto-vanadates, the structural stabilities of Jeannin-type [As₂W₂₁O₆₉(H₂O)]^6? polyanion and its related compounds, and some remarks on Weakley-type [X(W₅O₁₈)₂]^n? polyanions and Flynn-Stucky-type [X(Nb₆O₁₉)₂]^n? complexes belonging to the hybrid-complex of polyanion.     

Syntheses, structures and properties of 3D inorganic-organic hybrid frameworks constructed from lanthanide polymer and Keggin-type tungstosilicate

Inorganic-organic hybrid frameworks, namely [Ce(H₂O)₃(pdc)]₄[SiW₁₂O₄₀]·6H₂O 1, [M(H₂O)₄(pdc)]₄[SiW₁₂O₄₀]·2H₂O (M=Ce for 2a, La for 2b, Nd for 2c; H₂pdc=pyridine-2,6-dicarboxylic acid) were assembled through incorporation of Keggin-type heteropolyanion [SiW₁₂O₄₀]⁴⁻ within the voids of lanthanides-pdc network as pillars or guests under hydrothermal condition. Single-crystal X-ray analyses of these crystals reveal that compound 1 presents 3D pillar-layered framework with the [SiW₁₂O₄₀]⁴⁻ anions located on the square voids of the two-dimensional Ce-pdc bilayer. Compounds 2a-c are isostructural and constructed from 3D Ln-pdc-based metal-organic framework (MOF) incorporating noncoordinating guests Keggin structure [SiW₁₂O₄₀]⁴⁻. Solid-state properties of compounds 1 and 2a-c such as thermal stability and photoluminescence have been further investigated.     

Hydrothermal Synthesis and Crystal Structure of One Rare Earth Substituted Keggin-Type Germanotungstate [Cu(en)2]2[Cu(en)2(H2O)]2H3{[Cu(en)2]2[Na2(H2O)1.75][K(H2O)3][Dy2(H2O)2 (GeW11O39)3]} · 6H2O

A novel germanotungstate derivative based on the dysprosium cation and monovacant Keggin anion, [Cu(en)₂]₂[Cu(en)₂(H₂O)]₂H₃{[Cu(en)₂]₂[Na₂(H₂O)_1.75][K(H₂O)₃][Dy₂(H₂O)₂(GeW₁₁O₃₉)₃]} · 6H₂O(en = ethylenediamine) 1, has been synthesized by hydrothermal method and characterized by elemental analysis, IR-UV spectroscopy, thermal analysis and single-crystal X-ray diffraction. In the compound, one kind of clusters with the Dy³⁺/[GeW₁₁O₃₉]^8? ratio of 2:3 was observed. Especially, the 2:3 type displays the novel cluster based on the rare earth and monolacunary Keggin polyoxometalate.     

Coordinate Structures of PrIII, GdIII, TmIII, and YbIII Complexes with Nitrilotriacetic Acids

The crystal and molecular structures of the [Pr^III(nta)(H₂O)₂]·H₂O (nta = nitrilotriacetic acids), K₃[Gd^III(nta)₂(H₂O)]·6H₂O, and K₃[Yb^III(nta)₂]·5H₂O complexes have been determined by single-crystal X-ray structure analyses. In [Pr^III(nta)(H₂O)₂]·H₂O, the Pr^IIINO₈ part forms a nine-coordinate pseudo-monocapped square antiprismatic structure in which one N and three O atoms are from one nta ligand in the same molecule, three O atoms from another nta ligand in the neighboring molecule and two O atoms from two coordinate water molecules. In K₃[Gd^III(nta)₂(H₂O)]·6H₂O, the [Gd^III(nta)₂(H₂O)^3- complex anion has a nine-coordinate pseudo-monocapped square antiprismatic structure in which each nta acts as a tetradentate ligand with one N atom of the amino group and three O atoms of the carboxylic groups. In K₃[Yb^III(nta)₂]·5H₂O, each nta also acts as a tetradentate ligand with one N atom of amino group and three O atoms of the carboxylic groups, but the [Yb^III(nta)₂ ^3- complex anion has an eight-coordinate structure with a distorted square antiprismatic prism. All the results including those for [Tm^III(nta)(H₂O)₂]·2H₂O confirm the inferences on the coordinate structures and coordination numbers of rare earth metal complexes with the nta ligand.     

Diverse Ligand‐Functionalized Mixed‐Valent Hexamanganese Sandwiched Silicotungstates with Single‐Molecule Magnet Behavior

Under hydrothermal conditions, replacement of the water molecules in the [Mn^III₄Mn^II₂O₄(H₂O)₄]⁸⁺ cluster of mixed‐valent Mn₆ sandwiched silicotungstate [(B‐α‐SiW₉O₃₄)₂Mn^III₄Mn^II₂O₄(H₂O)₄]^12? ( 1 a ) with organic N ligands led to the isolation of five organic–inorganic hybrid, Mn₆‐substituted polyoxometalates (POMs) 2 – 6 . They were all structurally characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, diffuse‐reflectance spectroscopy, and powder and single‐crystal X‐ray diffraction. Compounds 2 – 6 represent the first series of mixed‐valent {Mn^III₄Mn^II₂O₄(H₂O)_4?n(L)_n} sandwiched POMs covalently functionalized by organic ligands. The preparation of 1 – 6 not only indicates that the double‐cubane {Mn^III₄Mn^II₂O₄(H₂O)_4?n(L)_n} clusters are very stable fragments in both conventional aqueous solution and hydrothermal systems and that organic functionalization of the [Mn^III₄Mn^II₂O₄(H₂O)₄]⁸⁺ cluster by substitution reactions is feasible, but also demonstrates that hydrothermal environments can promote and facilitate the occurrence of this substitution reaction. This work confirms that hydrothermal synthesis is effective for making novel mixed‐valent POMs substituted with transition‐metal (TM) clusters by combining lacunary Keggin precursors with TM cations and tunable organic ligands. Furthermore, magnetic measurements reveal that 3 and 6 exhibit single‐molecule magnet behavior.     

A new organic-inorganic hybrid material constructed from Keggin polyanion and transition metal complexes: [Co(2,2′-bipy)3]1.5[SiWVWVI 11O40Co(2,2′-bipy)2(H2O)] · 0.5H2O

A new organic-inorganic hybrid compound constructed from Keggin-type polyanion clusters and transition metal complexes, [Co(2,2′-bipy)₃]_1.5[SiW^VW^VI ₁₁O₄₀Co(2,2′-bipy)₂(H₂O)] ·?0.5H₂O (1), has been hydrothermally prepared and characterized by elemental analysis, IR, UV–Vis, TG-DTA and single crystal X-ray diffraction. Compound 1 crystallized in the monoclinic system, space group C2/c, a =?46.995(15), b =?14.487(5), c =?26.205(9)Å, β =?90.000(0)°, V =?17841(10)ų, Z =?4. Compound 1 contains a [SiW^VW^VI ₁₁O₄₀Co(2,2′-bipy)₂(H₂O)]^3? polyoxoanion in which [Co(2,2′-bipy)₂(H₂O)]²⁺ is covalently bonded to the α-Keggin-type heteropolyanion [SiW^VW^VI ₁₁O₄₀]^5? via a terminal oxygen.