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One halide ion (X- ) can bind on the surface of nanoscale Anderson-type polyoxometalate (POMs) clusters [(n-C4 H9 )4 N]3 {AlMo6 O18 (OH)3 [(OCH2 )3 CCH3 ]}, and form stable complexes in solution with binding constant K=1.53×103 . Single-crystal structural analysis showed that this binding behavior occurs through multiple hydrogen bonding between X- and three hydroxy groups on the uncapped side of the cluster. This supramolecular interaction in the cluster systems means that their catalytic activities, evaluated from the oxidation of alcohols to aldehydes, can be switched upon the introduction of halide ions and water molecules. The halide ions work as inhibitors by blocking the active sites of the clusters while they can be re-activated by the addition of water.

Engineering photoredox-triggered chemical transformation via visible light has been an emerging area in organic synthesis. However, most of the well-established photocatalysts are based upon either transition metal complexes involved with noble metals and organic ligands or photosensitive organic dyes, the development of pure inorganic molecular photocatalysts that could provide better stability and durability is greatly retarded. Herein we discover that the Anderson polyoxometalate (POM) Na-4[NiMo6O18(OH)(6)] (1), which consists of pure inorganic framework built from a central Ni-II core supported by six (MoO6)-O-VI inorganic scaffold/ligands, can be used as a powerful photocatalyst. Upon irradiation with visible light (>400 nm), the compound can catalyze, in high efficiency, a wide range of reactions, including the oxidative cross-coupling reaction of chlorides with amines, as well as oxidation of chlorides using molecular oxygen, affording various imines, aldehydes, and ketones, respectively in high selectivity and good yields. Owing to the robust inorganic framework, this catalyst exhibits excellent stability during the catalysis and reusability with little loss of the catalytic activity, thus providing an alternative without use of complicated organic ligands and expensive noble metal-based photosensitizers.

A series of rod-shaped polyoxometalates (POMs) [Bu4 N]7 [Mo6 O18 NC(CH2 O)3 MnMo6 O18 (OCH2 )3 CNMo6 O18 ] and [Bu4 N]7 [ArNMo6 O17 NC(CH2 O)3 MnMo6 O18 (OCH2 )3 CNMo6 O17 NAr] (Ar=2,6-dimethylphenyl, naphthyl and 1-methylnaphthyl) were chosen to study the effects of cation-π interaction on macroionic self-assembly. Diffusion ordered spectroscopy (DOSY) and isothermal titration calorimetry (ITC) techniques show that the binding affinity between the POMs and Zn2+ ions is enhanced significantly after grafting aromatic groups onto the clusters, leading to the effective replacement of tetrabutylammonium counterions (TBAs) upon the addition of ZnCl2 . The incorporation of aromatic groups results in the significant contribution of cation-π interaction to the self-assembly, as confirmed by the opposite trend of assembly size vs. ionic strength when compared with those without aromatic groups. The small difference between two aromatic groups toward the Zn2+ ions is amplified after combining with the clusters, which consequently triggers the self-recognition behavior between two highly similar macroanions.

An unprecedented class of benzoyldiazenido functionalized polyoxometalates, (Bu4N)3[Mo6O18(=N=NCOAr)] (Ar = Ph, 1; Ph-o-Cl, 2; Ph-m-Cl, 3; Ph-p-Cl, 4; Ph-o, p-Cl2, 5; Ph-p-Br, 6; Ph-m-NO2, 7; Ph-p-NO2, 8; Ph-p-OMe, 9) are prepared via the refluxing reaction of α-octamolybdates and corresponding hydrazides in dry acetonitrile using dicyclohexylcarbodiimide (DCC) as dehydrating agent. Single crystal X-ray diffraction structural analysis reveals that their anions demonstrate typical structural features of mono-functionalized hexamolybdates with different organic substituents. 1H NMR indicates that the [Mo6O18(NN)] fragment in these compounds is an electron-donating group rather than an electron-withdrawing group, which is further validated by the calculation of atomic charge distribution(natural bond orbital (NBO) and Mulliken). Bond valence sum (BVS) shows that the oxidation state of all molybdenum atoms is +6. Cyclic voltammetry (CV) indicates that they are more difficult to be reduced than hexamolybdate and its organoimido derivatives. Anti-tumour activity test against K562 shows that most hybrid compounds have an enhanced inhibitory activity compared to hexamolybdate and corresponding hydrazide ligands.

A redox-responsive hybrid of polyoxometalate and conducting oligomer including its self-assemblies with controllable morphologies are reported. To this end, a hybrid molecule, containing a Lindqvist hexamolybdate as the polar head group and N,N'-bis(4'-amino-2,6-dimethylphenyl)-1,4-quinonediimine as the redox-responsive and aggregating group, is prepared. This hybrid exhibits redox-responsive behavior with controllable assembling morphological transition from spherical vesicles to short cylindrical vesicles. Besides, the hybrid-based self-assemblies are transferred to the surface, thus the surface wettability can be well-tuned owing to the morphological transitions of the self-assemblies. By marrying conducting materials with polyoxometalate chemistry, this research opens a new horizon of polyoxometalate-based self-assembled systems with potential applications in functional materials.

The first example of a heterogeneous iron(III)-catalyzed aerobic oxidation of aldehydes in water was developed. This method utilizes 1 atmosphere of oxygen as the sole oxidant, proceeds under extremely mild aqueous conditions, and covers a wide range of various functionalized aldehydes. Chromatography is generally not necessary for product purification. Its operational simplicity, gram-scale oxidation, and the ability to successively reuse the catalyst, make this new methodology environmentally benign and cost effective. The generality of this methodology gives it the potential to be used on an industrial scale.

Herein we report a step-by-step strategy for the organic modification of polyoxovanadates, which is based on a suitable polyoxovanadate platform, and a series of novel functionalized polyoxovanadates can be synthesized conveniently by sequential esterification and amidation reactions.

Trifluoromethylation of tetraphenlyborate counterions was successfully used to improve the electrochemical stabilities and device performance of cationic iridium(III) complexes. Melioration of the thermal, photoluminescent, electrochemical, and electrophosphorescent characteristics was achieved. Interionic hydrogen bonds were first found between the aromatic hydrogen atoms in the ancillary ligands of cations and the fluorine atoms in the trifluoromethyl groups of the anions. The strong impact of the counterions on the charge transport in the devices was investigated. A compound with two trifluoromethyl groups in the tetraphenlyborate ion shows the highest photoluminescent efficiency, the best electrochemical stability, and the greatest performance in green-blue-emitting devices, with a high current efficiency of 12.4 cd A(-1) and an emission peak at λ=480 nm. The efficiencies achieved are the highest reported for OLEDs with ionic complexes emitting in the blue-green region.

On the basis of the well-developed N,N′-dicyclohexylcarbodiimide (DCC) imidoylization strategy, the novel trans-dinitrosyl-substituted polyoxometalate (POM) (NBu4)4[Mo6O17(≡NO)2] was synthesized in moderate yield with high purity through a highly selective reaction route under mild reaction conditions. Its structure was elucidated by IR and UV/Vis spectroscopy, ESI-MS, and single-crystal X-ray diffraction studies. Furthermore, its ability to undergo controlled NO release was confirmed by ESI-MS, and a curve of the amount of NO released as a function of time within a simulated body fluid system was obtained by UV spectroscopy. The rate of NO release is controlled by changing the pH of the system. This is the first time that the decomposition of a POM has been used to produce therapeutic NO species. This study provides a new route to controlled-release technology for NO storage and targeted delivery.

A series of nanorod-like organic-inorganic hybrids based on hexamolybdate and Anderson-type heteropolyoxomolybdates has been prepared using the well-developed DCC protocol. The present work opens a way to flexibly introduce two different functional groups to a hexamolybdate ion and explore thoroughly the whole family of organoimido derivatives for fabricating novel molecular nanostructures with tunable properties.

The functionalization of polyoxometalates (POMs), especially with an amino group to yield organonitrogenous derivatives of POMs, is an efficient approach to the enrichment of their structures and the diversification of their properties for various applications. The mechanism for the formation of organonitrogenous-derivatized hexamolybdates was explored by investigating the monofunctionalization of the [Mo(6)O(19)](2-) ion with methylamine using the density functional theory (DFT) method. The calculations show that the direct imidoylization of hexamolybdate with methylamine is both kinetically and thermodynamically unfavorable. However, this imidoylization was found to take place readily in the presence of dimethylcarbodiimide (DMC), for which the free-energy barrier was calculated to be +32.5 kcal mol(-1) in acetonitrile. Moreover, various factors controlling the efficiency of the imidoylization were examined. The calculations show that [W(5)MoO(19)](2-) has a relatively lower reactivity than [Mo(6)O(19)](2-), and that the imidoylization of [W(6)O(19)](2-) is an unfavorable process. With respect to the effect of carbodiimides, it is found that the catalytic activity is directly proportional to the electron-withdrawing effects of the substituents. As to the reactivity of R-NH(2) , the computation results indicate that the free-energy barriers of the substitution reactions are linearly correlated with the basicity constants (pK(b)) of the amino groups. It is noteworthy that the introduction of the proton dramatically decreases the free-energy barrier of the imidoylization of [Mo(6)O(19)](2-) catalyzed by DMC to 24.3 kcal mol(-1) in acetonitrile.

Polyoxometalate (POM)-based organic–inorganic hybrid materials have attracted extensive attention in the last ten years due to their potential applications in catalysis, nonlinear optics, photovoltaic, and self-assembly research. Currently, trisalkoxo tripodal ligand (Tris)-functionalized Lindqvist-, Anderson-, and Dawson-type POMs show high stability and varied functionalities. Zubieta et al. used Tris ligands to stabilize macro-POM clusters and to functionalize hexavanadate. The functionalized hexavanadate was further developed by Hill and co-workers for the construction of metal–organic frameworks, which can function as highly efficient heterogeneous catalytic materials. Due to the high reactivity of vanadate, vanadium-containing Dawsontype POMs were observed to be capped by only one Tris ligand. In particular, after Hasenknopf et al. had established the synthesis of Tris derivatives of Anderson-type POMs in 2002, the groups of Cronin and Hasenknopf introduced different kinds of functional groups to the system through further organic reactions. The resulting materials show interesting functions including high biological activity against cells, photocatalytic properties, and interesting selfassembly behavior. Due to their high symmetry (D3d), both sides of Anderson-type POMs are easily functionalized simultaneously by Tris ligands during their synthesis, which seems to be an unquestionable fact (Figure 1), and there has never been any report on a single-sided functionalized Anderson-type POM with Tris. Herein, we report the synthesis and characterization of Anderson-type POMs with only one side functionalized by a Tris ligand, which not only afforded asymmetric POM-based hybrid materials for further research, but also uncovered more structural and reactive properties of Anderson-type POMs, and the reaction mechanism for the functionalization of POMs with Tris. In the previous protocol, to synthesize the double-sided functionalized Anderson-type POMs, octamolybdate, a salt of the central heteroatom, and organic ligands (Tris) were mixed in an organic solvent, such as acetonitrile, and the final products were obtained after heating to reflux for approximately 16 hours, which is a classical one-pot reaction. However, our new protocol to synthesize the single-side organically functionalized Anderson-type POM, [(C4H9)4N]5{H7ACHTUNGTRENNUNG[HOCH2C ACHTUNGTRENNUNG(CH2)3 ACHTUNGTRENNUNG(CrO6)Mo6O18]2} (1), is a two-step aqueous reaction with high yield through the direct functionalization of the parent Anderson-type POM, [CrMo6O18(OH)6] 3 . Compound [CrMo6O18(OH)6] 3 was first synthesized according to Perloff s method reported in 1970. Pentaerythritol was then added to the resulting aqueous solution of [CrMo6O18(OH)6] 3 , and the mixture was refluxed at once for a prolonged time to finish the esterification. Interestingly, the reaction is of high yield and high selectivity for the mono Tris-functionalized product 1, probably due to the hierarchical synthesis protocol and aqueous reaction media (see the Experimental Section). In the preparation reaction, a single-side-functionalized Anderson-type POM is obtained in high yield (based on Mo), even when the ratio of Tris to the parent Anderson-type POM is two or much higher than two. Therefore, the selectivity for producing such single-sided species might be related to the aqueous environment. [a] P. Wu, P. Yin, Dr. J. Zhang, Dr. J. Hao, Dr. Z. Xiao, Prof. Dr. Y. Wei Department of Chemistry, Tsinghua University Beijing, 100084 (P.R. China) Fax: (+86)10-6277-1149 E-mail : yinpanchao@tsinghua.org.cn yonggewei@tsinghua.edu.cn [b] P. Wu Institute of POM-based Materials Key Laboratory of Fermentation Engineering (Ministry of Education) Hubei University of Technology Wuhan, 430068 (P.R. China) [c] Prof. Dr. Y. Wei Key Laboratory of Cluster Science (Beijing Institute of Technology) Ministry of Education of China Beijing, 100081 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101552. Figure 1. Molecular structures of: a) unfunctionalized and b) bifunctionalized Anderson-type POMs. Color code: Mo: large black sphere; Cr: central gray sphere; O: small black sphere; C: large gray sphere; H: small gray sphere; X= functional group: -CH2OH, -NH2, -CH3, or -NO2.

The first mixed-valent octamolybdate anion [Mo(V)(4)Mo(VI)(4)O(24)](4-), termed χ-octamolybdate due to its shape, was obtained by partial reduction of α-(Bu(4)N)(4)-[Mo(8)O(26)] in dry acetonitrile. Single-crystal X-ray structure analysis revealed that the anion includes an unusual Mo(V)(4)O(8) cubane-like cluster core, whose four side faces are capped by four MoO(4) units to form a crosslike cluster. X-ray photoelectron spectroscopy (XPS) and bond valence sum (BVS) calculations were carried out to validate the presence of mixed-valent Mo centers.

Ultrafine SnO2 nanocrystals are synthesized through a surfactant-assisted solvothermal route in water–ethanol mixed media. SnO2 photocatalysts with sizes of about 4, 8, and 12 nm are prepared through controllable annealing of the as-synthesized nanocrystals. Brunauer–Emmett–Teller (BET) specific surface areas of calcined SnO2 samples increase dramatically as their sizes decrease. Photocatalytic performances of the as-obtained catalysts for decomposing ppb-level (parts per billion) acetaldehyde are tested in a continuous glass-plate reactor. Result shows that SnO2 photocatalysts of about 4 nm with a large BET surface area of 130 m2 g−1 exhibit the best photocatalytic oxidation properties, which is comparable to that of Degussa P25 TiO2. Analysis by using the unimolecular Langmuir–Hinshelwood reaction model indicates that the abilities of adsorption have well synergized with the photocatalytic reaction activities in the as-obtained SnO2 samples. This synergism finally enhances the photocatalytic performance of the as-prepared SnO2 photocatalysts.

A novel coordination polymer, [Ag4ppdc)(H2bpdc)(Hbpdc)2] (bpdc = 2,2′-bipyridyl-3,3′-dicarboxylate), was hydrothermally synthesized at 403 K and structurally characterized by single crystal X-ray diffraction analysis. The compound crystalizes in the monoclinic space group C2/c with a=1.9516(4) nm, b=1.9503(4) nm. c=1.2566(3) nm, and β=112.48(3)°. In the two-dimensional crystal structure, AgI center is coordinated, in a scarce coordination environment, double-capped tetrahedron, by one bpdc ligand to form N-Ag-N chelate bond via two pyridyl N atoms, and other two bpdc ligands to form two O-Ag-O chelate bonds, respectively, via two carboxyl O atoms. The bpdc ligands are present in one non-protonated form, bpdc, and two protonated forms, Hbpdc and H2bpdc, which all act as μ3-ligand in a hexadentate fashion (N, N′; O, O′; O, O′) to coordinate with three Ag centers, respectively, through the three chelate bonds. This coordinated fashion of bpdc ligand is first found in the title compound. W-Us-NIR reflectance spectroscopy study revealed insulator nature for the crystal with an optical energy gap of 3.1 eV.

Two new hybrids of local anesthetic analogs and polyoxometalates {(Bu4N)2[Mo6O18NC6H4COOCH3] (1) and (Bu4N)2[Mo6O18NC6H4COOC2H5] (2)} have been prepared in high purity and moderate yields using the easy reaction route of [α-Mo8O26]4– with corresponding aromatic amine hydrochlorides in the presence of a N,N′-dicyclohexylcarbodiimide (DCC), and have been characterized by 1H NMR, IR, UV/Vis, ESI-MS, and single-crystal X-ray diffraction study. Compound 1 crystallizes in the triclinic space group P with dimer structure, while Compound 2 crystallizes in the monoclinic space group P21/n with dimer and chain structure. These two hybrids have the typical Mo≡N triple bond that links a phenylimido group in local anesthetic analogs to the Mo atom of a hexamolybdate cluster. Because the formed Mo≡N bond is not stable in basic solution, this property is useful and could be developed as a novel controlled-release technology for drug delivery.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Organically derivatised polyoxometalate (POM) clusters containing bromo or iodo groups can undergo ligand-free, Pd-catalysed Heck carbon-carbon coupling reactions with alkenes, with bromomagnesium phenylamide as a base (see scheme). This protocol offers a new route to organic-inorganic hybrid molecular materials in which POM clusters are covalently bonded with organic conjugated segments.

We report the synthesis and excellent two-photon-sensitized luminescence properties of a new complex [Eu(tta) 3 dmbpt] (tta = henoyltrifluoroacetonate; dmbpt=2-(N,N-diethyl-2,6-dimethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) that exhibits the highest efficiency of lanthanide luminescence when excited by near-infrared (NIR) laser pulses (action cross section of two-photon-excited fluorescence δ x Φ F : 85 GM at 812 nm and 56 GM at 842 nm; 1 GM =10 -50 cm 4 s photon -1 molecule ). Compared to a previously reported [Eu(tta) 3 dpbt] complex, (dpbt = 2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine), [Eu(tta) 3 dmbpt] has two excess methyl groups at the 2,6-positions of the phenyl ring. Crystallographic data of dmbpt show that the 2,6-dimethyl substitutes bring about a significant twist in the conformation of the diethylamino group compared to that in dpbt, which severely influences the conjugation in the ground state between the electron lone pair of N in the -N(CH 2 -) 2 moiety and the aromatic electron system in dmbpt. The large two-photon absorption (TPA) cross section of dmbpt is mainly derived from its large static dipole moment difference between the So and the S 1 states, which is partly responsible for the high capability of two-photon-sensitized luminescence of [Eu(tta) 3 dmbpt]. The broader two- and single-photon excitation windows and the superior two-photon-sensitized luminescent properties in the long-wavelength NIR region of [Eu(tta) 3 dmbpt] compared to [Eu(tta) 3 dpbt] are also explained according to the calculated results and twisted structure.

The crystal structure of hexaammonium diacetyl-octa-molybdate tetrahydrate, (NH4)42[Mo132O372 (CH3COO)30(H2O)72] is documented. The crystals are triclinic, space group P-1, with a=8.1018(16) A, b=10.334(2) A, c=12.238(2) A, α=68.20(3)°, β=74.98(3)°, γ=67.25(3)°, V=869.3(3) A3, Z=1. The structure was solved by direct methods and refined by least squares methods to a Final R1 = 0.0374 and wR2 = 0.1074 for 3805 observed reflections with I > 2σ(I). The structure contains ammonium cations and isolated acetyl octamolybdate(6-) anions, [Mo8O28(CH3CO)2]6-. The crystallographic data of the structure was deposited with the Cambridge Data Center as No. CCDC 249565. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In the presence of N, N′-dicyclohexylcarbodiimide (DCC), (Bu4N)2[Mo6O18(NAr)] (1) and (Bu4N)2[Mo6O17(NAr)2] (2), Ar = o-CH3C6H4, have been synthesized via the reaction of [α-Mo8O26]4— with o-toluidine. If the hydrochloride salt of o-toluidine was added into the reactive mixture, only the monofunctionalized imido derivative of [Mo6O19]2— was obtained; the bifunctionalized derivative of [Mo6O19]2— was exclusively synthesized in the presence of non-protonated o-toluidine. The molecular and crystal structures of the hybrid compounds 1 and 2 were determined by X-ray single crystal diffraction, and their UV, IR and NMR spectra were compared. Additionally, a possible reaction mechanism was proposed.

In the presence of a carbodiimide (DCC) a proton can dramatically speed up the reaction of α-[Mo8O26]4− with aromatic amines under mild conditions and convenient bench manipulations, which results in the easy synthesis of monofunctionalized organoimido derivatives of [Mo6O19]2− even bearing an electron-withdrawing group such as bromo or chloro groups. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The efficient evolution of hydrogen through electrocatalysis is considered a promising approach to the production of clean hydrogen fuel. Platinum (Pt)-based materials are regarded as the most active hydrogen evolution reaction (HER) catalysts. However, the low abundance and high cost of Pt hinders the large-scale application of these catalysts. Active, inexpensive, and earth-abundant electrocatalysts to replace Pt-based materials would be highly beneficial to the production of cost-effective hydrogen energy. Herein, a novel organoimido-derivatized heteropolyoxometalate, Mo4-CNP, is designed as a precursor for electrocatalysts of the HER. It is demonstrated that the carbon, nitrogen, and phosphorus sources derived from the Mo4-CNP molecules lead to in situ confined carburization, phosphorization, and chemical doping on an atomic scale, thus forming nitrogen-doped porous molybdenum carbide and phosphide hybrids, which exhibit remarkable electrocatalytic activity for the HER. Such an organically functionalized polyoxometalate-assisted strategy described here provides a new perspective for the development of highly active non-noble metal electrocatalysts for hydrogen evolution.

The chemistry of organoimido derivatives of polyoxometalates (POMs) has received increasing interest. In recent decades, a great development of the synthetic chemistry of organoimido derivatives of POMs using different imido-releasing reagents has taken place, particularly the novel DCC-dehydrating protocol to prepare organoimido derivatives of POMs was developed recently by us and co-workers. Organoimido substituted POMs as valuable building blocks can construct novel nanostructured organic-inorganic hybrid molecular materials in well-developed common organic synthesis methods, such as Pd-catalyzed carbon-carbon coupling and esterification. Therefore, the reactive chemistry of organoimido derivatives of POMs stands for the fascinating future of the chemistry of organoimido derivatives of POMs.

The reduced octamolybdate (II) crystallizes in the triclinic space group P with Z = 2 (single crystal XRD).

The Mo≡N bond is conjugated with the organic segment in the novel molecular organic-inorganic hybrid materials that have been obtained by Pd-catalyzed coupling of an iodo-functionalized hexamolybdate anion and an alkyne (see scheme; Ar=4-methylphenyl,3-5-di(tert-butyl)phenyl). The interaction between the polyoxometalate cluster and the organic conjugated system is particularly apparent from the strong red-shifted absorption in the UV/Vis spectrum.

Reduction of an acidified solution of Na2MoO4·2H2O by iron powder results in the formation of the title compound [Mo176O16O480(OH)32(H2O)80]; the compound is tyre shaped and consists of sixteen {Mo8} subunits being linked by forty-eight MoO6 octahedra; remarkable features are the size and mass (which is of the order of a protein) and its nanodimensional cavity of ca. 3 nm in diameter.