Efficient Preparation of Functionalized Hybrid Organic/Inorganic Wells−Dawson-type Polyoxotungstates

A New Method for the Synthesis of Organopolyoxometalate Hybrid Compounds

The reaction of a quaternary ammonium salt of the tin chloride-substituted polyoxometalate, [PSn(Cl)W11O39]4-, with a variety of n-nucleophiles including primary, secondary, and tertiary amines and a tertiary phosphine, yielded tin-centered Lewis acid-base adducts, [PSn(Cl)W11O39]4--n-nucleophile; with more nucleophilic secondary amines such as diisopropylamine, apparently some [PSnN[CH(CH3)2]2W11O39]4- was formed as a minor product. The compounds were identified by 1H, 119Sn, 15N, 31P, and 183W NMR, ESI-MS, and elemental analyses. The key connectivity of the Sn-Cl center with the amine was clarified by the observation of 3J Sn-H couplings (Sn from the polyoxometalate cluster and H from the amine moiety) in a 2D 119Sn-1H heteronuclear multiple-bond correlation NMR experiment. This new, rather simple synthetic method was also utilized for preparing amino acid-polyoxometalate hybrid compounds.

Organic−Inorganic Hybrids Constructed of Anderson-Type Polyoxoanions and Oxalato-Bridged Dinuclear Copper Complexes

Two novel organic-inorganic hybrid compounds based on Anderson-type polyoxoanions, [Cu2(bpy)2(mu-ox)][Al(OH)7Mo6O17] (1) and [Cu2(bpy)2(mu-ox)][Cr(OH)7Mo6O17] (2), have been synthesized and characterized by elemental analyses, IR, and X-ray powder diffraction. The crystal structures of 1 and 2 have been established by single-crystal X-ray diffraction, which reveals the presence of 1D chains constructed of alternating Anderson-type polyoxoanions and oxalato-bridged dinuclear copper complexes for both compounds and extensive hydrogen bonding that plays an important role in the formation of the 3D supramolecular network structures of 1 and 2. To elucidate the electronic properties and magnetic properties of the metal ions (Cu2+ or Cu2+ and Cr3+), EPR studies and magnetic susceptibility studies have been performed, respectively. The results are consistent with the structural feature of these compounds.

A Novel Hexatungstate Fragment Stabilized by Dimethyltin Groups: [{(CH3)2Sn}2(W6O22)]4-

Reaction of Na2WO4 and (CH3)2SnCl2 in water (pH 7) led to the formation of the hybrid organic-inorganic polyanion [{(CH3)2Sn}2(W6O22)]4- (1), which is composed of a novel hexatungstate core stabilized by two dimethyltin groups. Selective crystallization of 1 with guanidinium cations resulted in [C(NH2)3]4[{CH3)2Sn}2(W6O22)]2H2O (1a), which exhibits a 1D arrangement via distorted trigonal-bipyramidal cis-(CH3)2SnO3 moieties.

Hybrid Organic−Inorganic Assemblies Based on Molybdates and Dimethyltin Linkers

Reaction of (CH3)2SnCl2 with Na2MoO4 in an aqueous medium results in three different compounds depending on the pH: [{(CH3)2Sn}(MoO4)] (1), [{(CH3)2Sn}4O2(MoO4)2] (2), and [{(CH3)2Sn}{Mo2O7(H2O)2}].H2O (3). All three species have been characterized in the solid state by means of elemental analysis, infrared spectroscopy, thermogravimetry, and single-crystal X-ray diffraction. Compounds 1-3 all show hybrid organic-inorganic extended lattices based on molybdate anions linked by (CH3)2Sn2+ moieties, and the coordination numbers of the Sn(IV) centers range from 5 to 7. Compound 1 crystallizes in the orthorhombic space group Pnma with cell parameters a = 13.2035(4) A, b = 7.2634(2) A, c = 7.1458(2) A, and Z = 4. 1 exhibits a complex, 3-dimensional network structure constructed of corner-shared, tetrahedral orthomolybdate oxoanions and distorted octahedral trans-(CH3)2SnO4 groups. Compound 2 crystallizes in the monoclinic space group P2(1)/n with cell parameters a = 8.2330(1) A, b = 11.4033(2) A, c = 12.1529(2) A, beta = 91.566(1) degrees , and Z = 2. Its 2-dimensional layered structure contains dimeric tetramethyldistannoxane [{(CH3)2Sn}4O2]2+ subunits built up of edge-sharing cis-(CH3)2SnO4 distorted trigonal bipyramids and connected in the (1,0,) plane by tetrahedral orthomolybdate oxoanions, the layers packing along the crystallographic a axis with the methyl groups pointing to the interlamellar space. Compound 3 crystallizes in the orthorhombic space group Pbcm with cell parameters a = 6.5594(4) A, b = 14.2465(11) A, c = 11.3892(8) A, and Z = 4. It shows dimeric [Mo2O8(H2O)2] units sharing corners to form zigzagging polymeric {[Mo2O7(H2O)2]2-}infinity polyanions along the [001] direction; these chains are further linked by trans-(CH3)2SnO5 distorted pentagonal bipyramids to give layers parallel to the (010) plane, the interlamellar space being occupied by hydrogen-bonded hydration water molecules.

Production and Reactions of Organic-Soluble Lanthanide Complexes of the Monolacunary Dawson [α1-P2W17O61]10- Polyoxotungstate

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.

Novel charge transfer supramolecular assemblies with Keggin anions and 2-amino-5-nitropyridine

Several novel compounds with the non-linear optical chromophore 2-amino-5-nitropyridine (2A5NP) and Keggin polyoxoanions (alpha-isomers), having the general formula (2A5NP)(m)H(n)[XM12O40].xH2O, M = Mo, W, were synthesised. Compounds were obtained with X = P, n = 3, m = 3 and 4 and X = Si, n = m = 4 (x = 2-6). Thus, for each of the anions [PMo12O40]3- and [PW12O40]3- two different compounds were obtained, with the same anion and organic counterpart but with a different stoichiometric ratio. These presented different charge transfer properties and thermal stability. All compounds were characterised by spectroscopic and analytical techniques. The single crystal X-ray diffraction structure of (2A5NP)4H3[PMo12O40].2.5H2O.0.5C2H5OH showed that the water solvent molecules and the organic chromophores are assembled via infinite one-dimensional chains of hydrogen bonds with formation of open channels, which accommodate [PMo12O40]3- and ethanol solvent molecules.

Tetrakis(dimethyltin)-Containing Tungstophosphate [{Sn(CH3)2}4(H2P4W24O92)2]28-: First Evidence for a Lacunary Preyssler Ion

We demonstrate for the first time that the superlacunary polyanion [H(2)P(4)W(24)O(94)](22)(-) reacts with electrophiles. One-pot reaction of this precursor polyanion with dimethyltin dichloride in aqueous acidic medium results in the hybrid organic-inorganic [{Sn(CH(3))(2)}(4)(H(2)P(4)W(24)O(92))(2)](28)(-) (1). Single-crystal X-ray analysis was carried out on K(17)Li(11)[{Sn(CH(3))(2)}(4)(H(2)P(4)W(24)O(92))(2)].51H(2)O (1a), which crystallizes in the tetragonal system, space group P4(2)/nmc, a = b = 21.5112(17) and c = 27.171(3) A, and Z = 2. Polyanion 1 is composed of two (P(4)W(24)O(92)) fragments that are linked by four equivalent diorganotin groups. The unprecedented assembly 1 has D(2)(d)() symmetry and contains a hydrophobic pocket in the center of the molecule. The cyclic voltammetry pattern of 1 is constituted by a first broad, 16-electron reduction wave followed by a second large current intensity wave. No splitting of the first reduction wave could be obtained at moderate scan rate values, even though two well-separated oxidation processes are associated with it. The characteristics of the first wave are clearly different from those obtained for the polyanion precursor [H(2)P(4)W(24)O(94)](22)(-) and the related, wheel-shaped [H(7)P(8)W(48)O(184)](33)(-), which is due to the {Sn(CH(3))(2)} fragments in 1. However, no feature was observed in the voltammogram which could be associated with reduction of the Sn centers.

Enantiopure 1,1‘-Binaphthyl-Based Polyoxometalate-Containing Molecular Hybrids

The first chiral molecular hybrids based on covalently linked polyoxometalate clusters and enantiopure 1,1'-binaphthyl units have been prepared. Their structures have been confirmed by (1)H NMR, FTIR, and ESI-MS measurements. Such hybrids show moderate chiroptical behavior in solutions, and Cotton effects are observed up to 450 nm, indicating chiral extension from the binaphthyl core to the cluster-containing pi-conjugated arms.