New Routes for Multiple Derivatization of Polyoxometalates. Bis(acetato)dirhodium-11-tungstophosphate, [(PO4)W11O35{Rh2(OAc)2}]5-

Highly Active and Dispersed Pd Nanoparticles Stabilized by Lacunary Phosphomolybdate: Synthesis, Characterization, and Liquid Phase Hydrogenation of Levulinic Acid to γ-Valerolactone

In the current scenario, one of the crucial reaction conversions is the synthesis of renewable biofuels and value-added chemicals from the hydrogenation of biomass. Therefore, in the present work, we are proposing aqueous phase conversion of levulinic acid to γ-valerolactone via hydrogenation using formic acid as a sustainable green hydrogen source over a sustainable heterogeneous catalyst. The catalyst based on Pd nanoparticles stabilized by lacunary phosphomolybdate (PMo₁₁Pd) was designed for the same and characterized by EDX, FT-IR, ³¹P NMR, powder XRD, XPS, TEM, HRTEM, and HAADF-STEM analyses. A detailed optimization study was done to achieve maximum conversion (95% conversion), using a very small amount of Pd (1.879 × 10^-3 mmol) with notable TON (2585) at 200 °C in 6 h. The regenerated catalyst was found to be workable (reusable) up to three cycles without any change in activity. Also, a plausible reaction mechanism was proposed. The catalyst exhibits superior activity against reported catalysts.

Synthesis, Structure, and Catalytic Activities of Two Multi-Rh-Decorated Polyoxometalates

Two multi-Rh-incorporated polyoxometalates [NH₂(CH₃)₂]₁₀[Na₄(H₂O)₈]H₃[As₄W₄₂O₁₄₂(OH)₄(CH₃COO)₂Rh₃(H₂O)₄]·13H₂O·4[NH(CH₃)₂] (1) and [K₄Na(H₂O)₆]KH₁₀[As₄W₄₀O₁₄₀Rh₄(H₂O)₄]·34H₂O (2) have been synthesized in acetate buffer solution. Polyanion 1a is built up atop of an acetate-modified rectangular framework [As₄W₄₂O₁₄₂(OH)₄(CH₃COO)₂]^26-, while polyanion 2a contains a pure inorganic cryptand [As₄W₄₀O₁₄₀]^28-. All Rh atoms of these two compounds share the same hexa-coordinate distorted-octahedral geometry and are embedded into their cavities through As-Rh bonding with a bond length around 2.304(4)-2.436(5) Å. Besides, they not only represent structural novelty but also demonstrate controllable proton conduction properties. Catalysts 1 and 2 can catalyze cycloaddition of epoxides with CO₂ in a solvent-free system in conjunction with 1-ethyl-1-methylpyrrolidinium bromide.

A Rh-substituted polyoxometalate with an acetate-modified building block {As2W22O76(CH3COO)2}

The first example of Rh-substituted organic-inorganic hybrid arsenotungstate [H₂N(CH₃)₂]₈{[Na(H₂O)₄]NaAs₂W₂₂(CH₃COO)₂O₇₆ Rh₂(N(CH₃)₂)₂}·H₂O (1) synthesised in an aqueous solution by the conventional method is reported. Two [Rh(N(CH₃)₂)]³⁺ fragments are imbedded into the vacancy of the [NaAs₂W₂₂(CH₃COO)₂O₇₆]^15- unit by Rh-As bonds [2.439(1) Å], which are observed in POM chemistry for the first time.

Metal-metal bonds in polyoxometalate chemistry

Half a century ago, F. Albert Cotton emphasized the relevance of metal-metal bonding in the constitution of cluster materials. Based on his description, nanoscale polyoxometalates (POMs) normally would not be regarded as cluster materials. One reason is that metal-metal bonding is typically associated with inorganic systems featuring metal centres in low oxidation states, a feature that is not common for POMs. However, over the past decades, there have been increasing reports on POMs integrating different types of metal-metal bonding. This article conceptualises and reviews the area of metal-metal bonded POMs, and their preparation and physicochemical properties. Attention is given to the changes in the electronic structure of POMs, the emergence of covalent dynamics and its impact on the development of applications in catalysis, nanoswitches, donor-acceptor systems, electron storage materials and nanoelectronics (i.e., "POMtronics").

Electrochemically assisted fabrication of size-exclusion films of organically modified silica and application to the voltammetry of phospholipids

Modification of electrodes with nm-scale organically modified silica films with pores diameters controlled at 10- and 50-nm is described. An oxidation catalyst, mixed-valence ruthenium oxide with cyano crosslinks or gold nanoparticles protected by dirhodium-substituted phosophomolybdate (AuNP-Rh2PMo11), was immobilized in the pores. These systems comprise size-exclusion films at which the biological compounds, phosphatidylcholine and cardiolipin, were electrocatalytically oxidized without interference from surface-active concomitants such as bovine serum albumin. 10-nm pores were obtained by adding generation-4 poly(amidoamine) dendrimer, G4-PAMAM, to a (CH3)3SiOCH3 sol. 50-nm pores were obtained by modifying a glassy carbon electrode (GC) with a sub-monolayer film of aminopropyltriethoxylsilane, attaching 50-nm diameter poly(styrene sulfonate), PSS, spheres to the protonated amine, transferring this electrode to a (CH3)3SiOCH3 sol, and electrochemically generating hydronium at uncoated GC sites, which catalyzed ormosil growth around the PSS. Voltammetry of Fe(CN)63- and Ru(NH3)63+ demonstrated the absence of residual charge after removal of the templating agents. With the 50-nm system, the pore structure was sufficiently defined to use layer-by-layer electrostatic assembly of AuNP-Rh2PMo11 therein. Flow injection amperometry of phosphatidylcholine and cardiolipin demonstrated analytical utility of these electrodes.

Noble metals in polyoxometalate chemistry: palladium-containing derivatives of the monolacunary Keggin and Wells-Dawson tungstophosphates

We have prepared the three novel Pd(II)-containing tungstophosphates [Pd(2)(α-PW(11)O(39)H(0.5))(2)](9-) and two structural isomers of [Pd(2)(α(2)-P(2)W(17)O(61)H(n))(2)]((16-2n)-) via simple synthetic procedures and characterized their potassium salts by single-crystal X-ray diffraction, elemental analysis, and IR and multinuclear ((31)P and (183)W) NMR spectroscopy. This study sheds light on the long-standing question about the nature and structure of the actual products formed in the reaction of Pd(II) ions with monolacunary Keggin-type [α-XW(11)O(39)](n-) and Wells-Dawson-type [α(2)-P(2)W(17)O(61)](10-) heteropolytungstates.

Preparation and Electrocatalytic Application of Composites Containing Gold Nanoparticles Protected with Rhodium-Substituted Polyoxometalates

Substitution of a metal center of phosphomolybdate, PMo(12)O(40) (3-) (PMo(12)), or its tungsten analogue with dirhodium(II) and subsequent stabilization of gold nanoparticles, AuNPs, with Rh(2)PMo(11) is demonstrated. The AuNP-Rh(2)PMo(11) mediates oxidations but adsorbs too weakly for direct modification of electrode materials. Stability in quiescent solution was achieved by modifying glassy carbon (GC) with 3-aminopropyltriethoxysilane (APTES) and then electrostatically assembling AuNP-Rh(2)PMo(11). At GC|APTES|AuNP-Rh(2)PMo(11), cyclic voltammetry showed the expected set of three reversible peak-pairs for PMo(11) in the range -0.2 to 0.6 vs (Ag/AgCl)/V and the reversible Rh(II,III) couple at 1.0 vs (Ag/AgCl)/V. The presence of AuNPs increased the current for the reduction of bromate by a factor of 2.5 relative to that at GC|Rh(2)PMo(11), and the electrocatalytic oxidation of methionine displayed characteristics of synergism between the AuNP and Rh(II). To stabilize AuNP-Rh(2)PMo(11) on a surface in a flow system, GC was modified by electrochemically assisted deposition of a sol-gel with templated 10-nm pores prior to immobilizing the catalyst in the pores. The resulting electrode permitted determination of bromate by flow-injection amperometry with a detection limit of 4.0 × 10(-8) mol dm(-3).

The linkage between ribosomal crystallography, metal ions, heteropolytungstates and functional flexibility

Crystallography of ribosomes, the universal cell nucleoprotein assemblies facilitating the translation of the genetic-code into proteins, met with severe problems owing to their large size, complex structure, inherent flexibility and high conformational variability. For the case of the small ribosomal subunit, which caused extreme difficulties, post crystallization treatment by minute amounts of a heteropolytungstate cluster allowed structure determination at atomic resolution. This cluster played a dual role in ribosomal crystallography: providing anomalous phasing power and dramatically increased the resolution, by stabilization of a selected functional conformation. Thus, four out of the fourteen clusters that bind to each of the crystallized small subunits are attached to a specific ribosomal protein in a fashion that may control a significant component of the subunit internal flexibility, by "gluing" symmetrical related subunits. Here we highlight basic issues in the relationship between metal ions and macromolecules and present common traits controlling in the interactions between polymetalates and various macromolecules, which may be extended towards the exploitation of polymetalates for therapeutical treatment.

Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt Clusters

Five Co(II) silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K(20)[{(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)}(2)Co(H(2)O)(2)]47 H(2)O (1) consists of two {(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)} units connected by a {CoO(4)(H(2)O)(2)} group. In the chiral species K(7)[Co(1.5)(H(2)O)(7))][(gamma-SiW(10)O(36))(beta-SiW(8)O(30)(OH))Co(4)(OH)(H(2)O)(7)]36 H(2)O (2), a {gamma-SiW(10)O(36)} and a {beta-SiW(8)O(30)(OH)} unit enclose a mononuclear {CoO(4)(H(2)O)(2)} group and a {Co(3)O(7)(OH)(H(2)O)(5)} fragment. The two trinuclear Co(II) clusters present in 1 enclose a mu(4)-O atom, while in 2 a mu(3)-OH bridging group connects the three paramagnetic centers of the trinuclear unit, inducing significantly larger Co-L-Co (L=mu(4)-O (1), mu(3)-OH (2)) bridging angles in 2 (theta(av(Co-L-Co))=99.1 degrees ) than in 1 (theta(av(Co-L-Co))=92.8 degrees ). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2. The electrochemistry of 1 was studied in detail. The two chemically reversible redox couples observed in the positive potential domain were attributed to the redox processes of Co(II) centers, and indicated that two types of Co(II) centers in the structure were oxidized in separate waves. Redox activity of the seventh Co(II) center was not detected. Preliminary experiments indicated that 1 catalyzes the reduction of nitrite and NO. Remarkably, a reversible interaction exists with NO or related species. The hybrid tetranuclear complexes K(5)Na(3)[(A-alpha-SiW(9)O(34))Co(4)(OH)(3)(CH(3)COO)(3)]18 H(2)O (3) and K(5)Na(3)[(A-alpha-SiW(9)O(34))Co(4)(OH)(N(3))(2)(CH(3)COO)(3)]18 H(2)O (4) were characterized: in both, a tetrahedral {Co(4)(L(1))(L(2))(2)(CH(3)COO)(3)} (3: L(1)=L(2)=OH; 4: L(1)=OH, L(2)=N(3)) unit capped the [A-alpha-SiW(9)O(34)](10-) trivacant polyanion. The octanuclear complex K(8)Na(8)[(A-alpha-SiW(9)O(34))(2)Co(8)(OH)(6)(H(2)O)(2)(CO(3))(3)]52 H(2)O (5), containing two {Co(4)O(9)(OH)(3)(H(2)O)} units, was also obtained. Compounds 2, 3, 4, and 5 were less stable than 1, but their partial electrochemical characterization was possible; the electronic effect expected for 3 and 4 was observed.

Tetrahydroxy-p-benzoquinone as a Source of Polydentate O-Donor Ligands. Synthesis, Crystal Structure, and Magnetic Properties of the [Cu(bpy)(dhmal)]2 Dimer and the Two-Dimensional [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2]·16H2O Inorganic−Metalorganic Hybrid

The use of tetrahydroxy-p-benzoquinone as a slow source of dihydroxymalonato and oxalato ligands led to the isolation under open-air mild reaction conditions of five different compounds, two of them prepared for the first time: [Cu(bpy)(dhmal)]2 (1) and [{SiW12O40}{Cu2(bpy)2(H2O)(ox)}2].16H2O (5) (bpy, 2,2'-bipyridine; dhmal, dihydroxymalonate; ox, oxalate). A possible mechanism for the oxidation of the benzoquinone to give the croconate dianion, which undergoes further ring-opening oxidation to decompose into dihydroxymalonate and oxalate, is proposed. All compounds have been characterized by elemental analysis, thermogravimetry, infrared spectroscopy, and powder X-ray diffraction. Single-crystal X-ray diffraction, electron paramagnetic resonance, and magnetic susceptibility measurements have been performed for compounds 1 and 5. A complete band assignment of the experimental FT-IR spectra is given through comparison with the ones calculated using density functional theory (DFT). The neutral dimer 1 constitutes the first structurally characterized example of a transition metal-dhmal complex, and it contains two copper atoms bridged by two dihydroxymalonato ligands acting in a mu2-kappa3O,O',O":kappa1O coordination fashion, so that an equatorial-axial Cu2(mu2-O)2 rhomboid core is formed. On the other hand, the inorganic-metalorganic hybrid compound 5 shows a two-dimensional arrangement of Keggin polyanions linked by one of the Cu atoms of the oxalate cationic dimers to give layers parallel to the (10) plane, the remaining ox-Cu-bpy fragments acting as interlamellar separators. In both cases, magnetic and EPR results are discussed with respect to the crystal structure of the compounds and, for compound 1, also with respect to DFT calculations of the exchange coupling constant.

The geometry of the ribosomal polypeptide exit tunnel

The geometry of the polypeptide exit tunnel has been determined using the crystal structure of the large ribosomal subunit from Haloarcula marismortui. The tunnel is a component of a much larger, interconnected system of channels accessible to solvent that permeates the subunit and is connected to the exterior at many points. Since water and other small molecules can diffuse into and out of the tunnel along many different trajectories, the large subunit cannot be part of the seal that keeps ions from passing through the ribosome-translocon complex. The structure referred to as the tunnel is the only passage in the solvent channel system that is both large enough to accommodate nascent peptides, and that traverses the particle. For objects of that size, it is effectively an unbranched tube connecting the peptidyl transferase center of the large subunit and the site where nascent peptides emerge. At no point is the tunnel big enough to accommodate folded polypeptides larger than alpha-helices.

Experimental and Theoretical Study of the Regiospecific Coordination of RuII and OsII Fragments on the Lacunary Polyoxometalate [α-PW11O39]7-

New Ru(II) and Os(II) derivatives of the monovacant [alpha-PW(11)O(39)](7-) anion ([PW(11)O(39){M(DMSO)(3)(H(2)O)}](5-) (M = Ru (1), Os (2)) and [PW(11)O(39){Os(eta(6)-p-cym)(H(2)O)}](5-) (3)) have been synthesized and characterized. The binding mode of the d(6)-{M(II)L(3)(H(2)O)}(2+) moieties in these compounds is similar to that in the previously described [PW(11)O(39){Ru(eta(6)-p-cym)(H(2)O)}](5-) (4) complex: bidentate, on two nonequivalent oxygen atoms of the lacuna, leading to a loss of the C(s) symmetry of the parent anion, which thus plays the role of a prochiral bidentate ligand. The density functional theory (DFT) (B3PW91) computation of the lowest unoccupied molecular orbitals of the {ML(3)(H(2)O)}(2+) (M = Os, Ru; L(3) = fac-(DMSO)(3), eta(6)-C(6)H(6)) fragments reveals the similarities between their electrophilic properties. The origin of the regioselectivity of the grafting was investigated through a DFT (B3PW91) analysis of (i) the highest occupied molecular orbital of [alpha-PW(11)O(39)](7-) and (ii) the relative energies of the different potential regioisomers obtained by a bidentate grafting of the {ML(3)(H(2)O)}(2+) moiety onto the lacuna of [alpha-PW(11)O(39)](7-). The role of the water ligand in the stabilization of this peculiar structure was studied.

Unsymmetrical surface modification of a heteropolyoxotungstate via in-situ generation of monomeric and dimeric copper(ii) species

Unsymmetrical functionalization of a discrete alpha-{SiW12O40} Keggin with two heterometallic building blocks, a Cu(II) dimer and a Cu(II) monomer, results in the formation of [{Cu2(O2CMe)2(5,5'-dimethyl-2,2'-bipy)2}{Cu(5,5'-dimethyl-2,2'-bipy)2}SiW12O40] that displays interesting physical properties.

Novel Ti–O–Ti bonding species constructed in a metal-oxide cluster

The preparation and structural characterization of a novel Ti-O-Ti bonding complex constructed in the mono-lacunary alpha-Keggin polyoxometalate (POM), are described. The water-soluble, crystalline complex with a formula of K5H2[[{Ti(OH)(ox)}2(micro-O)](alpha-PW11O39)] x 13H2O 1 was prepared in 30.2% (0.60 g scale) yield in a 1 : 3 molar-ratio reaction of the tri-lacunary species of alpha-Keggin POM, Na9[A-PW9O34] x 19H2O, with the titanium(IV) source, K2TiO(ox)2 x 2H2O (H2ox = oxalic acid), in HCl-acidic solution (pH 0.08), and characterized by complete elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, solution (31P, 183W, 1H and 13C) NMR spectroscopy and X-ray crystallography. The complex was also obtained in 47.6% (0.81 g scale) yield in a 1 : 2 molar-ratio reaction of the mono-lacunary Keggin POM, K7[PW11O39] x 10H2O, with the anionic titanium(IV) complex under acidic conditions. The molecular structure of [[{Ti(OH)(ox)}2(micro-O)](alpha-PW11O39)]7- 1a, was successfully determined. This POM in the solid state is composed of one host (mono-lacunary site) and two guests (two octahedral Ti groups), in contrast to most titanium (IV)-substituted POMs consisting of one host and one guest. On the other hand, the 31P NMR measurements revealed that in aqueous solution this POM was present under a dissociation equilibrium which depends upon both temperature and pH.

The ruthenium(ii)-supported heteropolytungstates [Ru(dmso)3(H2O)XW11O39]6−(X = Ge, Si)

The novel Ru(II)-supported heteropolytungstates [Ru(dmso)(3)(H(2)O)XW(11)O(39)](6-)(X = Ge, Si) have been synthesized and characterized by single-crystal X-ray diffraction, multinuclear NMR ((183)W, (13)C, (1)H, (29)Si) and IR spectroscopy, elemental analysis and electrochemistry. The novel polyanion structure consists of a Ru(dmso)(3)(H(2)O) unit linked to a monolacunary [XW(11)O(39)](8-) Keggin fragment via two Ru-O-W bonds resulting in an assembly with C(1) symmetry. Polyanions 1 and 2 were synthesized by reaction of cis-Ru(dmso)(4)Cl(2) with [A-alpha-XW(9)O(34)](10-) in aqueous, acidic medium (pH 4.8). Tungsten-183 NMR of 1 leads to a spectrum with 11 peaks of equal intensity, indicating that the solid-state structure is preserved in solution. Electrochemistry studies revealed that 1 and 2 are stable in solution at least from pH 0 to 7, even in the presence of dioxygen. Their cyclic voltammetry patterns show mainly two two-electron reversible W-waves, those of the Si derivative 2 being located at slightly more negative potentials than those of the Ge derivative 1. The observed stability of 1 and 2 might be attributed to a stabilization of the Ru-center both by the strongly bound dmso ligands and the Keggin moiety. This stabilization drives the redox waves of Ru outside the accessible potential range. However, conditions were found to reveal, at least partially, the redox behavior of Ru in 1 and 2.

Preparation and characterization of new ruthenium and osmium containing polyoxometalates, [M(DMSO)3Mo7O24](4-) (M = Ru(II), Os(II)), and their use as catalysts for the aerobic oxidation of alcohols

A new heptamolybdate polyoxometalate structure containing ruthenium(II) or osmium(II) metal centers, [M(II)(DMSO)(3)Mo(7)O(24)](4-) (M = Ru, Os), was synthesized by reaction between (NH(4))(6)Mo(7)O(24) and cis-M(DMSO)(4)Cl(2). X-ray structure analysis revealed the complexes to contain a ruthenium/osmium center in a trigonal antiprismatic coordination mode bound to three DMSO moieties via the sulfur atom of DMSO and three oxygen atoms of the new heptamolybdate species. The heptamolybdate consists of seven condensed edge-sharing MoO(6) octahedra with C(2v) symmetry. Three Mo atoms are in classic type II octahedra with a cis dioxo configuration. Two Mo atoms are also type-II-like, but one of the short Mo-O bonds is associated with bridging oxygen atoms rather than terminal oxygen atoms. Two molybdenum atoms are unique in that they are in a trigonally distorted octahedral configuration with three short Mo-O bonds and two intermediate-long M-O bonds and one long Mo-O bond. The [M(II)(DMSO)(3)Mo(7)O(24)](4-) polyoxometalates were effective and in some cases highly selective catalysts for the aerobic oxidation of alcohols to ketones/aldehydes. The integrity of the polyoxometalate was apparently retained at high turnover numbers and throughout the reaction, and a variation of an oxometal type mechanism was proposed to explain the results.

[Mo5VMo7VIO30(BPO4)2(O3P-Ph)6]5-: a phenyl-substituted molybdenum(V/VI) boro-phosphate polyoxometalate

The title polyanion is the first hybrid borophosphate-phenylphosphonate polyoxometalate. It was structurally characterized as its imidazolium salt, (C(3)N(2)H(5))(5)[Mo(12)O(30)(BPO(4))(2)(O(3)P-Ph)(6)].H(2)O (monoclinic, P2(1)/c, a = 22.120(3) A, b = 13.042(2) A, and c = 32.632(4) A, beta = 101.293(3) degrees ), which was synthesized hydrothermally from imidazole, molybdenum oxide and metal, and boric, phosphoric, and phenylphosphonic acids. The anion is the second example of a new class of polyoxometalates that resemble Dawson anions but where the two pole caps of three edge-sharing MoO(6) octahedra in the latter are replaced by other units, in this case tetrahedral borate sharing corners with three phenylphosphonic groups, [(OB)(O(3)P-Ph)(3)]. The 12 molybdenum atoms forming the two equatorial belts of the cluster are of mixed-valence, five are Mo(V) and seven are Mo(VI), and the resulting five electrons are delocalized. Four of these electrons are paired according to the temperature dependence of the magnetic susceptibility. The new compound is soluble in a mixture of water and pyridine (in equal volumes) as well as in nitromethane, and the anions are intact in these solutions.

Heteropolymolybdates of phosphate, phosphonate, and phosphite functionalized by glycine

The novel, functionalized heteropolymolybdates [RPMo(6)O(21)(O(2)CCH(2)NH(3))(3)](2)(-) (R = OH, CH(3), C(2)H(5), H) have been synthesized and characterized by IR, (31)P NMR spectroscopy, and elemental analysis. Single-crystal X-ray analysis was carried out on K(2)[HOPMo(6)O(21)(O(2)CCH(2)NH(3))(3)].8.5H(2)O, which crystallizes in the orthorhombic system, space group Pnma, with a = 14.118(2) A, b = 20.660(3) A, c = 12.191(2) A, and Z = 4; K(2)[H(3)CPMo(6)O(21)(O(2)CCH(2)NH(3))(3)].8.5H(2)O, which crystallizes in the orthorhombic system, space group Pnma, with a = 14.1643(6) A, b = 20.8658(8) A, c = 12.2235(5) A, and Z = 4; and K(2)[HPMo(6)O(21)(O(2)CCH(2)NH(3))(3)].8H(2)O, which crystallizes in the orthorhombic system, space group Pnma, with a = 14.092(3) A, b = 20.696(2) A, c = 12.199(4) A, and Z = 4. We also report on the synthesis and characterization of the isostructural derivative K(2)[H(5)C(2)PMo(6)O(21)(O(2)CCH(2)NH(3))(3)]. The four title polyanions consist of an RP (R = OH, CH(3), C(2)H(5), H) hetero group surrounded by a ring of six MoO(6) octahedra sharing edges and corners alternatingly. Three glycine molecules are each bound to two edge-sharing Mo centers via their carboxylate functionality on the same side of the ring. The central phosphorus atom is located slightly above the plane of the six molybdenums, and its terminal R group is on the same side of the ring as the glycines. NMR studies show that the solid state structures of the title compounds are preserved in solution.

Polyoxomolybdates functionalized with phosphonocarboxylates

The novel, functionalized heteropolymolybdate [(O(2)CCH(2)PO(3))(2)Mo(5)O(15)](6-) (1) has been synthesized and characterized by IR and (31)P NMR spectroscopy and elemental analysis. Single-crystal X-ray analysis was carried out on Rb(4)KNa[(O(2)CCH(2)PO(3))(2)Mo(5)O(15)].H(2)O, which crystallizes in the monoclinic system, space group P2(1)/n, with a = 10.146(2) A, b = 13.704(3) A, c = 20.577(4) A, beta = 94.88(3) degrees, and Z = 4. The title polyanion consists of a ring of five MoO(6) octahedra with four edge junctions and one corner junction. This nonplanar arrangement is stabilized by two phosphonocarboxylate groups that are bound via their phosphonate functionalities on opposite sides of the ring. As a result the two dangling arms with their terminal carboxylate groups protrude away from the molybdenum-oxo framework in diametrically opposed directions. The solid-state structure of 1 is preserved in solution on the basis of NMR. We also report on the synthesis and characterization of the isostructural derivative [(O(2)CC(2)H(4)PO(3))(2)Mo(5)O(15)](6-) (2).