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The first examples of dimeric, di-Pt(II) -containing heteropolytungstates are reported. The two isomeric di-platinum(II)-containing 22-tungsto-2-phosphates [anti-Pt(II)2(α-PW11O39)2](10-) (1 a) and [syn-Pt(II)2(α-PW11O39)2](10-) (2 a) were synthesized in aqueous pH 3.5 medium using one-pot procedures. Polyanions 1 a and 2 a contain a core comprising two face-on PtO4 units, with a Pt⋅⋅⋅Pt distance of 2.9-3 Å. Both polyanions were investigated by single-crystal XRD, IR, TGA, UV/Vis, (31) P NMR, ESI-MS, CID-MS/MS, electrochemistry, and DFT. On the basis of DFT and electrochemistry, we demonstrated that the {Pt2(II)} moiety in 1 a and 2 a can undergo fully reversible two-electron oxidation to {Pt2(III)}, accompanied by formation of a single Pt-Pt bond. Hence we have discovered the novel subclass of Pt(III)-containing heteropolytungstates., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The Co7 (AlePy)2 polyoxometalate, which encloses a {(PW9 )2 Co(II) 7 } core covalently bound to two free aminopyridine groups through bisphosphonate ligands (AlePy), has been isolated. It can be used as a precursor, allowing the synthesis of heterometallic hybrid compounds, as illustrated by the characterization of cobalt/zinc (Co7 (AlePyZn)2 ), cobalt/palladium (Co7 (AlePyPd)2 ), and cobalt/platinum (Co7 (AlePyPt)2 ) species. A composite based on the water-insoluble precious metal-free Co7 (AlePyZn)2 compound and the low-cost carbon material Vulcan XC-72 has been selected as a cathode material (Co7 Zn/C) for oxygen reduction reaction studies. The electrocatalytic performances of the Co7 Zn/C hybrids were assessed at neutral and basic pH, showing that Co7 Zn/C exhibits high selectivity for the four-electron reduction of O2 . Moreover, its durability is superior to that of a commercial Pt/C catalyst with 20 % loading. Also, comparative studies performed in the presence of methanol have indicated that Co7 Zn/C has a much better tolerance to the crossover effect than Pt/C. Altogether, these results indicate for the first time that, even in neutral media, polyoxometalate/carbon composites can represent low-cost oxygen reduction catalysts that can function stably, for a long time, and with high performance., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of hybrid nickel bisphosphonate (BP) polyoxometalates (POMs) has been isolated. The complexes NaK-Ni7-Ale2 (Ale = [H2O3PC(C3H6NH2)(OH)PO3H2]) and NaNH4-Ni7-Ale2 are both made of two {PW9O34} fragments enclosing a heptanuclear Ni(II) core connected to two alendronate ligands. By pre-functionalising the alendronate moiety through the amino group, the naphthalene (napht) derivative Ni7-(AleNapht)2 and the compounds Ni7-(AlePy2 Ni)2 (py = pyridyl) and Ni7-(AleAc2Ni)2 (Ac = acyl) have been obtained. Compared with the NaK-Ni7-Ale2 species, these last two complexes contain two additional Ni(II) centres connected through two bis(2-pyridylmethyl)amine or two iminodiacetate groups, respectively. This results show that it is possible to functionalise the heptanuclear POM in a controlled manner. Quantification of the magnetic interactions in NaK-Ni7-Ale2 revealed that in the {Ni7} core, ferromagnetic interactions are predominant, with a S = 5 ground state. Magnetisation versus dc field sweeps on a single crystal of NaK-Ni7-Ale2 exhibited hysteresis at low temperature. (1)H and (31)P NMR studies in aqueous solution performed on NaK-Ni7-Ale2 and Ni7-(AleNapht)2 evidenced that the PW9/Ni7/bisphosphonate assembly is stable in solution. This was completed by (31)P magic angle spinning (MAS) investigations and confirmed by (1)H DOSY experiments. The electrochemistry of these compounds proceeds through two well-defined four-electron chemically reversible waves in a medium at pH 6. NaK-Ni7-Ale2 proved to be efficient for the electrocatalytic reduction of nitrate, nitrite and nitrous oxide. Remarkably, its electrocatalytic efficiency for nitrate reduction is approximately three times higher than those previously reported for POMs in a medium at pH >4 under the same potential. The catalytic properties of two representatives of the hybrid family were also examined. It is shown that these nickel bisphosphonate polyoxotungstates are pre-catalysts for the oxidation of alcohols into ketones or carboxylic acids, depending on the classes of alcohols considered, the stoichiometric oxidant used being H2O2. Noticeably, it has been found that an analogous cobalt bisphosphonate polyoxotungstate complex does not present any related activity, highlighting the crucial role of the 3d cations on the catalytic process., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Trapped in a noble cube: A novel family of noble metalates has been discovered in which a 3d metal ion M (M = Mn(II), Fe(III), Co(II), Cu(II), Zn(II)) is encapsulated by a 12 palladium-oxo cage {Pd(12)O(32)}, which is capped by eight phosphate groups. Such discrete nanocubes were further investigated by EPR spectroscopy, electrochemistry, and in homogeneous hydrogenation catalysis., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Wheely: For the first time and very unexpectedly, a rupture of the very stable {P(8)W(48)} wheel was observed in aqueous solution at pH 4 and 80 °C in the presence of Fe(III), Eu(III)/Gd(III), and H(2)O(2). This inorganic ring opening is unprecedented in polyoxometalate chemistry., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A green, facile, one-pot synthesis of well-defined Au NPs@POM-GNSs tricomponent nanohybrids is reported (POM stands for polyoxometalate and GNSs for graphene nanosheets). The synthesis is convenient, rapid and environmentally friendly. The POMs serve as both reducing, encapsulating molecules, and bridging molecules; this avoids the introduction of other organic toxic molecules. Characterization using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy analysis is performed, and the structure of the prepared nanohybrids of Au NPs@POM-GNSs is verified. Most importantly, the amperometric measurements show the Au NPs@POM-GNSs nanohybrids have high catalytic activity with good sensitivity, good long-term stability, wide linear range, low detection limit, and fast response towards H(2)O(2) detection for application as an enzyme-free biosensor. Transformation of the POMs during H(2)O(2) detection does not affect the catalytic activities of the nanohybrids. Thus, the synergistic effect of Au NPs and GNSs in the nanohybrids leads to the enhanced catalytic property., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of novel yttrium- and lanthanide-containing heteropolyoxopalladates have been prepared and isolated as hydrated sodium salts, Na(5)[X(III)Pd(II)(12)(AsPh)(8)O(32)]y H(2)O (X=Y (1), Pr (2), Nd (3), Sm (4), Eu (5), Gd (6), Tb (7), Dy (8), Ho (9), Er (10), Tm (11), Yb (12), Lu (13); y=15-27). The polyanions [X(III)Pd(II)(12)(AsPh)(8)O(32)](5-) consist of a cuboid framework of twelve Pd(II) ions with eight phenylarsonate heterogroups located at the vertices and a central guest ion X. The compounds 1-13 have been prepared in a simple one-pot self-assembly reaction of Pd(CH(3)COO)(2), phenylarsonic acid and the respective salt of the element X in 0.5 M aqueous sodium acetate solution (pH 6.9), and characterized in the solid state by single-crystal X-ray diffraction, elemental and thermogravimetric (TGA) analyses, and IR spectroscopy. It was demonstrated that small, medium, and also large lanthanide ions can be incorporated in the center of the novel heteropolypalladate [X(III)Pd(II)(12)(AsPh)(8)O(32)](5-). The Ln-O bond lengths follow the expected trend decreasing from left to right in the lanthanide series. This indicates that the {Pd(II)(12)O(32)} shell can adjust to the coordination requirements of the encapsulated guest cation. Compounds 3 and 5 were selected for electrochemical studies. Their cyclic voltammetry in a lithium acetate buffer at pH 5.9 showed a Pd(0) deposition process on the glassy carbon electrode surface. Coulometry indicated that all Pd(II) centers were reduced to Pd(0). The film was stable and could be taken out of the deposition medium and characterized in pure pH 5.9 buffer. Magnetic susceptibility and EPR measurements were carried out on 5 and 6. The former was confirmed to be diamagnetic and the latter strongly paramagnetic with a S=7/2 ground state. DFT calculations for some of the polyoxometalates have been also performed.

Two new compounds based on O(3)PCH(2)PO(3)(4-) ligands and {Mo(V)(2)O(4)} dimeric units have been synthesized and structurally characterized. The dodecanuclear Mo(V) polyoxomolybdate species in (NH(4))(18)[(Mo(V)(2)O(4))(6)(OH)(6)(O(3)PCH(2)PO(3))(6)] x 33 H(2)O (1) is a cyclohexane-like ring in a chair conformation with pseudo S(6) symmetry. In the solid state, the wheels align side by side, thus delimiting large rectangular voids. The hexanuclear anion in Na(8)[(Mo(V)(2)O(4))(3)(O(3)PCH(2)PO(3))(3)(CH(3)AsO(3))] x 19 H(2)O (2) has a triangular framework and encapsulates a methylarsenato ligand. (31)P 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 CH(3)AsO(3)(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 Pt(0) and Pd(0) 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 POM to remember: Hexanuclear Fe(III) polyoxometalate (POM) single-molecule magnets (see structure) can be noncovalently assembled on the surface of single-wall carbon nanotubes. Complementary characterization techniques (see TEM image and magnetic hysteresis loops) demonstrate the integrity and bistability of the individual molecules, which could be used to construct single-molecule memory devices.

The 16-Fe(III)-containing 48-tungsto-8-phosphate [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) (1) has been synthesised and characterised by IR and ESR spectroscopy, TGA, elemental analyses, electrochemistry and susceptibility measurements. Single-crystal X-ray analyses were carried out on Li(4)K(16)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)]66 H(2)O2 KCl (LiK-1, orthorhombic space group Pnnm, a=36.3777(9) A, b=13.9708(3) A, c=26.9140(7) A, and Z=2) and on the corresponding mixed sodium-potassium salt Na(9)K(11)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)].100 H(2)O (NaK-1, monoclinic space group C2/c, a=46.552(4) A, b=20.8239(18) A, c=27.826(2) A, beta=97.141(2) degrees and Z=4). Polyanion 1 contains--in the form of a cyclic arrangement--the unprecedented {Fe(16)(OH)(28)(H(2)O)(4)}(20+) nanocluster, with 16 edge- and corner-sharing FeO(6) octahedra, grafted on the inner surface of the crown-shaped [H(7)P(8)W(48)O(184)](33-) (P(8)W(48)) precursor. The synthesis of 1 was accomplished by reaction of different iron species containing Fe(II) (in presence of O(2)) or Fe(III) ions with the P(8)W(48) anion in aqueous, acidic medium (pH approximately 4), which can be regarded as an assembly process under confined geometries. One fascinating aspect is the possibility to model the uptake and release of iron in ferritin. The electrochemical study of 1, which is stable from pH 1 through 7, offers an interesting example of a highly iron-rich cluster. The reduction wave associated with the Fe(III) centres could not be split in distinct steps independent of the potential scan rate from 2 to 1000 mV s(-1); this is in full agreement with the structure showing that all 16 iron centres are equivalent. Polyanion 1 proved to be efficient for the electrocatalytic reduction of NO(x), including nitrate. Magnetic and variable frequency EPR measurements on 1 suggest that the Fe(III) ions are strongly antiferromagnetically coupled and that the ground state is tentatively spin S=2.

The dititanium-containing 19-tungstodiarsenate(III) [Ti(2)(OH)(2)As(2)W(19)O(67)(H(2)O)](8-) (1) has been synthesized and characterized by IR, TGA, elemental analysis, electrochemistry, and catalytic studies. Single-crystal X-ray analysis was carried out on Cs(8)[Ti(2)(OH)(2)As(2)W(19)O(67)(H(2)O)].2CsCl.12H(2)O (Cs-1), which crystallizes in the monoclinic system, space group P2(1)/m, with a=12.7764(19), b=19.425(3), c=18.149(3) A, beta=110.234(3) degrees, and Z=2. Polyanion 1 comprises two (B-alpha-As(III)W(9)O(33)) Keggin moieties linked through an octahedral {WO(5)(H(2)O)} fragment and two unprecedented square-pyramidal {TiO(4)(OH)} groups, leading to a sandwich-type structure with nominal C(2v) symmetry. Synthesis of 1 was accomplished by reaction of TiOSO(4) and K(14)[As(2)W(19)O(67)(H(2)O)] in a 2:1 molar ratio in aqueous, acidic medium (pH 2). Polyanion 1 could also be isolated as a tetra-n-butyl ammonium (TBA) salt, {(n-C(4)H(9))(4)N}(5)H(3)[Ti(2)(OH)(2)As(2)W(19)O(67)(H(2)O)] (TBA-1). TBA-1 was studied by cyclic voltammetry in acetonitrile (MeCN) solutions containing 0.1 M LiClO(4) and compared with the results obtained with Cs-1 in aqueous media. In MeCN, the Ti(IV) and W(VI) waves could not be separated distinctly. An important adsorption phenomenon on the glassy carbon working electrode was encountered both in cyclic voltammetry and in controlled potential electrolysis and was confirmed by Electrochemical Quartz Crystal Microbalance (EQCM) studies on a carbon film. TBA-1, dissolved in MeCN, reacts with H(2)O(2) to give peroxo complexes stable enough for characterization by UV-visible spectroscopy, cyclic voltammetry, and EQCM. TBA-1 shows high catalytic activity (TOF=11.3 h(-1)) in cyclohexene oxidation with aqueous H(2)O(2) producing products typical of a heterolytic oxidation mechanism. The stability of TBA-1 under turnover conditions was confirmed by using IR, UV-visible spectroscopy as well as cyclic voltammetry.

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.

The electrochemical behavior of the ball-shaped heteropolytungstates [[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12)(A-XW(9)O(34))(12)](36-) (X=P, 1; As, 2) was examined in aqueous electrolytes by redissolution of their respective mixed cesium-sodium salts Cs(14)Na(22)[[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12) (A-PW(9)O(34))(12)]149 H(2)O (Cs(14)-1) and Cs(14)Na(22)[[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12)(A-AsW(9)O(34))(12)]149 H(2)O (Cs(14)-2). In the studied media, Cs(14)-2 is readily soluble in contrast to the significantly less soluble Cs(14)-1. The solubility of Cs(14)-1 is increased by the presence of Li(+) ions in solution. Gel filtration studies with 1 and 2 rule out a decay of the dodecameric spherical assemblies to Keggin-based monomers on the timescale of the experiment. By UV/Vis spectroscopy and cyclic voltammetry, 2 was found to be significantly less stable than 1 and both polyanions also show rather different decomposition pathways. Polyanion 1 collapses first into Keggin-type monomers which might contain the trilacunary [A-alpha-PW(9)O(34)](9-). The final monomeric species obtained from 1 appears to be very similar to [PW(11)O(39)](7-), which is the final transformation product of [A-alpha-PW(9)O(34)](9-) in the same media. In contrast, 2 does not seem to follow an analogous transformation pathway as that of the trilacunary [A-alpha-AsW(9)O(34)](9-). Importantly, stabilization of 1 is observed in chloride media. The fairly long-term stability of 1 in 1 M LiCl, pH 3, has allowed for its electrochemical study to be carried out. The solid-state cyclic voltammogram of 1 entrapped in a carbon paste electrode shows the same characteristics as 1 dissolved in chloride solutions, thus supporting the conclusion that the polyanion is stable in these environments. Controlled potential coulometry on 1 indicates that the number of electrons consumed in the first wave is larger than twenty. To our knowledge, 1 constitutes the first example of a molecule that can take up such a large number of electrons resulting in a chemically reversible W-wave. These properties show promise for future fundamental and applied studies. Polyanion 1 is also efficient in the electrocatalytic reduction of NO(x), including nitrate. Finally, a remarkable interaction was found between 1 and NO, a highly promising feature for biomimetic applications.