Search

We report on the synthesis, structure, and physicochemical characterization of the first three examples of neutral palladium‐oxo clusters (POCs). The 16‐palladium(II)‐oxo cluster [Pd16O24(OH)8((CH3)2As)8] (Pd16) comprises a cyclic palladium‐oxo unit capped by eight dimethylarsinate groups. The chloro‐derivative [Pd16Na2O26(OH)3 Cl3 ((CH3)2 As)8] (Pd16Cl) was also prepared, which forms a highly stable 3D supramolecular lattice via strong intermolecular interactions. The 24‐palladium(II)‐oxo cluster [Pd24O44(OH)8((CH3)2As)16] (Pd24) can be considered as a bicapped derivative of Pd16 with a tetra‐palladium‐oxo unit grafted on either side. The three compounds were fully characterized 1) in the solid state by single‐crystal and powder XRD, IR, TGA, and solid‐state 1H and 13C NMR spectroscopy, 2) in solution by 1H, 13C NMR and 1H DOSY spectroscopic methods, and 3) in the gas phase by electrospray ionization mass spectrometry (ESI‐MS)., The first three examples of neutral palladium‐oxo clusters (POCs), Pd16, Pd16Cl, and Pd24, were prepared by simple open‐pot, room‐temperature reactions of palladium(II) salts in sodium dimethylarsinate aqueous solutions. The dimethylarsinate capping groups act as bidentate, monoanionic ligands for the various palladium‐oxo cores. The three POCs were fully characterized in the solid, solution, and gaseous states by a multitude of physicochemical techniques.

We report on the disparity in the assembly behavior of four types of nano-sized macroions induced by isotopic substitution of protium (H) to deuterium (D) in solvents. Macroions with modest charge density can self-assemble into single-layer, hollow, spherical "blackberry"-type structures, with larger assembly sizes representing stronger attractions among the macroions. Kinetically, all assembly processes become slower in D2 O than in H2 O. Thermodynamically, the polyoxometalate {SrPd12 }, the uranium cage {U60 } with alkali metal counterions, and the metal-organic cationic cage {Pd12 L24 } demonstrate similar assembly sizes in both H2 O and D2 O, whereas the metal oxide cluster {Mo72 Fe30 } as a weak acid shows an unusually large assembly size in H2 O-suggesting a stronger contribution from the hydrogen bonding in the last case.

The 36‐NiII‐containing 54‐tungsto‐6‐silicate, [Ni36(OH)18(H2O)36(SiW9O34)6]6− (Ni36 ) was synthesized by a simple one‐pot reaction of the Ni2‐pivalate complex [Ni2(μ‐OH2)(O2CCMe3)4(HO2CCMe3)4] with the trilacunary [SiW9O34]10− polyanion precursor in water and structurally characterized by a multitude of physicochemical techniques including single‐crystal XRD, FTIR, TGA, elemental analysis, magnetic and electrochemical studies. Polyanion Ni36 comprises six equivalent {NiII 6SiW9} units which are linked by Ni−O−W bridges forming a macrocyclic assembly. Magnetic studies demonstrate that the {Ni6} building blocks in Ni36 remain magnetically intact while forming a hexagonal ring with antiferromagnetic exchange interactions between adjacent {Ni6} units. Electrochemical studies indicate that the first reduction is reversible and associated with the WVI/V couple, whereas the second reduction is irreversible attributed to the NiII/0 couple., The 36‐NiII‐containing 54‐tungsto‐6‐silicate, [Ni36(OH)18(H2O)36(SiW9O34)6]6− (Ni36 ) was discovered and shown to contain more nickel centers than any other polyoxometalate (POMs) known to date. Polyanion Ni36 comprises six equivalent {NiII 6SiW9} units which are linked by Ni−O−W bridges forming a macrocyclic assembly. Magnetic studies indicate antiferromagnetic communication between the six {Ni6} subunits. Electrochemical studies indicate that the first reduction is reversible and associated to the WVI/V couple while the second reduction is irreversible and associated to the NiII/0 couple.

The palladium(II)-containing 40-tungsto-4-arsenate(III) [Pd2Na2KAs4W40O140(H2O)](21-) (1a) was synthesized by reaction of PdSO4 with the cryptate heteropolyanion [As4W40O140](28-) in potassium acetate buffer. The title compound was characterized by single-crystal XRD, IR, TGA, and elemental analysis.

Three types of macroanion-countercation interactions in dilute solution, decided by the strength of electrostatic attraction and the change of hydration shells are reported: minor interaction between macroanions [MO8 Pd12 (SeO3 )8 ]6- (M=Zn2+ or Ni2+ ) and monovalent cations (Na+ , K+ , Rb+ , Cs+ ), leaving their hydration shells intact (solvent-separated ion-pairs); strong binding between macroanions and divalent cations (Sr2+ , Ba2+ ) to form solvent-shared ion-pairs with partial dehydration; very strong electrostatic attraction between macroanions and Y3+ ion with contact ion-pairs formation by severely breaking their original hydration shells and forming new ones. In addition, divalent cations can help the macroanions self-assemble into hollow spherical blackberry structures through counterion-mediated attraction, whereas macroanions with mono- or trivalent cations only stay as discrete ions due to either weak interaction or a small number of bound countercations.

In the present study electrostatically-driven pH responsive supramolecular, self-assembled hydrogels of the trilacunary Wells-Dawson-type 15-tungsto-2-phosphate polyanion [P2W15O56]12− (P2W15) and polyethyleneimine were prepared. Crosslinking was achieved through electrostatic interactions between cationic polyethyleneimine and P2W15. The pH responsiveness was induced by acrylic acid. Benzoyl peroxide was used as an initiator, for initiating the polymerization reaction, anchoring polyacrylic acid on the polyethyleneimine skeleton. The prepared sea-green color hydrogels were characterized by FT-IR, SEM, XRD and thermal analysis (TGA-DSC). The swelling index, P2W15 release studies and pH responsive properties of the developed supramolecular hydrogels were evaluated at pH 1.2 and 7.4, showing maximum swellability and release characteristics at pH 7.4. For determining the P2W15 release mechanism different mathematical models such as zero order, first order, Higuchi model and Krosmeyer-Peppas models were applied and the results showed that embedded P2W15 release follows zero-order kinetics. The cytotoxicity results showed that naked and embedded P2W15 exhibited dose-dependent cytotoxicity against cancer cell lines (MCF-7; Hela) with minimal effects on normal cells (Vero). The hydrogels developed through electrostatic interactions exhibited desirable qualities of a drug delivery system that can be used for the delivery of the embedded polyanion.

The four 18-tungsto-2-arsenates(III) [MII(H2O)(TiIVO)2(α-AsIIIW9O33)2]12– [M = Co (CoTi2), Ni (NiTi2), Cu (CuTi2), Zn (ZnTi2)] were rationally synthesized by treating the respective divalent metal ions with the monolacunary, dititanium(IV)-containing polyanion precursor [(TiIVO)2(α-AsIIIW9O33)2]14– (Ti2) in aqueous solution. All four polyanions are isostructural and correspond to dimers with two Ti4+ and one M2+ ion sandwiched between two [α-AsIIIW9O33]9– units. The compounds were characterized in the solid state by single-crystal XRD, infrared spectroscopy, thermogravimetric analysis, and elemental analysis and in solution by UV/Vis and NMR spectroscopy as well as electrochemistry. Variable-temperature magnetic susceptibility and variable-field magnetization characterization of the paramagnetic derivatives indicate antiferromagnetic interactions between nearest neighbors in the solid state. The resolved hyperfine structure obtained from multifrequency EPR measurements on CuTi2 (which exhibits a Jahn–Teller effect) in the solid state lead us to assign the ground state mainly to the Cu dx²–y² orbital. Despite the fact that the four polyanions are isostructural and have the same overall negative charge, the cyclic voltammetric patterns featuring their chemically reversible reduction waves display distinct features. Electrocatalytic studies demonstrate that the activities of the polyanions towards nitrate reduction are strikingly influenced by the nature of the substituent metal ion.

We introduce the class of discrete silver(I)-palladium(II)-oxo nanoclusters with the preparation of {Ag4Pd13} and {Ag5Pd15}. Both polyanions represent the first examples of noble metal-capped polyoxo-noble-metalates in a fully inorganic assembly, featuring an unprecedented host–guest mode containing hetero- and homometallic Ag–Pd and Ag–Ag bonding interactions. Comprehensive theoretical calculations suggest that the Ag–Pd metallic bonds originate partially from surface confinement of AgI guest ions onto the anionic polyoxopalladate host that is induced by strong electrostatic forces. This work opens the field of fully inorganic silver-palladium-oxo nanoclusters, which can be considered as discrete mixed noble metal precursors for the formation of monodisperse core–shell nanoparticles, with high relevance for catalysis.

Die beiden diskreten Silber(I)-Palladium(II)-Oxo-Nanocluster {Ag4Pd13} und {Ag5Pd15} sind die ersten Beispiele von edelmetallverkappten Polyoxoedelmetallaten mit einem neuartigen Wirt-Gast-Bindungsmodus, der hetero- und homometallische Ag-Pd- und Ag-Ag-Wechselwirkungen beinhaltet. Umfassende theoretische Studien deuten darauf hin, dass die Ag-Pd-Metallbindungen teilweise von einem Polyanion-Oberflacheneffekt auf die AgI-Gastionen herruhren, der durch starke elektrostatische Krafte induziert wird. Diese Arbeit eroffnet ein Gebiet komplett anorganischer Silber-Palladium-Oxo-Nanocluster, die als Vorstufen fur die Bildung monodisperser Kern-Schale-Nanopartikel angesehen werden konnen, welche eine hohe Relevanz im Bereich der Katalyse haben.

The effect of cations in a reaction mixture for the preparation of the Preyssler-Jeannin-Pope type 30-tungsto-5-phosphate [P5W30O110Na]14– is investigated. Reaction of phosphate and tungstate with a P/W ratio of ca. 3.9 in an acidic aqueous solution without cations selectively leads to the Dawson-type 18-tungsto-2-phosphate, [P2W18O62]6–. Amongst all the alkali cations, only Na+ allows formation of the Preyssler-type polyanion [P5W30O110Na]14–, with an encapsulated Na+ ion, and the product yield can be improved by increasing Na+ amount. The presence of Li+ ions instead results in the Dawson-type polyanion [P2W18O62]6–, whereas K+, Rb+, and Cs+ selectively result in the Keggin-type polyanion [PW12O40]3–. An improved synthetic procedure for the Na+-encapsulated Preyssler-ion leading to a higher isolated yield is presented. Furthermore, addition of Ca2+ and Bi3+ compounds allows formation of the Ca2+- and Bi3+-encapsulated Preyssler-type polyanions, [P5W30O110Ca]13– and [P5W30O110Bi]12–, respectively. Furthermore, single-crystal XRD structure of the Bi3+-encapsulated Preyssler-type polyanions, [P5W30O110Bi]12–, is presented for the first time.

A family of three sandwich-type, phenylantimony(III)-containing tungstoarsenates(III), [(PhSb(III) ){Na(H2 O)}As(III) 2 W19 O67 (H2 O)](11-) (1), [(PhSb(III) )2 As(III) 2 W19 O67 (H2 O)](10-) (2), and [(PhSb(III) )3 (B-α-As(III) W9 O33 )2 ](12-) (3), have been synthesized by one-pot procedures and isolated as hydrated alkali metal salts, Cs3 K3.5 Na4.5 [(PhSb(III) ){Na(H2 O)}As(III) 2 W19 O67 (H2 O)]⋅41H2 O (CsKNa-1), Cs4.5 K5.5 [(PhSb(III) )2 As(III) 2 W19 O67 (H2 O)]⋅35H2 O (CsK-2), and Cs4.5 Na7.5 [(PhSb(III) )3 (B-α-As(III) W9 O33 )2 ]⋅42H2 O (CsNa-3). The number of incorporated {PhSb(III) } units could be selectively tuned from one to three by careful control of the reaction parameters. The three compounds were characterized in the solid state by single-crystal XRD, IR spectroscopy, and thermogravimetric analysis. The aqueous solution stability of sandwich polyanions 1-3 was also studied by multinuclear ((1) H, (13) C, (183) W) NMR spectroscopy. Effective inhibitory activity against six different kinds of bacteria was identified for all three polyanions, for which the activity increased with the number of incorporated {PhSb(III) } groups.

4-(Trifluoromethyl)pyrimidin-2(1H)-ones react with trimethylsilyl cyanide in the presence of a tertiary amine catalyst to give Michael-like 1,4-conjugate hydrocyanation adducts exclusively at the 3,6-positions. The resulting 2-oxo-6-(trifluoromethyl)-1,2,3,4-tetrahydropyrimidine-4-carbonitriles have been used to synthesize new trifluoromethylated 4,5-dihydroorotic acid analogues and their esters in racemic as well as enantiopure forms by a chiral auxiliary approach. The orthogonal intramolecular C–F···C=O interaction between the fluorine atom of the CF3 group and the carbon atom of the ester group observed in the crystal state may stabilize the sterically unfavourable conformation of the methyl 2-oxo-6-(trifluoromethyl)hexahydropyrimidine-4-carboxylate molecule with axially oriented substituents.

Die drei neuartigen, diskreten Palladium(II)-Oxocluster [CaPd12O8(PhAsO3)8]6− (CaPd12), [SrPd12O6(OH)3(PhAsO3)6(OAc)3]4− (SrPd12) und [BaPd15O10(PhAsO3)10]8− (BaPd15), bei denen die Erdalkalimetallionen im Innern einer kapselformigen Struktur vorliegen, wurden hergestellt und mit verschiedenen physikochemischen Methoden in Losung und im Festkorper charakterisiert. Die Ergebnisse offenbaren einen strukturdirigierenden Templateffekt des jeweiligen Alkalimetallions, dessen Grose die Anordnung der PdII-Oxo-Schale bestimmt. Von besonderer Bedeutung ist der prazedenzlose Cluster SrPd12, der eine offenschalige Struktur aufweist und eine Strategie fur den gezielten Entwurf von neuen Klassen von Polyoxoedelmetallaten aufzeigt. Der ungewohnliche Acetat-Wasser-Ligandenaustausch in SrPd12 macht diesen Cluster ferner zu einem vielversprechenden Kandidaten fur die Edelmetall-basierte Katalyse.

The three novel, discrete palladium(II)-oxo clusters [CaPd12O8(PhAsO3)8](6-) (CaPd12), [SrPd12O6(OH)3(PhAsO3)6(OAc)3](4-) (SrPd12), and [BaPd15O10(PhAsO3)10](8-) (BaPd15) encapsulating alkaline earth metal ions were prepared and fully characterized by a multitude of solution and solid-state physicochemical techniques. We have discovered a structure-directing template effect induced by the respective size of the alkaline earth guest ion, which determines the detailed condensation arrangement of the peripheral Pd(II)-oxo shell. The unprecedented SrPd12 with an open-shell type structure is of particular importance and reflects a successful strategy for deliberate design of new structural classes of polyoxo-noble-metalates. Furthermore, the unusual acetate-water ligand exchange phenomenon renders SrPd12 as a promising candidate for noble-metal-based catalysis.

The solution structure of the two presently known polyoxoaurates, [Au4As4O20]8– (Au4As4) and [Au4Se4O16]4– (Au4Se4), was elucidated by a combination of time-dependent density-functional-theory (TD-DFT) calculations, experimental UV/Vis spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The TD-DFT-predicted electronic spectra for molecular models including different numbers of counterions, along with the main Au4As4 and Au4Se4 structural motifs, were analyzed and compared with the experimental UV/Vis spectra of the two polyanions. The performed analysis revealed important structural differences between the arsenate and the selenite derivatives in aqueous solution. For the selenite oxoaurate, the bare Au4Se4 polyanion itself shows very good agreement between predicted and experimental excitation energies. In contrast, the solution state of the arsenate oxoaurate appears to be best described by a dimeric assembly of the type [Na5Au8As8O40]11– (Na5Au8As8) with a stoichiometry and structure very similar to those reported for the solid state. Indirect experimental evidence that Na5Au8As8 is the dominant species in aqueous solution is provided by ESI-MS measurements. Our work demonstrates that the combination of experimental UV/Vis spectroscopy and TD-DFT calculations complemented with electrospray mass spectrometry may serve as an alternative strategy for rationalizing the solution chemistry of polyoxometalates, which cannot be studied by conventionally used spectroscopic techniques, such as NMR or EPR spectroscopy.

The mono-lanthanide-containing [Ln(H2O)4Sb2W21O72(OH)]10– (Ln = Yb (1), Lu (2)), and the di-lanthanide-containing [Ln2(H2O)8Sb2W20O70)]8– (Ln = Yb (3), Lu (4), Y (5)) have been synthesized in aqueous-acidic media and characterized in the solid state. Polyanions 1 and 2 were prepared by reaction of Ln3+ ions with [Sb2W22O74(OH)2]12– (Sb2W22), whereas 3–5 were prepared by using the trilacunary 9-tungstoantimonate(III) [B-α-SbW9O33]9– (SbW9). Polyanions 1–5 crystallized as sodium salts in the triclinic system, space group P. All compounds were characterized in the solid state by FTIR, single-crystal XRD, TGA, and elemental analysis. Polyanions 1–5 contain the lacunary [Sb2W20O70]14– unit (Sb2W20), which is coordinated to either a lanthanide and a tungsten ion, leading to a structure with Cs symmetry in polyanions 1 and 2, or to two lanthanide ions, leading to a structure with idealized C2h symmetry, in polyanions 3–5.

The inhibition of the α-glucosidase enzyme plays an important role in the treatment of diabetes mellitus. We have established a highly sensitive, fast, and convenient CE method for the characterization of the enzyme and inhibition studies of α-glucosidase inhibitors. The separation conditions were optimized; the pH value and concentration of the borate-based separation buffer were optimized in order to achieve baseline separation of p-nitrophenyl-α-d-glucopyranoside and p-nitrophenolate. The optimized method using 25 mM tetraborate buffer, pH 9.5, was evaluated in terms of repeatability, LOD, LOQ, and linearity. The LOD and LOQ were 0.32 and 1.32 μM for p-nitrophenyl-α-d-glucopyranoside and 0.83 and 3.42 μM for p-nitrophenolate, respectively. The value of the Michaelis–Menten constant (Km) determined for the enzyme is 0.61 mM, which is in good agreement with the reported data. The RSDs (n = 6) for the migration time was 0.67 and 1.83% for substrate and product, respectively. In the newly established CE method, the separation of the reaction analytes was completed in

A family of {Ru(arene)}2+-containing heteropolytungstates of general formula [{Ru(L)}2(α-XW11O39)2WO2]m– (L = benzene, p-cymene; X = GeIV, SiIV, m = 10; X = BIII, m = 12) has been prepared in aqueous acidic medium (pH ≈ 4). The 1:1 interaction of [Ru(C6H6)Cl2]2 or [Ru(p-cymene)Cl2]2 with [β2-GeW11O39]8– led to the formation of [{Ru(benzene)}2(GeW11O39)2WO2]10– (1) and [{Ru(p-cymene)}2(GeW11O39)2WO2]10– (2), respectively. Replacing [β2-GeW11O39]8– by [α-SiW11O39]8– resulted in [{Ru(benzene)}2(SiW11O39)2WO2]10– (3) and [{Ru(p-cymene)}2(SiW11O39)2WO2][SiW12O40]0.512– (4), respectively. The reaction of [α-HBW11O39]8– with the respective {Ru(arene)}2+-containing precursors resulted in polyanions [{Ru(benzene)}2(HBW11O39)2WO2]10– (5) and [{Ru(p-cymene)}2(HBW11O39)2WO2]10– (6), respectively. Single-crystal XRD analysis of the hydrated salts of 1–6 revealed that these species comprise two Keggin fragments, [{Ru(L)}α-XW11O39]6– (L = benzene, p-cymene; X = GeIV, SiIV) for polyanions 1–4 and [{Ru(L)}α-HBW11O39]6– (L = benzene, p-cymene) for 5 and 6, connected via a cis-dioxo {WO2}2+ unit. In addition, the heteropolytungstates were characterized by thermogravimetric analysis, IR spectroscopy, elemental analysis, and solution electrochemical studies.

The two isomeric compounds K1.5(Me2NH2)8.5 [anti-PtII2 (α-PW11O39)2]·28H2O (I) and K1.5(Me2NH2)8.5 [syn-PtII2 (α-PW11O39)2]·18H2O (II) are obtained from an aqueous mixture of K7[α-PW11O39], K2PtCl4, and HCl (pH 4.0, 80 °C, 18—20 h) followed by addition of Me2NH2Cl (15 and 5% yield for (I) and (II), respectively).

Single crystals of Na39[{Na(H2O)6} Eu12(OH)12(H2O)18Ge2 (GeW10O38)6]·159H2O (I), Na37[{Na(H2O)6} Gd12(OH)6(H2O)24Ge (GeW10O38)6]·129H2O (II), and Na36 [{(H2O)6}Dy12(H2O)24 (GeW10O38)6]·122H2O (III) are prepared by slow crystallization from a solution containing equimolar amounts of LnCl3 (Ln: Eu, Gd, Dy) and Na10[α-GeW9O34] and NaCl at pH 5 (50 °C, 30 min; 23%, 20%, and 21% yield, resp.).

Compounds (IV) and (VII) are characterized in the solid state by single crystal XRD and FTIR spectroscopy, and in solution by UV/VIS and NMR spectroscopy and electrochemical measurements.

Polyoxometallate, die Edelmetallionen wie Ruthenium, Osmium, Rhodium, Palladium, Platin, Silber und Gold enthalten, bilden eine strukturell reichhaltige Klasse von Verbindungen. Hierzu gehoren sowohl klassische Heteropolyanionen (Vanadate, Molybdate, Wolframate), in denen die Edelmetalle als Heteroatome vorliegen, als auch die erst kurzlich entdeckte Klasse der Polyoxometallate mit Edelmetallen als “Addenda”-Atomen. Der Schwerpunkt dieses Aufsatzes liegt auf Komplexen, die in Losung als diskrete Molekule vorliegen und somit von Interesse fur zukunftige Synthesen und Entwicklungen in der Reaktivitat sind und potenzielle Anwendungen haben, z. B. in der Katalyse und den Nanowissenschaften.

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.

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.

Ruthenium(III)-substituted α-Keggin-type silicotungstates with pyridine-based ligands, [SiW(11)O(39)Ru(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 [SiW(11)O(39)Ru(III)(H(2)O)](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 (1)H NMR spectroscopy, elemental analysis, titration, and X-ray absorption near-edge structure (XANES) analysis (Ru K-edge and L(3)-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.

Polyoxometalates (POMs) are a remarkable class of inorganic compounds with enormous structural and compositional diversity and potential applications in various fields, such as catalysis, analytical chemistry, magnetism, nanotechnology, and medicine. In particular lacunary heteropolytungstates of the Keggin and Wells–Dawson type are useful inorganic, diamagnetic ligands allowing for encapsulation of various multinuclear metal-oxo assemblies. Examples of such kinds of structurally, catalytically, and magnetically interesting POMs are the manganese-containing derivative {Mn14W36}, [2a] the iron-containing derivatives {Fe9W12}, [3a] {Fe13W36}, [3b,c] {Fe16W48}, [3d] {Fe28W48}, [3e] the nickel-containing derivatives {Ni9W27}, [4a] {Ni8/Ni9W18}, [4b] {Ni12W35}, [4c] and {Ni20W34}, [4d] and the copper-containing derivatives {Cu14W36} [5a] and {Cu20W48X} (X=Cl, Br, I). [5b,c] Some transition-metal-containing polyoxomolybdates are also known, such as {Fe30Mo72}, [6a] {V30Mo72}, [6b] as well as {Co16Mo16} (two types of structures containing 16 cobalt centers, in the form of four tetramers). The class of cobalt-containing POMs was pioneered by Baker and Pope. Meanwhile a large number of POMbased Co complexes with nuclearities ranging from 2 to 16 has been reported. Our group has reported a nona-cobaltcontaining polyanion capped by six antenna-like Co ions in the solid state, as well as several polytungstates containing smaller numbers of cobalt ions. Very recently it was shown that [Co4(H2O)2(PW9O34)2] 10 [9a] is a hydrolytically and oxidatively stable homogeneous water-oxidation catalyst. During the past decade many high-nuclearity transitionmetal-based coordination complexes with interesting electronic and magnetic properties have been prepared. Some cobalt derivatives with nuclearities ranging from 2 to 32 are also known. It is a challenge to encapsulate high-nuclearity magnetic cores in diamagnetic POM shells, in particular by using conventional, soft synthesis methods. We have now succeeded in preparing the tetrameric 36-tungsto-8-phosphate [{Co4(OH)3PO4}4(PW9O34)4] 28 (1), containing 16 cobalt(II) centers (Figure 1).

Epoxidation of a range of alkenes with aqueous H 2 O 2 easily proceeds in the presence of the dititanium-containing 19-tungstodiarsenate(III) [Ti 2 (OH) 2 As 2 W 19 O 67 (H 2 O)] 8― (1), which contains five-coordinate Ti atoms. The results of product and kinetics studies support a mechanism that involves a reversible interaction between H 2 O 2 and the Ti―OH group of 1 to produce a titanium hydroperoxo complex followed by electrophilic oxygen atom transfer from the hydroperoxo ligand to the alkene substrate in the rate-limiting step. The effect of the alkene substrate nature has been investigated at the DFT level. A clear correlation between the energy of π C=C orbitals in the alkene and the turnover frequency values has been found, thereby indicating that the higher nucleophilicity of the alkene, the higher the reactivity. ONIOM (ONIOM = our own n-layered integrated molecular orbital and molecular mechanics) calculations have been employed to evaluate the role of steric effects of alkene substituents. The calculations show that the steric bulk can play a secondary role and tunes the activity in specific cases such as trans-stilbene.

The new polyoxometalate (IV) crystallizes in the monoclinic space group P21/n with Z = 4 (single crystal XRD).

The isomorphous compounds (IV) crystallize in the monoclinic space group C2/c with Z = 8 (single crystal XRD).

The area of lanthanide-containing polyoxometalates has been a field of large interest for several years due to the interesting structural and physicochemical properties of such compounds. This chemistry is dominated by tungsten based POMs, as a large number of vacant (lacunary) polytungstate precursors is known (as opposed to vanadium or molybdenum based POMs). The main subclasses in this field are lanthanide-containing iso- and hetero-polytungstates. The number of examples in the latter class is significantly larger than the former, probably because more lacunary hetero- than iso-polytungstates are known. Here we report on recent examples of lanthanide-containing iso- and hetero-polytungstates with a focus on synthetic and in particular structural aspects. The compounds discussed include discrete molecular species as well as 1-, 2- and 3-D solid-state assemblies.