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The first example of a discrete mixed platinum(iv)–gold(iii) oxoanion.

We report on the synthesis and structural characterizaton of the first example of a PdIV-containing polyoxopalladate(ii).

The synthesis of four organometallic RhCp*- and IrCp*-containing heteropoly-20-tungstates, [{RhCp*}2Bi2W20O70]10– (1), [{IrCp*}2Bi2W20O70]10– (2), [{RhCp*}2Sb2W20O70]10– (3), and [{IrCp*}2Sb2W20O70]10– (4) has been accomplished by reaction of (MCp*Cl2)2 with [X2W22O74(OH)2]12– in aqueous solution at pH 6 and 70 °C. The four polyanions 1–4 were structurally characterized in the solid state by single-crystal XRD, FTIR, and TGA and in solution by 183W and 13C NMR. For the Rh derivatives 1 and 3 the 183W–103Rh coupling (2JW-Rh 3.0 Hz) could be identified by 183W NMR.

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.

The 48‐FeIII‐containing 96‐tungsto‐16‐phosphate, [FeIII 48(OH)76(H2O)16(HP2W12O48)8]36− (Fe48), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {FeIII 6P2W12} units that are linked in an end‐on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe48 was synthesized by a simple one‐pot reaction of an {Fe22} coordination complex with the hexalacunary {P2W12} POM precursor in water. The title polyanion was characterized by single‐crystal XRD, FTIR, TGA, magnetic and electrochemical studies., A very large, discrete 96‐tungsto‐16‐phosphate containing 48 FeIII centers, [FeIII 48(OH)76(H2O)16(HP2W12O48)8]36− (Fe48), has been synthesized and structurally characterized. Polyanion Fe48 comprises eight equivalent {Fe6P2W12} units which are linked end‐on to form a macrocyclic assembly containing more iron centers than any other polyoxometalate known to date (see figure).

We report on the discovery of the first two examples of cationic palladium(II)-oxo clusters (POCs) containing f-metal ions, [Pd

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.

Here we report on the synthesis, structure, and characterization of the first example of a polyoxopalladate (POP)-based metal-organic framework (MOF). This novel class of materials comprises discrete polyoxo-13-palladate(II) nanocubes [Pd13O8(AsO4)8H6]8– decorated by four Ba2+ ions on each of two opposite faces. These secondary building units (SBUs) are linked to each other via rigid linear organic groups, resulting in a stable 3D POP-MOF framework, which exhibits interesting sorption as well as catalytic properties.

Despite their attractive properties, internal targeted alpha therapies using 223/224Ra are limited to bone-seeking applications. As there is no suitable chelator available, the search for new carriers to stably bind Ra2+ and to connect it to biological target molecules is necessary. Polyoxopalladates represent a class of compounds where Ra2+ can be easily introduced into the Pd-POM core during a facile one-pot preparation. Due to the formation of a protein corona, the connection to other targeting (bio)macromolecules is possible.

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.

In this study, the in vivo hypoglycemic effect of a donut-shaped polyanion salt (NH4)14[Na@P5W30O110]·31H2O {NaP5W30} and its Ag-containing derivative K14[Ag@P5W30O110]·22H2O·6KCl {AgP5W30}, as well as their hepatotoxicity and nephrotoxicity, was evaluated. In the screening hypoglycemic study, Wistar albino rats with streptozotocin induced diabetes were treated intraperitoneally with three single doses (5, 10, and 20 mg per kg per b.w.) of both investigated polyoxotungstates. The blood glucose levels, measured before and after 2, 4 and 6 h polyoxotungstate application, showed that both studied compounds induced the most pronounced and time dependent glucose lowering effects at the doses of 20 mg kg−1. Thus, daily doses of 20 mg kg−1 were administered to Wistar albino rats orally for 14 days in further toxicity examinations. The serum glucose concentration and biochemical parameters of kidney and liver function, as well as a histopathological analysis of kidney and liver tissues were evaluated 14 days after the polyoxotungstate administration. Both investigated compounds did not induce statistically significant alterations of the serum glucose and uric acid concentrations, as well as some of the liver function markers (serum alanine and aspartate aminotransferases, and alkaline phosphatase activities). However, the significant decrease in serum total protein and albumin concentrations and the increase in biochemical parameters of renal function – serum urea (up to 63.1%) and creatinine concentrations (up to 23.3%) were observed for both polyoxotungstates. In addition, the detected biochemical changes were in accordance with kidney and liver histhopathological analysis. Accordingly, the hepatotoxic and nephrotoxic effects of these potential antidiabetic polyoxotungstates could be considered as mild.

ConspectusNoble metal catalysts, in particular palladium-containing materials, are of prime commercial interest, because of their role as oxidation catalysts in automobile emission-control systems and reforming catalysts for the production of high-octane gasoline. However, despite almost two centuries of research, the precise structure of such materials is still ill-defined on the sub-nanometer scale, which severely limits the understanding of the underlying catalytic mechanisms. As a burgeoning class of structurally well-defined noble metal oxide nanoclusters, polyoxopalladates (POPs) have been highly rated as ideal models to fully decipher the molecular mechanism of noble metal-based catalysis. Being at the frontier of polyoxometalates (POMs), the chemistry of POPs, which are based exclusively on PdII centers as addenda is currently progressing rapidly, owing to their structural and compositional novelty, high solution stability, combined with promising applications especially as noble metal-based catal...

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.

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.

The cage-like cyclobutyltellurium(IV)-containing tungstoarsenate(III) dimers [(C4H8Te-OH)2(C4H8Te)6{As2W17O61(H2O)}2]14− (1) and [{(C4H8Te)2W2O5(H2O)2As2W19O67(H2O)}2]16− (2) were synthesized in moderately acidic aqueous medium by reaction of C4H8TeI2 with the lacunary tungstoarsenates(III) [B-α-AsW9O33]9− and [As2W19O67(H2O)]14−, respectively. Polyanion 1 was isolated as a mixed cesium-guanidinium salt Cs8.5(C(NH2)3)5.5[(C4H8TeOH)2(C4H8Te)6{As2W17O61(H2O)}2]·60H2O (1a), whereas 2 crystallized as a mixed cesium-potassium salt Cs9K7[{(C4H8Te)2W2O5(H2O)2As2W19O67(H2O)}2]·90H2O (2a). Single crystal X-ray analysis demonstrated that 1a and 2a crystallized in the triclinic space group $$ P \bar{1} $$ , with a = 12.7738(8) A, b = 18.7490(14) A, c = 21.9831(14) A, α = 111.155(4)o, β = 93.312(3)o, γ = 99.530(4) and Z = 1 for 1a and a = 19.309(6) A, b = 24.674(8) A, c = 26.071(8) A, α = 63.218(17)°, β = 89.26(16)°, γ = 79.948(17)° and Z = 2 for 2a. The polyanion salts 1a and 2a were characterized by solid state NMR (1H, 13C, 125Te), FT-IR, TGA-DSC, and elemental analysis.

(-)-Quinic acid possess eight possible stereoisomers, which occur both naturally and as products of thermal food processing. In this contribution, we have selectively synthesized four isomers, namely, epi-quinic acid, muco-quinic acid, cis-quinic acid, and scyllo-quinic acid, to develop a tandem LC-MS method identifying all stereoisomeric quinic acids. Four derivatives have been unambiguously characterized by single-crystal X-ray crystallography. The missing diastereomers of quinic acid were obtained by nonselective isomerization of (-)-quinic acid using acetic acid/concentrated H2SO4 allowing chromatographic separation and assignment of all diastereomers of quinic acid. We report for the first time that a full set of stereoisomers are reliably distinguishable on the basis of their tandem mass spectrometric fragment spectra as well as their elution order. A rationale for characteristic fragmentation mechanisms is proposed. In this study, we also observed that muco-quinic acid, scyllo-quinic acid, and epi-quinic acid are present in hydrolyzed Guatemalan roasted coffee sample as possible products of roasting.

The purpose of the study was to develop physically cross-linked novel pH-responsive gelatin – Wells–Dawson-type polyoxometalate (POM)-based self-assembled hydrogels using acrylic acid as a pH-responsive monomer. Cross-linking was achieved through electrostatic interactions between the cationic polymer and anionic Wells–Dawson POM [P2W15O56]12−. Ammonium persulfate and sodium hydrogen sulfite were used as initiators. The hydrogels were yellowish in color and exhibited low mechanical strength. Swelling, drug release, and pH sensitivity studies were conducted at pH 1.2 and 7.4. pH-dependent swelling and release of [P2W15O56]12− from the prepared hydrogels were observed, with a maximum at pH 7.4. The hydrogels were characterized by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy for evaluation of the surface morphology, hydrogel confirmation, and thermal properties. The results obtained confirmed the development o...

We report on the feasibility of applying high-resolution solid-state 195Pt MAS NMR spectroscopy for several PtIV-containing polyoxotungstates, and of 195Pt as well as 51V for a PtIV-containing polyoxovanadate. This method is particularly useful for polyanions which are unstable in solution and/or poorly soluble, as well as for systems exhibiting crystallographic disorder of Pt and W sites. We also report solution 195Pt and 183W NMR spectra of hexatungstoplatinate(IV) [H3PtW6O24]5− 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.

Three different Keggin-type polyoxometalates (POMs) [PW12O40]3−, [TiW11CoO40]7−, and [Ti2PW10O40]7−, were synthesized and then encapsulated in chitosan to prepare nanoparticles, CS–PW12, CS–TiW11Co, and CS–Ti2PW10. The synthesized nanoparticles were physicochemically characterized in terms of particle size, zeta potential, entrapment efficiency and in vitro release of the entrapped POM. The most efficient formulation was CS–TiW11Co, with a particle size of 105 ± 6 nm and an entrapment efficiency of 87 ± 12 (%). The CS–TiW11Co nanoparticles showed the highest activity when tested against tissue nonspecific alkaline phosphatase (TNAP) with IC50 = 102.0 ± 9.68 nM. The anticancer potential of the free POMs and their nanoparticles were also studied and CS–TiW11Co showed the highest inhibition (IC50 = 1.06 ± 0.09) on HeLa cells. To observe signs of apoptosis in HeLA cells, DAPI staining was performed after treatment with CS–TiW11Co nanoparticles. Furthermore, the reactive oxygen species (ROS) production was examined by H2DCF-DA dye under a fluorescence microscope. Our study revealed that CS–TiW11Co nanoparticles are very effective in cancer treatment and its associated metastasis especially in osteoblastic lesions with minimal adverse effects on normal cells (Vero cells).

The development of rational synthetic procedures with desired nuclearity and high selectivity is a critical issue in inorganic chemistry. Here we demonstrate a comprehensive understanding of the template effect induced by metal cations in the formation mechanism of the class of polyoxopalladates ({MPd12L8} nanocube and {MPd15L10} nanostar) by combining computational and experimental techniques. The capture of a Mn+ guest ion by a peripheral palladium(II)-oxo shell leads to a competition between the parent Pd2+ addenda ion and the respective guest metal ion. The present study reveals that (i) the selection of the incorporated guest ion has a thermodynamic control, (ii) the main factors governing the formation of a particular polyanion are the charge and size of the guest cation, (iii) the electrostatic interaction between the cation and the surrounding oxo ligands and (iv) the dehydration ability of the cation. As expected from the number of observed {Mn+Pd12L8} species, trivalent cations M3+ were found to be good templates resulting in several examples of {M3+Pd12L8}, whereas monovalent cations M+ are much less prone to form {M+Pd12L8}. For tetravalent cations the dehydration energies are very large, however, the formation of {M4+Pd12L8} nanocubes is found to be still energetic favourable. Fully consistent with computational predictions, four novel polyoxo-12-palladates were synthesized: the La3+-centered nanocube [LaPd12O8(PhAsO3)8]5− (LaPd12-closed), the La3+-centered “open” nanocube [LaPd12O6(OH)3(PhAsO3)6(OAc)3]3− (LaPd12-open), the Ga3+-centered [GaPd12O8(PhAsO3)8]5− (GaPd12), and the In3+-analogue [InPd12O8(PhAsO3)8]5− (InPd12). All four compounds were fully characterized in the solid state and in solution by a multitude of physicochemical techniques, including 71Ga and 115In NMR as well as mass spectrometry. The experimentally observed selective incorporation of only In3+ ions in the presence of Ga3+ and In3+ confirmed the thermodynamic control of the formation mechanism, which we had predicted by theory.

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.

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The oxalato-titanium(IV)-containing, dimeric 18-tungsto-2-phosphate [Ti8(C2O4)8P2W18O76(H2O)4]18− (1) and the 32-tungsto-4-phosphate [Ti6(C2O4)4P4W32O124]20− (2) are formed upon reaction of the oxalato-titanium complex [TiO(C2O4)2]2− with the trilacunary Keggin precursor [A-α-PW9O34]9− and the hexalacunary Wells–Dawson precursor [H2P2W12O48]12−, respectively. Polyanion 1 consists of two {PW9} units encapsulating eight titanium centers and connected to each other via two Ti–O–Ti bridges, and crystallizes as a mixed potassium-sodium-lithium salt in the triclinic space group $$P{\bar{1}}$$ . Polyanion 2 comprises two {P2W16} units containing each two titanium atoms, and the two half-units are connected via two titanium atoms decorated by two oxalate groups each, and crystallizes as a mixed potassium-lithium salt in the rhombohedral space group $$R{\bar{3}}c$$ . Polyanions 1 and 2 were characterized in the solid state by single-crystal XRD, FT-IR, and TGA, whereas polyanion 2 was also investigated by 31P and 183W NMR.

We report on an improved synthesis and structural characterization of the cyclic 48-tungsto–8-arsenate(V) [H4As8W48O184]36− (1). The mixed lithium–potassium salt of this polyanion, K26.5Li9.5[H4As8W48O184]·90H2O (KLi-1), has been studied in the solid state by IR, single-crystal X-ray diffraction, and elemental analysis, and in solution by 183W NMR spectroscopy.

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 A. 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.

The hepta-Ni(2+)-containing 30-tungsto-4-phosphate(v) [Ni7(OH)6(H2O)6(P2W15O56)2](16-) (1) has been synthesized in aqueous, slightly basic medium under conventional reaction conditions, and charactarized via different physical methods. Single-crystal XRD showed that 1 consists of a corner-fused double-cubane {Ni7(OH)6(H2O)6}(8+) fragment sandwiched by two trilacunary [P2W15O56](12-) units. Polyanion 1 is solution-stable as shown by (31)P NMR. Ferromagnetic coupling interaction between the 7 paramagnetic centers of the double-cubane core in 1 with a S = 7 ground state was demonstrated. Electrochemical studies were also performed on 1.

The synthetic macrocycle cucurbit[6]uril forms host-guest inclusion complexes with molecular dibromine and diiodine. As evidenced by their crystal structures, the encapsulated dihalogens adapt a tilted axial geometry and are held in place by two different types of halogen-bonding interactions, one with a water molecule (bond distances 2.83 Å for O···Br and 3.10 Å for O···I) and the other one with the ureido carbonyl groups of the molecular container itself (bond distances 3.33 Å for O···Br and 3.49 Å for O···I). While the former is of the conventional type, involving the lone electron pair of an oxygen donor, the latter is perpendicular, involving the π-system of the carbonyl oxygen (N-C═O···X dihedrals ca. 90°). Such perpendicular interactions resemble those observed in protein complexes of halogenated ligands. A statistical analysis of small-molecule crystal structural data, as well as quantum-chemical calculations with urea as a model (MP2/aug-cc-pVDZ-PP), demonstrates that halogen bonding with the π-system of the carbonyl oxygen can become competitive with the commonly favored lone-pair interaction whenever the carbonyl group carries electron-donating substitutents, specifically for ureas, amides, and esters, and particularly when the lone pairs are engaged in orthogonal hydrogen bonding (hX bonds). The calculations further demonstrate that the perpendicular interactions remain significantly attractive also for nonlinear distortions of the O···X-X angle to ca. 140°, the angle observed in the two reported crystal structures. The structural and theoretical data jointly support the assignment of the observed dihalogen-carbonyl contacts as genuine halogen bonds.

Reaction of (C2H5)2SnCl2 with the trilacunary 9-tungstoarsenate(V) [A–α–AsW9O34]9− in aqueous pH 5 medium resulted in the diethyltin-containing polyanion [{Sn(C2H5)2}3(H2O)6(A–α–AsVW9O34)]3− (1), which crystallized as a hydrated guanidinium salt, [C(NH2)3]3[{Sn(C2H5)2}3(H2O)4(A–α–AsVW9O34)]·9H2O (1a). Polyanion 1 represents the first example of a diethyltin-containing polyanion. The diethyltin groups are bound to the trilacunary Keggin units via two Sn–O(W) bonds involving edge-shared WO6 octahedra. Each Sn atom also has two terminal, cis-related water ligands, and two terminal, trans-related ethyl groups. Multinuclear (1H, 13C, 119Sn, 183W) NMR spectrometry indicated that polyanion 1 is stable in solution. Compound 1a was structurally characterized in the solid state by single-crystal XRD, FT-IR, as well as thermogravimetric and elemental analyses. Single-crystal X-ray analysis showed that 1a crystallizes in the orthorhombic system, space group P nma , with a = 23.5280(10) A, b = 15.5435(6) A, c = 18.6191(9) A, V = 6809.1(5) A3 and Z = 4. The structure of 1a is an extended 2D assembly of individual polyanion units 1 linked via Sn–O(W) bridges.

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.

The trimeric, cyclic polyanion [(α-Ti3GeW9O37OH)3(TiO3(OH2)3)]17− (Ti10) was synthesized by reaction of [A-α-GeW9O34]10− with K8[Ti4O4(C2O4)8] in a mixture of rubidium and lithium acetate buffers at 60 °C, and then crystallized as a mixed rubidium-potassium-sodium salt, Rb13K2Na2[(α-Ti3GeW9O37OH)3(TiO3(OH2)3)]·40H2O (Rb-Ti10). The title compound was characterized in the solid state by IR, single-crystal XRD, TGA and elemental analysis, and in solution by 183W-NMR. In order to prepare a pure sample of Rb-Ti10, several reaction parameters need to be carefully controlled, such as the ratio of rubidium and lithium acetate buffers, the choice of titanium precursor (K8[Ti4O4(C2O4)8]), the reaction temperature, and very importantly, the concentration of rubidium ions.

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).

Visible or sunlight irradiation of high nuclearity cobalt-or nickel-centers containing polyoxometalates (POMs), alone or in association with colloidal TiO2, results in their neat, apparently direct, multielectron reduction. These materials prove very effective in the first example of visible or sunlight driven POM-based degradation of Acid Orange 7.

The catalytic properties of the sandwich polyoxometalate [Ti2(OH)2As2W19O67(H2O)]8−, which contains two (B-α-AsIIIW9O33) fragments linked together by a “belt” consisting of one octahedral WO(H2O)4+ and two square-pyramidal Ti(OH)3+ groups, have been investigated in the selective liquid-phase oxidation of organic compounds by aqueous hydrogen peroxide. The polyoxometalate shows high catalytic activity and selectivity in the oxidation of alkenes, alcohols, diols, and thioethers. The composition of the reaction products indicates that hydrogen peroxide is activated via a heterolytic mechanism.

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 oxidation of alkenes by H(2)O(2) catalyzed by Ti(IV)-containing polyoxometalates (POMs) as models of Ti single-site catalysts has been investigated at DFT level and has been compared with other early transition-metal-substituted polyoxometalates. We have studied in detail the reaction mechanism of the C(2)H(4) epoxidation with H(2)O(2) mediated by two different POMs, the Ti-monosubstituted Keggin-type POM [PTi(OH)W(11)O(39)](4-) and the Ti-disubstituted sandwich-type POM [Ti(2)(OH)(2)As(2)W(19)O(67)(H(2)O)](8-). These species exhibit well-defined 6- and 5-coordinated titanium environments. For both species, the reaction proceeds through a two-step mechanism: (i) the Ti-OH groups activate H(2)O(2) with a moderate energy barrier yielding either Ti-hydroperoxo (Ti(IV)-OOH) or Ti-peroxo (Ti(IV)-OO) intermediate, and (ii) the less stable but more reactive Ti-hydroperoxo species transfers oxygen to alkene to form the epoxide, this latter step being the rate-determining step. The higher activity of the sandwich anion was attributed to the absence of dimer formation, and its higher selectivity to the larger energy cost of homolytic O-O bond breaking in the hydroperoxo intermediate. We also propose several requisites to improve the efficiency of Ti-containing catalysts, including flexible and 5-fold (or lower) coordinated Ti environments, as well as reagent-accessible Ti sites. Calculations on other TM-containing Keggin-type POMs [PTM(OH)W(11)O(39)](4-) (TM = Zr(IV), V(V), Nb(V), Mo(VI), W(VI), and Re(VII)) showed that when we move from the left to the right in the periodic table the formation of the epoxide via peroxo intermediate becomes competitive because of the higher mixing between the orbitals of the TM and the O-O unit.

The 20-tungsto-4-tellurate(IV) polyanion [H2Te4W20O80]22− (1) has been synthesized and isolated in the form of its hydrated sodium salt Na22[H2Te4W20O80]·64H2O (Na-1). Na-1 has been characterized in the solid state by FTIR and TGA. Single-crystal X-ray diffraction analysis revealed that Na-1 crystallizes in the triclinic space group P $${\bar 1}$$ , with a = 12.741(2) A, b = 16.842(3) A, c = 17.197(4) A, α = 93.961(10)°, β = 107.466(8)°, γ = 108.548(8)°, V = 3281.5(11) A3 and Z = 1. The polyanion 1 comprises two [HTe2W10O40]11− fragments, connected through Te−O–W μ2-oxo bridges, and each containing a pair of face-shared WO6 octahedra. Furthermore, the 15-tungstotellurate(IV) polyanion [NaTeW15O54]13− (2) was synthesized and crystallized as a sodium salt in the orthorhombic space group Pccn, with a = 11.8841(5) A, b = 20.8934(11) A, c = 31.801(2) A, V = 7896.3(7) A3 and Z = 4.

(Chemical Equation Presented) Not like the others: A molecular palladium oxide cluster was formed by self-assembly of palladium(II) and arsenic(V) using mild reaction conditions. The resulting heteropolypalladate [Pd II 13AsV 8O34(OH) 6]8- has a distorted cubic shape and edge lengths of about 1 nm. The thirteen PdII ions retain four-coordinate square-planar geometry, in marked contrast to all other known discrete polyoxometalates.

The mixed-valence 24-vanadophosphate \( {\left[ {{\left\{ {{\text{Ru}}^{{{\text{II}}}}_{3} (dmso)_{9} {\text{PV}}^{{\text{V}}}_{{11}} {\text{V}}^{{{\text{IV}}}} {\text{Ru}}^{{{\text{III}}}} {\text{O}}_{{37}} {\text{(OH)}}_{3} } \right\}}_{2} } \right]}^{{8 - }} \) (1) has been synthesized and characterized in the solid state by IR, magnetism, EPR, XPS, and elemental analysis. Single-crystal X-ray analysis was carried out on \( {\text{Na}}_{8} {\left[ {{\left\{ {{\text{Ru}}^{{{\text{II}}}}_{3} (dmso)_{9} {\text{PV}}^{{\text{V}}}_{{11}} {\text{V}}^{{{\text{IV}}}} {\text{Ru}}^{{{\text{III}}}} {\text{O}}_{{37}} {\text{(OH)}}_{3} } \right\}}_{2} } \right]} \cdot 46{\text{H}}_{2} {\text{O}} \) (Na-1), which crystallizes in the triclinic system, space group \( \hbox{P}\overline{1} \), with a = 17.168(3) A, b = 18.1971(14) A, c = 20.1422(13) A, α = 114.753(3)°, β = 99.390(4)°, γ = 95.124(4)°, and Z = 2. Polyanion 1 has an unusual, open structure composed of 2 RuIIIO6 octahedra, 2 VIVO6 octahedra, 14 VVO5 square-pyramids, 8 VVO4 tetrahedra, and 2 PO4 tetrahedra which are all directly linked via edges and corners. The outer surface of 1 is decorated with six RuII(dmso)3 groups. XPS studies on Na-1 confirm the presence of 2 RuIII and 6 RuII as well as 22 VV and 2 VIV centers. Magnetic susceptibility data on Na-1 show that the VIV–RuIII pairs are coupled antiferromagnetically, with J1 = −13 K and J2 ∼ −3 K. We did not detect any peak in our EPR measurements on Na-1, thus supporting the conclusion that Na-1 is diamagnetic in its ground state.