Crystal-to-crystal polymerisation of monosubstituted [PW11O39Cu(H2O)]5- Keggin-type anions.

The reaction between neutral bis(picolinate)copper(II) complexes and copper(II)-monosubstituted Keggin-type phosphotungstate anions formed in situ leads to the formation of the hybrid [C(NH2)3]10[{PW11O39Cu(H2O)}2{Cu(pic)2}]·10H2O compound (1, pic = picolinate) in the presence of structure-directing guanidinium cations. Single-crystal X-ray diffraction studies demonstrate that 1 contains dimeric {PW11O39Cu(H2O)}2{Cu(pic)2} molecular species constituted by two Keggin-type anions linked by one {Cu(pic)2} octahedral complex through axial coordination to their terminal oxygen atoms. The extensive hydrogen-bonding network established by guanidium cations and Keggin clusters plays a key role in retaining the crystallinity of the system throughout dehydration to allow a single-crystal-to-single-crystal (SCSC) transformation into the anhydrous [C(NH2)3]10[{PW11O39Cu}2{Cu(pic)2}] (2a) at 170 °C. Structural modifications involve the re-orientation, shifting in ca. 1.5 Å and condensation of all the {PW11O39Cu} units to result in {PW11O39Cu}n chains in an unprecedented solid-state polymerisation. This phase transition also implies the cleavage of Cu-O bonds induced by the rotation and translation of Keggin-type anions, in such a way that hybrid dimeric units in 1 are dismantled and {Cu(pic)2} complexes become square planar. The irreversibility of the phase transition has been confirmed by combined thermal and diffractometric analyses, which evidence that the anhydrous phase adsorbs only one water molecule per cluster to become the [C(NH2)3]10[{PW11O39Cu}2{Cu(pic)2}]·2H2O (2h) hydrated derivative without any significant alteration in its cell parameters, nor in its crystalline structure. Phase transformations have been monitored by electron paramagnetic resonance spectroscopy.

Determination of hazardous vapors from the thermal decomposition of organochlorinated silica xerogels with adsorptive properties.

The incorporation of organic groups into sol-gel silica materials is known to have a noticeable impact on the properties and structure of the resulting xerogels due to the combination of the properties inherent to the organic fragments (functionality and flexibility) with the mechanical and structural stability of the inorganic matrix. However, the reduction of the inorganic content in the materials could be detrimental to their thermal stability properties, limiting the range of their potential applications. Therefore, this work aims to evaluate the thermal stability of hybrid inorganic-organic silica xerogels prepared from mixtures of tetraethoxysilane and organochlorinated triethoxysilane precursors. To this end, a series of four materials with a molar percentage of organochlorinated precursor fixed at 10%, but differing in the type of organic group (chloroalkyls varying in the alkyl-chain length and chlorophenyl), has been selected as model case study. The gases and vapors released during the thermal decomposition of the samples under N2 atmosphere have been analyzed and their components determined and quantified using a thermogravimetric analyzer coupled to a Fourier-transform infrared spectrophotometer and to a gas chromatography-mass spectrometry unit. These analyses have allowed to identify up to three different thermal events for the pyrolysis of the organochlorinated xerogel materials and to elucidate the reaction pathways associated with such processes. These mechanisms have been found to be strongly dependent on the specific nature of the organic group.

Gold Nanoparticles Capped with a Novel Titanium(IV)-Containing Polyoxomolybdate Cluster: Selective and Enhanced Bactericidal Effect Against Escherichia coli.

Bacterial infections are a public health threat of increasing concern in medical care systems; hence, the search for novel strategies to lower the use of antibiotics and their harmful effects becomes imperative. Herein, the antimicrobial performance of four polyoxometalate (POM)-stabilized gold nanoparticles (Au@POM) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as Gram-negative and Gram-positive bacteria models, respectively, is studied. The bactericidal studies performed, both in planktonic and sessile forms, evidence the antimicrobial potential of these hybrid nanostructures with selectivity toward Gram-negative species. In particular, the Au@GeMoTi composite with the novel [Ti2 (HGeMo7 O28 )2 ]10- POM capping ligand exhibits outstanding bactericidal efficiency with a minimum inhibitory concentration of just 3.12 µm for the E. coli strain, thus outperforming the other three Au@POM counterparts. GeMoTi represents the fourth example of a water-soluble TiIV -containing polyoxomolybdate, and among them, the first sandwich-type structure having heteroatoms in high-oxidation state. The evaluation of the bactericidal mechanisms of action points to the cell membrane hyperpolarization, disruption, and subsequent nucleotide leakage and the low cytotoxicity exerted on five different cell lines at antimicrobial doses demonstrates the antibiotic-like character. These studies highlight the successful design and development of a new POM-based nanomaterial able to eradicate Gram-negative bacteria without damaging mammalian cells.

Consecutive Single-Crystal-to-Single-Crystal Isomerization of Novel Octamolybdate Anions within a Microporous Hybrid Framework with Robust Water Sorption Properties.

The 3D hybrid framework [{Cu(cyclam)}3 (κ-Mo8 O27 )] ⋅ 14H2 O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-single-crystal transformations upon heating to afford two different anhydrous phases (2 a and 3 a). These transitions modify the framework dimensionality and enable the isomerization of κ-octamolybdate (κ-Mo8 ) anions into λ (2 a) and µ (3 a) forms through metal migration. Hydration of 3 a involves condensation of one water molecule to the cluster to afford the γ-Mo8 isomer in 4, which dehydrates back into 3 a through the 6 a intermediate. In contrast, 2 a reversibly hydrates to form 5, exhibiting the same Mo8 cluster as that of 1. It is remarkable that three of the Mo8 clusters (κ, λ and µ) are new and that up to three different microporous phases can be isolated from 1 (2 a, 3 a, and 6 a). Water vapor sorption analyses show high recyclability and the highest uptake values for POM-based systems. The isotherms display an abrupt step at low humidity level desirable for humidity control devices or water harvesting in drylands.

Manejo de Disminución de Movimientos Fetales en pacientes del Área de Urgencias Obstétricas / Management of Decreased Fetal Movements in patients in the Obstetric Emergency Area

Los movimientos fetales son uno de los primeros signos de vitalidad fetal. Durante la gestación, éstos van apareciendo progresivamente. La adecuada adquisición y mantenimiento de los mismos durante la gestación indica un correcto desarrollo neuromuscular, así como de bienestar fetal1. La percepción materna de una Disminución de los Movimientos Fetales (DMF) constituye un motivo de consulta frecuente en los Servicios de Urgencias Obstétricas; toda paciente embarazada debe vigilar los movimientos fetales, mediante un conteo subjetivo de los movimientos del feto, a partir de las 24 semanas de gestación. La DMF constituye el 5 ­ 15% de motivos de consulta en los servicios de Urgencias en el tercer trimestre del embarazo. Hasta un 25% de fetos que presentan una DMF presentarán alguna complicación perinatal (malformaciones, retraso de crecimiento, parto prematuro, hemorragia fetomaterna, y éxitus fetal) incluso en población de bajo riesgo. El manejo inadecuado de la DMF representa un 10-15% de las muertes evitables a término1-3. Es por esto que ninguna paciente que consulte por Disminución de Movimientos Fetales debe ser dada de alta sin asegurarse del adecuado bienestar fetal.

Fetal movements are one of the first signs of fetal vitality. During gestation, they appear progressively. Adequate acquisition and maintenance of fetal movements during gestation indicates correct neuromuscular development, as well as fetal well-being1. Maternal perception of decreased fetal movements (DMP) is a frequent reason for consultation in Obstetric Emergency Departments; every pregnant patient should monitor fetal movements by subjectively counting fetal movements, starting at 24 weeks of gestation. FMD constitutes 5-15% of the reasons for consultation in the emergency department in the third trimester of pregnancy. Up to 25% of fetuses with FMD will present some perinatal complication (malformations, growth retardation, premature delivery, fetomaternal hemorrhage, and fetal death) even in low-risk populations. Inadequate management of FMD accounts for 10-15% of preventable deaths at term1-3. This is why no patient who consults for decreased fetal movements should be discharged without ensuring adequate fetal well-being.

Isolation of the Elusive Heptavanadate Anion with Trisalkoxide Ligands.

The unprecedented heptavanadate cluster has been isolated from reactions between trisalkoxide ligands and vanadate in water at pH = 2 as a series of alkylammonium [HxV7O18(H2O)((OCH2)3CR)](4-x)- salts (1-3, R = CH2OH; 4, R = CH3). Their structures have been determined and the partial stability of 4 in water assessed by a combination of multinuclear NMR spectroscopy and ESI-MS. The heptavanadate unit reported herein could represent an intermediate species in the formation of decavanadate that is blocked by attachment of tripodal ligands.

In Situ Synthesis of SERS-Active Au@POM Nanostructures in a Microfluidic Device for Real-Time Detection of Water Pollutants.

We present a simple, versatile, and low-cost approach for the preparation of surface-enhanced Raman spectroscopy (SERS)-active regions within a microfluidic channel 50 cm in length. The approach involves the UV-light-driven formation of polyoxometalate-decorated gold nanostructures, Au@POM (POM: H3PW12O40 (PW) and H3PMo12O40 (PMo)), that self-assemble in situ on the surface of the polydimethylsiloxane (PDMS) microchannels without any extra functionalization procedure. The fabricated LoCs were characterized by scanning electron microscopy (SEM), UV-vis, Raman, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The SERS activity of the resulting Au@POM-coated lab-on-a-chip (LoC) devices was evaluated in both static and flow conditions using rhodamine R6G. The SERS response of Au@PW-based LoCs was found to be superior to Au@PMo counterparts and outstanding when compared to reported data on metal@POM nanocomposites. We demonstrate the potentialities of both Au@POM-coated LoCs as analytical platforms for real-time detection of the organophosphorous pesticide paraoxon-methyl at 10-6 M concentration level.

The effect of the orientation of the Jahn-Teller distortion on the magnetic interactions of trinuclear mixed-valence Mn(ii)/Mn(iii) complexes.

Two new trinuclear manganese complexes, [Mn3(L1)(µ-OCH3)2(N3)2]·CH3OH (1) and [Mn3(L2)(µ-OCH3)2(N3)2]·CH3OH (2), have been obtained from the reaction of Mn(OAc)2 4H2O, NaN3 and the preformed N6O4-donor H4L1 or H4L2 compartmental ligands, which are synthesized via Schiff base condensation of pentaethylenehexamine with 2-hydroxybenzaldehyde or 2-hydroxy-3-methoxybenzaldehye, respectively. Complexes 1 and 2 have been characterized by spectroscopic methods and single-crystal X-ray analysis. The structural studies indicate that both 1 and 2 are mixed-valence complexes containing angular Mn(iii)-Mn(ii)-Mn(iii) cores in which the metal centers are connected to each other by phenoxido and methoxido bridging groups. The coordination environment around the manganese ions is analogous in both complexes, but for a change in the direction of the Jahn-Teller distortion around the external Mn(iii) ions when going from 1 to 2, which is mainly attributed to the steric effect of different substituents on the phenyl rings of the ligands. The analysis of the magnetic susceptibility data indicates the presence of antiferromagnetic intramolecular coupling in both complexes, but the interaction in 1 was found to be nearly one order of magnitude weaker than that in 2. This fact is rationalized on the basis of the different orientation of the Jahn-Teller distortion, which modifies the magnetic exchange pathway through the phenoxido bridges from the equatorial-axial connection type observed in 1 to the axial-axial linkages displayed by 2.

Thermostructural Behavior in a Series of Lanthanide-Containing Polyoxotungstate Hybrids with Copper(II) Complexes of the Tetraazamacrocycle Cyclam: A Single-Crystal-to-Single-Crystal Transformation Study.

A series of 14 isostructural [Cu(cyclam)]2[{Cu(cyclam)}4{(α-GeW11O39)Ln(H2O)(OAc)}2]·18H2O (1-Ln, where Ln = La-Lu; cyclam = 1,4,8,11-tetraazacyclotetradecane) polyoxometalate-based hybrids reported herein represent (i) the first example of a two-dimensional covalent hybrid lattice involving the [{(α-XW11O39)Ln(H2O)(OAc)}2] n- archetype and (ii) the first structural characterization of such a dimeric polyoxotungste for Ln = La and Pr as well as for the combination of X = Ge and Ln = Ce, Nd, Sm, or Lu. Compounds 1-Ln have been characterized by elemental analyses, infrared spectroscopy, and thermogravimetric analysis, and their thermostructural behavior has been monitored by powder and single-crystal X-ray diffraction. The title compounds undergo two single-crystal-to-single-crystal transformations triggered by thermal dehydration leading to the [{Cu(cyclam)}6{(α-GeW11O39)Ln(H2O)(OAc)}2]·4H2O intermediate (2-Ln, where Ln = Eu or Er) and [Cu(cyclam)]0.5[{Cu(cyclam)}5.5{(α-GeW11O39)Ln(OAc)}2] (3-Ln, where Ln = Ce or Eu) final anhydrous phases, the latter evidencing a coordinatively unsaturated derivative of the dimeric archetype for the first time. These transitions involve formation and disruption of Cu-OPOM bonds that result in different {Cu(cyclam)}2+ moieties grafting onto and being released from Keggin surfaces, which reduces the dimensionality of 1-Ln to one-dimensional covalent assemblies for 2-Ln and 3-Ln. While all 3-Ln phases rehydrate fully upon exposure to air for 24 h, the kinetics governing the crystal transitions back toward 1-Ln through 2-Ln depend on the nature of Ln. Under ambient moisture, the anhydrous structures fully revert back to the parent framework for Ln = La-Sm, while the samples containing Eu to Lu afford mixtures of 1-Ln and 2-Ln and require immersion in water for the structural reversion to reach completion. Single-crystal X-ray diffraction analyses of the rehydrated 1R-Ln samples (Ln = Ce, Eu, and Er) support these observations.

Single-crystal-to-single-crystal transformations triggered by dehydration in polyoxometalate-based compounds.

Single-crystal-to-single-crystal transformations are solid-state phase transitions between different crystalline states in which the crystal integrity and the long-range structural order are retained through the whole transformation process. Such a phenomenon constitutes the structural response that some compounds afford when being exposed to a given external stimulus (temperature, pressure, light, etc.) and, therefore, its study has become a relevant focus of interest within crystal engineering because it allows for monitoring how certain properties (colour, magnetism, luminescence, porosity) of the stimuli-responsive material are modified as the structure evolves into the activated form. A range of organic, inorganic and hybrid systems have been found to undergo such phase transitions, but these examples only include a small number of compounds that incorporate polyoxometalate anions, among which the removal of guest solvent molecules (dehydration) stands out as the most common external stimulus able to induce the occurrence of a single-crystal-to-single-crystal transformation. This feature article compiles the examples of dehydration-triggered single-crystal-to-single-crystal transformation studies that have been reported to date for polyoxometalate-based compounds and reviews some of their most relevant structural aspects.

Zirconia-supported 11-molybdovanadophosphoric acid catalysts: effect of the preparation method on their catalytic activity and selectivity.

The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle.

Immobilization of Polyoxometalates on Tailored Polymeric Surfaces.

Herein we describe the preparation of hybrid polymer-inorganic interfaces by the immobilization of polyoxometalate nanoclusters on functionalized polymer surfaces. The polymeric surfaces were made of polystyrene-b-poly(acrylic acid)/polystyrene (PS-b-PAA/PS) blends by spin coating on a silicon wafer. The functionalization of the polymer film was obtained by interfacial migration of the amphiphilic block copolymer toward the interface upon water vapor annealing. The carboxylic acid functional groups contained in the PAA block were then employed to anchor the [LnIII(α-SiW11O39)]5- polyoxometalates (Ln: Ce, Er). This purpose was achieved by immersing the films in aqueous solutions of the in situ-formed inorganic nanoclusters. X-ray photoelectron and confocal Raman spectroscopies, together with atomic force microscopy, confirmed the immobilization of the inorganic species at the interface.

Thermally-Triggered Crystal Dynamics and Permanent Porosity in the First Heptatungstate-Metalorganic Three-Dimensional Hybrid Framework.

The hybrid compound [{Cu(cyclam)}3 (W7 O24 )]⋅15.5 H2 O (1) (cyclam=1,4,8,11-tetraaza-cyclotetradecane) was synthesized by reacting the {Cu(cyclam)}2+ complex with a tungstate source in water at pH 8. Compound 1 exhibits an unprecedented three-dimensional covalent structure built of heptatungstate clusters linked through metalorganic complexes in a POMOF-like framework that displays water-filled channels. This dynamic architecture undergoes two sequential single-crystal-to-single-crystal transformations upon thermal evacuation of water molecules to result in the partially dehydrated [{Cu(cyclam)}3 (W7 O24 )]⋅12 H2 O (2) and anhydrous [Cu(cyclam)]0.5 [{Cu(cyclam)}2.5 (W7 O24 )] (3) crystalline phases. These transitions are associated with cluster rotations and modifications in the CuII coordination geometries, which reduce the dimensionality of the original lattice to layered systems but preserving the porous nature. Phase 3 reverts to 2 upon exposure to ambient moisture, whereas the transition between 1 and 2 proved to be irreversible. The permanent microporosity of 3 was confirmed by gas sorption measurements (N2 , CO2 ), which reveal a system of parallel channels made of wide cavities connected through narrow necks that limit the adsorption process. This observation is in good agreement with Grand Canonical Monte Carlo simulations.

A Simple Approach To Develop Tailored Mesoporosity in Nanostructured Heteropolysalts.

In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin-type [PMo12 O40 ]3- heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro- and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts.

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes.

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1, cyclam = 1,4,8,11-tetraazacyclotetradecane) was prepared by reaction of (VO3)(-) anions and {Cu(cyclam)}(2+) complexes in NaCl (aq) at pH 4.6-4.7 and characterized by elemental analyses, thermogravimetry, and X-ray diffraction (powder, single-crystal) techniques. Compound 1 exhibits a POMOF-like supramolecular open-framework built of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross sections of 10.4 × 8.8 Å(2). The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.

New Perspectives for Old Clusters: Anderson-Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d-4 f Species.

A series of nine [Sb7W36O133Ln3M2(OAc)(H2O)8](17-) heterometallic anions (Ln3M2; Ln=La-Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs-type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW9O33} capping unit formed by a planar {MW6O24} fragment to which three {WO2} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ɛ-Keggin cluster. It is shown, for the first time, that classical Anderson-Evans {MW6O24} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk-shaped species is also revealed. The Ln3M2 anions possess chirality owing to a {Sb4O4} cluster being encapsulated in left- or right-handed orientations. Their ability to self-associate in blackberry-type vesicles in solution has been assessed for the Ce3Co2 derivative.

Crown-shaped tungstogermanates as solvent-controlled dual systems in the formation of vesicle-like assemblies.

Reaction of early lanthanides, GeO2 , and Na2 WO4 in a NaOAc buffer results in large crown-shaped polyoxometalates based on [Ln2 GeW10 O38 ](6-) subunits. By using Ni(2+) as a crystallizing agent, [Na⊂Ln12 Ge6 W60 O228 (H2 O)24 ](35-) (Na⊂Ln12 ) hexamers formed by alternating ß(1,5)/ß(1,8) subunits were obtained for Ln=Pr, Nd. The addition of K(+) led to a similar anion for Ln=Sm, namely, [K⊂Sm12 Ge6 W60 O228 (H2 O)22 ](35-) (K⊂Sm12 ) and [K⊂K7 Ln24 Ge12 W120 O444 (OH)12 (H2 O)64 ](52-) (K⊂Ln24 ) dodecamers that consist of a central core identical to K⊂Sm12 decorated with six external γ(3,4) subunits for Ln=Pr, Nd. These anions dissociate in water into hexameric cores and monomeric entities, as shown by ESI mass spectrometry. The former self-assemble into spherical, hollow, and single-layered blackberry-type structures with radii of approximately 75 nm, as monitored by laser light scattering (LLS) and TEM techniques. Analogous studies performed for K⊂Nd24 in water/acetone mixtures show that the dodecamers remain stable and form in turn their own type of blackberries with sizes that increase from approximately 20 to 50 nm with increasing acetone content. This control over both the composition and size of the vesicle-like assemblies is achieved for the first time by modifying the architecture of the species that undergoes supramolecular association through the solvent polarity.

Rearrangement of a Krebs-type polyoxometalate upon coordination of N,O-bis(bidentate) ligands.

Selective coordination of 2,3-pyzdc to the Krebs-type [{Ni(H2O)3}2(WO2)2(SbW9O33)2](10-) anion promotes a skeletal rearrangement that results in the [(2,3-pyzdc)2{NaNi2(H2O)4Sb2W20O70}2](22-) (Ni4) hybrid dimer showing a novel dinickel containing a 20-tungsto-2-antimonate(III) framework stabilized by N,O-bis(bidentate) bridging ligands. The solution stability and magnetism of Ni4 is discussed.

Functionalization of Krebs-type polyoxometalates with N,O-chelating ligands: a systematic study.

The first organic derivatives of 3d-metal-disubstituted Krebs-type polyoxometalates have been synthesized under mild bench conditions via straightforward replacement of labile aqua ligands with N,O-chelating planar anions on either preformed or in situ-generated precursors. Nine hybrid clusters containing carboxylate derivatives of five- or six-membered aromatic N-heterocycles as antenna ligands have been obtained as pure crystalline phases and characterized by elemental and thermal analyses, infrared spectroscopy, and single-crystal X-ray diffraction. They all show the general formula [{M(II)L(H2O)}2(WO2)2(B-ß-XW9O33)2](n-) and can be classified as follows: 1-SbM, where L = 1H-imidazole-4-carboxylate (imc), X = Sb(III), n = 12, and M(II) = Mn, Co, Ni, Zn; 1-TeM, where L = imc, X = Te(IV), n = 10, and M(II) = Mn, Co; 2-SbNi, where L = 1H-pyrazole-3-carboxylate (pzc), X = Sb(III), n = 12, and M(II) = Ni; and 3-SbM, where L = pyrazine-2-carboxylate (pyzc), X =Sb(III), n = 12, and M(II) = Co, Zn. The 3d-metal-disubstituted tungstotellurate(IV) skeleton of compounds 1-TeM is unprecedented in polyoxometalate chemistry. The stability of these hybrid Krebs-type species in aqueous solution has been confirmed by (1)H NMR spectroscopy performed on the diamagnetic 1-SbZn and 3-SbZn derivatives. Our systematic study of the reactivity of disubtituted Krebs-type polyoxotungstates toward diazole-, pyridine-, and diazinecarboxylates demonstrates that organic derivatization is strongly dependent on the nature of the ligand, as follows: imc displays a "universal ligand" character, as functionalization takes place regardless of the external 3d metal and heteroatom; pzc and pyzc show selectivity toward specific 3d metals; pyridazine-3-carboxylate and pyrimidine-4-carboxylate promote partial decomposition of specific precursors, leading to [M(II)L2(H2O)2] complexes; and picolinate is inert under all conditions tested.

Crystal structure of trans-di-aqua-bis-(1H-pyrazole-3-carboxyl-ato-κ(2) N,O)copper(II) dihydrate.

In the title compound, [Cu(C4H3N2O2)2(H2O)2]·2H2O, the Cu(II) ion is located on an inversion centre and exhibits an axially elongated octa-hedral coordination geometry. The equatorial plane is formed by two N,O-bidentate 1H-pyrazole-3-carboxyl-ate ligands in a trans configuration. The axial positions are occupied by two water mol-ecules. The mononuclear complex mol-ecules are arranged in layers parallel to the ab plane. Each complex mol-ecule is linked to four adjacent species through inter-molecular O-H⋯O and N-H⋯O hydrogen bonds that are established between the coordinating water mol-ecules and carboxyl-ate O atoms or protonated N atoms of the organic ligands. These layers are further connected into a three-dimensional network by additional hydrogen bonds involving solvent water mol-ecules and non-coordinating carboxyl-ate O atoms.