Anderson-type Heteropolyanion Research Articles

Mechanistic insights into aerobic oxidative cleavage of glycol catalyzed by an Anderson-type polyoxometalate [IMo6O24]5.

A computational investigation of the aerobic oxidative C-C bond cleavage reaction of glycol catalyzed by an Anderson-type heteropolyanion HPA [IMo6O24]5- in the presence of acetonitrile as solvent has been performed at the WB97XD/6-31G(d,p)/lanl2dz level. Two reaction pathways have been identified. The catalytic cycle of each pathway consists of three steps: oxidation cleavage of a glycol molecule by the HPA, oxidation of the HPA by one dioxygen molecule, and, finally, oxidation of a second glycol and regeneration of the catalyst. These reaction pathways have been thoroughly investigated in terms of energetic, natural bond orbital (NBO), natural charges, and geometrical parameters. It is found that (i) even though the top oxygen atoms of the Anderson heteropolyanion are not the most negatively charged ones, they are more likely to react with the diol hydroxyl groups, (ii) a direct relationship between the presence of the iodine ion I(VII) and the studied oxidation reaction could not be identified, and (iii) in terms of energy, the transfer of the two hydrogen atoms is the most energetic step.

Synthesis, crystal structure and optical properties of Anderson-type heteropolyanion with cobalt cations

A sample inorganic A-type Anderson polyoxometalate (POM) (TeMo6) compound formulated as [Co(H2O)6]3[TeMo6O24] is synthesized in aqueous solution by slow evaporation technique. Single-crystal X-ray diffraction analysis reveals that the obtained compound crystallizes in the centrosymmetric hexagonal space group (R-3c) with a formula unit made up of one [TeMo6O24]6− A-type Anderson anion and three [Co(H2O)3]2+ cations. The molecular Hirshfeld surface indicates that the crystal packing is stabilized by H-bonds interactions to generate 3D supramolecular frameworks. Furthermore, some optical properties such as bandgap energy, refractive index, dielectric constant and optical conductivity of the sample are investigated. The large value of refractive index known in the visible region of electromagnetic spectrum (n = 3.5 at 1.8 eV) reveals that this sample can become a promising candidate for visible optical communication devices. The emission fluorescent spectrum in the solid state at room temperature is measured and the decay lifetime curves are obtained by monitoring the ligand-to-metal charge transfer transition (LMCT). The studies of the colorimetric properties of the sample reveal that the color coordinates (x = 0.33667; y = 0.25564) are located in the region of National Television System Committee (NTSC) in the CIE chromaticity chart and the calculated correlated color temperature value (CCT ~ 5085 K) indicates that the optimized compound could be applied as a cool light emission diode.

Use of Rh (III)-Heteropolymolybdate as Potential Catalysts for the Removal of Nitrates in Human Drinking Water: Synthesis, Characterisation and Catalytic Performance

The investigation and development of technologies to remediate water contaminated with NO3− are constantly increasing. An economically and potentially effective alternative is based on the catalytic hydrogenation of NO3− to N2. With this objective, bimetallic RhMo6 catalysts based on Anderson-type heteropolyanion (RhMo6O24H6)3− were prepared and characteri3ed in order to obtain well-defined bimetallic catalyst. The catalysts were supported on Al2O3 with different textural properties and on silica. The heteropolyanion-support interaction was analysed by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The differences obtained in activity and selectivity to the different products can be assigned to the different interaction between the RhMo6 Anderson phase and the supports. The RhMo6/G, (G: γ-Al2O3) system showed the best catalytic performance. This catalyst exhibited the lowest reduction temperature of Rh and Mo in the TPR assay and a Rh/Mo surface ratio similar to that of the original phase, as observed by XPS analysis. These studies allowed us to verify a synergic effect between Rh and Mo, through which Mo reducibility was promoted by the presence of the noble metal. The catalytic activity was favoured by the active sites generated from the Anderson phase. This fact was confirmed by comparing the activity of RhMo6/G with that corresponding to a conventional catalyst prepared through successive impregnation of both Rh (III) and Mo (VI) salts.

Application of Magnetic Resonance Imaging and Raman Imaging to study the impact of phosphorus in impregnation of hydrotreatment catalysts

Magnetic Resonance Imaging is applied, for the first time, to monitor in-situ the impregnation step of hydrotreatment catalysts with an aqueous solution composed simultaneously of molybdenum, cobalt and phosphorus. This technique provides information about spatial distribution of all metal precursors inside the catalyst pellet with a significantly improved spatial resolution of 39μm×39μm compared to the literature. Streamline Raman Imaging yields complementary information about molybdenum speciation at equilibrium. For a molybdenum based catalyst, a slow transport of molybdenum complexes through γ-alumina is observed by Magnetic Resonance Imaging, which suggests a strong interaction between metal precursor and the support. Presence of polymeric molybdenum ions is found near the edges as well as the formation of an Anderson-type heteropolyanion. In the presence of phosphorus, interaction between molybdenum and γ-alumina is weaken since a preferential adsorption to phopshorus is observed. This phenomenon results in an increase in the transport rate of molybdenum complexes. When phosphorus is added to a molybdenum based catalysts promoted by cobalt, preferential interactions between metal promotor and the support are observed rather than with molybdenum species. This innovative Magnetic Resonance Imaging −Streamline Raman Imaging methodology allows a better control of the deposition process during impregnation and to identify the descriptors that most influence this preparation step. Finally, this methodology can be applied to other type of supported catalysts.

Influence of the Preparation Conditions of Oxidic NiMo/Al2O3 Catalysts on the Sulfidation Ability: A Quick-XAS and Raman Spectroscopic Study

The structure of oxidic precursors of supported NiMo hydrodesulfurization catalysts has been investigated in-depth by the combination of laser Raman spectroscopy and X-ray absorption spectroscopy measured at the Mo and Ni K edges at the different stages of the preparation. The oxidic catalysts were prepared by incipient wetness impregnation of δ-alumina with a solution obtained by dissolving MoO3 in H2O2 and subsequently adding Ni(NO3)2·6H2O in this as-prepared solution (8 wt % MoO3; 2 wt % NiO). The formation of the 6-molybdoaluminate Anderson-type heteropolyanion (AlMo6O24H6)3– and of a mixture of oxo–hydroxo nickel species and bulk and/or surface NiAl-layered double hydroxide dispersed at the surface of the support has been identified after drying. Upon further thermal treatment at 723 K under dried air, calcined dehydrated catalyst is constituted of highly distorted isolated or partially condensed tetrahedral Mo units with terminal mono-oxo groups and of bulk and/or surface NiAl2O4-type and NiO-type s...

Coordination of lanthanide cation to an Anderson type polyoxometalate anion leads to isomorphous metal-oxide based one-dimensional inorganic solids: Synthesis, crystal structure and spectroscopy

One-dimensional isomorphous inorganic polymers containing Anderson type heteropoly anion as a basic building unit, namely [La(H2O)7Cr(OH)6Mo6O18]n⋅4nH2O (1), [Gd(H2O)7Cr(OH)6Mo6O18]n⋅4nH2O (2), [Gd(H2O)7Al(OH)6Mo6O18]n⋅4nH2O (3), and [Eu(H2O)7Al(OH)6Mo6O18]n⋅4nH2O (4) have been synthesized and studied by the powdered X–ray diffraction, TGA, IR, electronic and ESR spectroscopy, and unambiguously by single crystal X-ray crystallography. Isomorphous compounds 1-4 are crystallized in orthorhombic system with Pca2 1 space group. The crystal structure analysis reveals a one-dimensional extended chain in which the Anderson type heteropolyanion, acting as the building unit, is linked by rare earth metal ions in a zig-zag fashion. In the crystal structure, all types of oxygens of the heteropolyanion, lattice waters, lanthanum coordinated waters are extensively involved in O—H ⋯O hydrogen bonding interactions. Compounds are additionally characterized by UV-visible and ESR spectroscopy. A series of four one-dimensional isomorphous inorganic solids namely, [La(H2O)7Cr(OH)6Mo6O18]n•4nH2O (1), [Gd(H2O)7Cr(OH)6Mo6O18]n•4nH2O (2), [Gd(H2O)7Al(OH)6Mo6O18]n•4nH2O (3), and [Eu(H2O)7Al(OH)6Mo6O18]n•4nH2O (4) have been synthesized and characterized by the powdered X–ray diffraction studies, TG analysis, IR-, electronic- and ESR-spectroscopy, and unambiguously by single crystal X˗ray crystallography.

Bis(amino{[iminio(morpholino)methyl]amino}iminium) bis(amino{[imino(morpholino)methyl]amino}iminium) tetracosaoxidotellurohexamolybdate(6−) tetrahydrate

The title compound, (H2ABOB)2(HABOB)2[TeVIMoVI6O24]·4H2O, consists of an Anderson-type heteropolyanion, [TeVIMoVI6O24]6−, two monoprotonated ABOB cations, two diprotonated ABOB cations and four water mol­ecules (ABOB = N-amidino-4-morpholincarboxamidine). The hetero­polyanion [TeVIMoVI6O24]6− is located on an inversion center. Electrostatic forces and hydrogen-bonding inter­actions among the [TeVIMoVI6O24]6−anions, the water mol­ecules and the ABOB cations result in a three-dimensional supra­molecular structure.

Comparison between optimized geometries and vibrational frequencies calculated by the DFT methods for the Anderson-type heteropolyanion: Hexamolybdoaluminate(III), [Al III(OH) 6Mo 6O 18] 3−

Optimized geometries and vibrational frequencies were calculated for the hexamolybdoaluminate(III), [Al III(OH) 6Mo 6O 18] 3−, Anderson-type heteropolyanion with the HF, B3LYP, B3PW91, B3P86 and B1LYP methods of theory using the LanL2DZ, SDD and combination of LanL2DZ with 6-31G (d, p) basis sets. The agreement between the optimized and experimental geometries was in the decreasing order: HF, B3P86, B3PW91, B1LYP and B3LYP. The calculated frequencies by the B3LYP have the smallest mean root mean square (RMS) error. The effect of the basis set on the calculated bond lengths and frequencies by the density functional calculations (DFT) methods was minor. The agreement between the previously reported IR and Raman spectra and the calculated values is, in general, good.

Density functional theory and Hartree–Fock studies: Geometry, vibrational frequencies and electronic properties of Anderson-type heteropolyanion, [XM 6O 24] n− (X = Te VI, I VII and M = Mo, W) and [Sb VW 6O 24] 7−

The geometry, IR and Raman spectra and electronic properties of Anderson-type heteropolyanions with main-group high oxidation state heteroatom, [Te VIMo 6O 24] 6−, [I VIIMo 6O 24] 5−, [Sb VW 6O 24] 7−, [Te VIW 6O 24] 6− and [I VIIW 6O 24] 5− have been investigated using Hartree–Fock (HF) and density functional theory (DFT) methods. HF method has good results in geometry parameters but poorer than DFT method in the results of vibrational frequencies. Also we have investigated the effect of LanL2DZ augmented in the vibrational frequencies. With attention to relative charge and size of the cavity occupied by XO 6 subunit in these anions, we suggest that the general formula [XO 6 n− @M 6O 18] to describe electronic properties of these anions.

A novel polyoxometalate chain formed from heteropolyanion building blocks and rare earth metal ion linkers: [La(H2O)7Al(OH)6Mo6O18]n·4nH2O

The structure of the complex [La(H2O)7Al(OH)6Mo6O18]n·4nH2O is the first example of a 1D extended chain in which an Anderson type heteropolyanion is linked by rare earth metal ions in zig-zag chains that arrange “head to tail” in the structure; furthermore the chains are themselves linked into an extensive three-dimensional hydrogen bonded network.

The structure of the hexamolybdoperiodate anion in its potassium salt

Ks[IMo6024]. 5H20, P i , a = 10.084 (1), b = 17.593(2), c = 7.692(1) A, a = 95.07(1), fl = 91.38 (1), y = 82.45 (1) °, U = 1347-5 (2) A 3, FW = 1372.10, Z = 2, D m = 3.37, D x = 3.42 Mg m -3, a = 4.375 mm -1 (for Mo Ka). The [IMo6024] 5anion has been found to be a typical Anderson-type heteropolyanion and has approximate 3m symmetry. The meta l oxygen bond lengths in this anion and in [TeMo6024] 6show the difference between the 17+-O and Te6+-O bond strengths. 0567-7408/80/030661-04501.00 Introduction. Many Keggin-type heteropolyanions have been studied; there is also another group of heteropolyanions called the Anderson type (Anderson, 1937). The latter type of polyanion consists of seven octahedra sharing edges with one another. Six Mo octahedra are arranged hexagonally around the octahedron containing the heteroatom. A number of examples of the preparations of Anderson-type polyanions have been reported (Gmelins Handbuch der Anorganischen Chemic, © 1980 International Union of Crystallography 662 THE HEXAMOLYBDOPERIODATE ANION IN ITS POTASSIUM SALT 1935), but fewer structural studies have been carried out (Evans, 1974; Perloff, 1970). The present structure was originally proposed by Anderson (1937) for this [IMo6024] 5anion. This paper reports its structure determination and the structure is compared with that of [TeMotO24 ]6-. Preparations of the periodatomolybdates have been described by Blomstrand (1892). The intensities of the reflections were measured with a Rigaku automatic four-circle diffractometer (graphite monochromator, Mo Ka radiation, w--20 scan technique) up to 20 = 65 ° . The intensities of 6627 observed independent reflections, with IFol > 3tr(IFol), were used for the structure determination. The dimensions of the crystal were 0.3 × 0-1 x 0.05 mm. The structure was solved by the heavy-atom method, except for the H atoms, and refined by the block-diagonal least-squares method. Calculations were performed with a local version of UNICS (Sakurai, 1967) on a HITAC 8800/8700 computer at the Computer Centre of the University of Tokyo. Anisotropic temperature factors were used for all the non-hydrogen atoms. Atomic scattering factors and corrections for anomalous scattering were taken from International Tables for X-ray Crystallography (1974). No absorption correction was made. The function minimized was ~ w(IFol IFcl) 2, where w = l/(a + IFol + clFo 12) with a = 43.03 and c = 0.00469 estimated experimentally according to Cruickshank (1970), for IFol > 21.0, and w = 0.122 for others. The final R values are Rw(F) = 0.050 and R(F) = 0.047, where R w ( F ) --~ wilFol -IFcll/~ WlFol and R ( F ) --X IIFolIF<ll/X iFoi. Atomic fractional coordinates and averaged bond distances and angles are listed in Tables 1 and 2.* Table 1. Fractional coordinates (x 104)