Heterogeneous amino acid-based tungstophosphoric acids as efficient and recyclable catalysts for selective oxidation of benzyl alcohol

A series of organic-inorganic composite catalysts, prepared by modifying tungstophosphoric acid (TPA; H₃PW₁₂O₄₀) with different amino acids such as phenylalanine (Phe), alanine (Ala), and glycine (Gly) were synthesized. The physicochemical and acidic properties of these (MH) _x H_3?x PW₁₂O₄₀ (M=Phe, Ala, and Gly; x=1–3) composite materials were characterized by a variety of different analytical and spectroscopic techniques, namely TGA, XRD, FT-IR, XPS, and NMR, and exploited as heterogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H₂O₂). Among them, the [PheH]H₂PW₁₂O₄₀ catalyst exhibited the best oxidative activity with an excellent BzOH conversion of 99.0% and a desirable benzaldehyde (BzH) selectivity of 99.6%. Further kinetic studies and model analysis by response surface methodology (RSM) revealed that the oxidation of BzOH with H₂O₂ follows a second-order reaction with an activation energy of 56.7 kJ·mol^?1 under optimized experimental variables: BzOH/H₂O₂ molar ratio=1 : 1.5 mol/mol, amount of catalyst=6.1 wt%, reaction time (x₃)=3.8 h, and amount of water (x₄)=30.2 mL.     

Synthesis and single-crystal structure of lead oxide nanoclusters in zeolite Y, |Pb 15.5 2+ (Pb4O4(Pb 16/19 2+ Pb 3/19 4+ )4)4.75|[Si117Al75O384]-FAU

A single crystal of excessively Pb²⁺-exchanged zeolite Y (|Pb _15.5 ²⁺ (Pb₄O₄(Pb _16/19 ²⁺ Pb _3/19 ⁴⁺ )₄)_4.75|[Si₁₁₇Al₇₅O₃₈₄]-FAU) was prepared by exchange of Na–Y (|Na₇₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU, Si/Al = 1.56) with an aqueous stream 0.05 M Pb(C₂H₃O₂)₂ at 294 K, followed by vacuum dehydration at 1 × 10^?6 Torr and 693 K. Its structure was determined at 100 K, by X-ray diffraction techniques in the cubic space group Fd $ \overline{3} $ 3 ¯ m and was refined to the final error indices R ₁/wR ₂ = 0.0639/0.1323. About 53.5 Pbⁿ⁺ ions per unit cell occupy three different equipoints; 26 are at site I′, 19 are at site II, and the remaining 8.5 are at another site II. Three Pb⁴⁺ ions at some of the positions must have higher oxidation states due to elevated dehydration temperature; Pb(IIa) is supposed to coexist with Pb²⁺ and Pb⁴⁺ ions assuming the charge balance of the zeolite framework. A distorted Pb₄O₄ cube, alternating Pb²⁺ at Pb(I′) and O^2? at O(5), coordinates with four Pb²⁺ and/or Pb⁴⁺ ions through its oxygen atoms to give a [Pb ₄ ²⁺ O ₄ ^2? (Pb _16/19 ²⁺ Pb _3/19 ⁴⁺ )₄]^176/19+ cluster in 4.75 of eight sodalite cavities per unit cell in zeolite Y.     

One-pot generation of mesoporous carbon supported nanocrystalline H3PW12O40 heteropoly acid with high performance in microwave esterification of acetic acid and isoamyl alcohol

Ordered mesoporous carbon-supported H₃PW₁₂O₄₀ heteropoly acid materials (HPW/OMCs) have been rationally synthesized for the first time. The method is based on the evaporation-induced triconstituent co-assembly effect using the sol–gel process, wherein soluble resol polymer is used as an organic precursor, and triblock copolymer F127 is used as a template. The ordered mesoporous carbon-supported H₃PW₁₂O₄₀ heteropoly acid materials were analyzed and characterized by X-ray diffraction, N₂ adsorption and desorption (BET), and transmission electron microscope. The mesoporous carbon-supported H₃PW₁₂O₄₀ materials possess an ordered mesostructure, narrow pore size distributions (around 2.8–3.6 nm), high pore volumes (up to 0.49 cm³ g^?1), high specific BET surface areas (up to 590 m² g^?1), tailorable HPW content (up to 30 wt%), and well dispersion of HPW particles. Moreover, the resultant mesoporous ordered mesoporous carbon-supported H₃PW₁₂O₄₀ materials exhibit high catalytic activity in microwave esterification of acetic acid and isoamyl alcohol. The obtained 20 % HPW/OMC catalyst exhibits high catalytic performance with 96.7 % of isoamyl acetate yield at temperature of 120 °C, alcohol/acid molar ratio of 2, catalyst amount of 0.2 g, microwave irradiation power of 800 W, and reaction time of 18 min. It was believed that the concentration of H₃PW₁₂O₄₀ have a crucial effect on the HPW/OMCs’ porosity, mesostructure and catalytic performance.     

Organosoluble and thermally stable modified poly(ether-imide-urethane)s bearing benzoxazole or benzothiazole pendent groups: synthesis and characterization

Preparation of new types of modified poly(ether-imide-urethane)s, P _O a-c and P _S a-c, with good thermal stability and improved solubility was investigated. Two new bis(ether-azide)s bearing benzoxazole or benzothiazole pendent groups were synthesized by treating 2-[3,5-bis(4-trimellitimido-phenoxy)-phenyl]benzoxazole (1 _O ), or 2-[3,5-bis(4-trimellitimido-phenoxy)-phenyl]benzothiazole (1 _S ) with ethyl chloroformate in the presence of triethylamine, and subsequent by a nucleophilic reaction with sodium azide, respectively. Two series of modified polymers with moderate inherent viscosities between 0.21 and 0.32 dL g^?1 were prepared from bis(ether-azide)s 2 _O and 2 _S with several aromatic diols in dry toluene under refluxing in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO, triethylenediamine) as a catalyst. The polycondensation reaction readily proceeded in desirable yields as one-pot reactions starting from 2 _O to 2 _S without the separate synthesis of the corresponding bis(ether-isocyanate)s. In addition, the corresponding unsubstituted poly(ether-imide-urethane)s, P _R a-c, were prepared under identical experimental conditions for comparative purposes. All of the resulted polymers were thoroughly characterized by spectroscopic methods and thermogravimetry. The solubilities of modified polymer in common organic solvents as well as their thermal stability were enhanced compared to these of the corresponding unmodified polymers. The glass transition temperature, 10 % weight loss temperature and char yields at 800 °C were, respectively, 13–28 °C, 19–32 °C and 3–7 % higher than those of the unmodified polymers.     

Direct and improved synthesis of the tri-nickel sandwich-type polyoxoanion [Ni3Na(H2O)2(PW9O34)2]11−

The direct use of preformed B,α-Na₉PW₉O₃₄ was successful in improving the synthesis of Na₁₁[Ni₃Na(H₂O)₂(PW₉O₃₄)₂]·14H₂O. The complex was characterized by elemental analysis, IR spectroscopy, magnetic properties and cyclic voltammetry. The yield was increased to 30%, which is four times more than that obtained in the initial synthesis. The delay before the appearance of the first crystals is drastically shortened, from months to hours, and these crystals are predominantly those of the yellow compound of interest. Keys to these improvements are the use of freshly prepared B,α-Na₉PW₉O₃₄ through prolonged heating of A,β-Na₉PW₉O₃₄ and the increase of the concentrations of the reactants in a close-to-neutral pH medium. Starting the synthesis with several concentrations of preformed A,β-Na₉PW₉O₃₄ revealed the importance of the concentrations of reactants in speeding up the formation of crystals and suggested strongly that the [A-PW₉O₃₄]⁹⁻→[B-PW₉O₃₄]⁹⁻ isomerization might be the slow step in the whole process. Cyclic voltammograms as well as X-ray diffraction structure determination confirm that the synthesized compound is indeed Na₁₁[Ni₃Na(H₂O)₂(PW₉O₃₄)₂]·14H₂O. A study of the magnetic properties of Na₁₁[Ni₃Na(H₂O)₂(PW₉O₃₄)₂]·14H₂O indicates that the three nickel centres exhibit ferromagnetic exchange interactions.     

Crystal Structures and Luminescent Properties of Two Lanthanide(III) Complexes Featuring Double-Stranded Helical Chains of Based on 2-Sulfoterephthalate

Hydrothermal reaction of Eu³⁺ and Dy³⁺ salts with monosodium 2-sulfoterephthalate (NaH₂stp) gives two 2D lanthanide coordination polymers, [Ln(stp)(H₂O)₂] _n (Ln = Eu (1) and Dy (2)). Single-crystal X-ray diffraction of the complexes reveal that both 1 and 2 crystallize in the triclinic crystal system of Pī space group. For 1, each Eu³⁺ ion lies in a 9-coordinated slightly distorted tri-capped triangle pyramidal configuration. The stp ligands adopt a μ ₄-type link to the metal ions to form a 2D layer-like structure, of which there exist the left- and right-handed double-stranded helical chains. For 2, each Dy³⁺ ion is in a 8-coordinated distorted bi-capped triangle pyramidal geometry. The double-stranded helical chains in 2 differ from those in 1. The thermal stabilities of the two compounds are studied by TGA. The solid state photoluminescence of 1 and 2 are reported. The fluorescent decay curves of the ligand and compounds indicate that 1 has the lifetime of 286.7 μs, τ ₁ = 0.51 ns and τ ₂ = 3.07 ns for the ligand, and for 2, τ ₁ = 0.53 ns and τ ₂ = 2.71 ns.     

Three-Dimensional Structure of Barium–Cupric Nitrilotriacetate and One-Dimensional Structure of Cobalt–Cupric Nitrilotriacetate: Template Effect of Cations on the Formation of Coordination Polymers

Three mixed-metal nitrilotriacetates [Ba(H₂O)₃Co(nta)Cl]_n (1), [Ba(H₂O)₃Ni(nta)Cl]_n (2), and [Ba(H₂O)₃Cu(nta)Cl]_n (3) (H₃nta = nitrilotriacetic acid) were prepared by the reaction of M²⁺ ions (M = Co, Ni, and Cu), K₃nta, and Ba²⁺ ions in water. The reaction of complexes 1 and 2 with CuSO₄·5H₂O afforded [Co(H₂O)₆]_n[Cu₂(nta)₂]_n·2nH₂O (4) and [Ni(H₂O)₆]_n[Cu₂(nta)₂]_n·2nH₂O (5), respectively. The reaction mechanism was elucidated. The crystal structure analyses indicate that the Ba²⁺ ions formed one-dimensional (1D) zigzag chains in complex 3, and the chains were connected by Cu(nta)^? anions to form a three-dimensional network. On the other hand, in complexes 4 and 5, the Cu(nta)^? anions formed 1D zigzag chains, and the [Co(H₂O)₆]²⁺ (or [Ni(H₂O)₆]²⁺) cations existed as isolated units.     

The dependence of Co2+-exchange into zeolite FAU on its Si/Al ratio

Three single crystals of fully dehydrated, largely Co²⁺-exchanged zeolites X and Y were prepared by the exchange of Na₈₀-X (|Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU, Si/Al = 1.40), Na₇₅-Y (|Na₇₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU, Si/Al = 1.56), and Na₇₁-Y (|Na₇₁|[Si₁₂₁Al₇₁O₃₈₄]-FAU, Si/Al = 1.70) with aqueous streams 0.05 M in Co(NO₃)₂, pH = 5.1, at 294 K for 3 days. This was followed by vacuum dehydration at 673 K. Their crystal structures were determined by synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{3}\) m at 100(1) K. In all three crystals Co²⁺ ions occupy the 6-ring sites I, I’, and II; Na⁺ ions occupy sites II’ and II. The number of Co²⁺ ions exchanging into the zeolite was about 30 per unit cell for all three crystals. The number of residual Na⁺ ions, however, decreased sharply as Si/Al ratio increased, and the number of H⁺ ions co-exchanging into the zeolite decreased nearly to zero. Some dealumination of the zeolite framework was seen in the first crystal (initial Si/Al = 1.40).     

Ancillary Ligand-Mediated Syntheses,Structures and Fluorescence of Three Zn/Cd(II) Coordination Polymers Based on Nitrobenzene Dicarboxylate

The Zn/Cd(II)-nbdc carboxylate motifs mediated by various dipyridyl-typed ligands afforded three new coordination compounds, namely, [Zn(nbdc)(bpa)_0.5(H₂O)]·H₂O (1), [Zn₂(nbdc)₂(bpp)₂]·H₂O (2), and [Cd(nbdc)(bpe)_0.5(H₂O)₂] (3) (H₂nbdc = 4-nitrobenzene-1,2-dicarboxylic acid, bpa = 1,2-bi(4-pyridyl)ethane, bpe = 1,2-di(4-pyridyl)ethylene, and bpp = 1,3-bis(4-pyridyl)propane), which were synthesized by hydrothermal reaction and characterized by elemental analysis, IR, thermal analysis (TGA), and fluorescent analysis. The single-crystal X-ray diffractions reveal that three complexes display a diverse range of connectivity topology from 1D to 3D, which is dependent on the type of dipyridyl-typed ligands and metal centers. Complex 1 is the 1D chain featuring Zn-carboxylate binuclears extended further by bpa coligands. Complex 2 is the 2D thick-layer containing double-stranded chains cross-linked further by bpp coligands. Complex 3 is the 3D framework with (6³)(6⁵.8) ins topology featuring Cd-carboxylate chiral layers pillared by bpe coligands. The thermal stabilities and fluorescence properties for complexes 1–3 are investigated.     

New Environmentally Friendly Oxidative Scission of Oleic Acid into Azelaic Acid and Pelargonic Acid

Oleic acid (OA) is a renewable monounsaturated fatty acid obtained from high oleic sunflower oil. This work was focused on the oxidative scission of OA, which yields a mono-acid (pelargonic acid, PA) and a di-acid (azelaic acid, AA) through an emulsifying system. The conventional method for producing AA and PA consists of the ozonolysis of oleic acid, a process which presents numerous drawbacks. Therefore, we proposed to study a new alternative process using a green oxidant and a solvent-free system. OA was oxidized in a batch reactor with a biphasic organic-aqueous system consisting of hydrogen peroxide (H₂O₂, 30 %) as an oxidant and a peroxo–tungsten complex Q₃{PO₄[WO(O₂)₂]₄} as a phase-transfer catalyst/co-oxidant. Several phase-transfer catalysts were prepared in situ from tungstophosphoric acid, H₂O₂ and different quaternary ammonium salts (Q⁺, Cl^–). The catalyst [C₅H₅N(n-C₁₆H₃₃)]₃{PO₄[WO(O₂)₂]₄} was found to give the best results and was chosen for the optimization of the other parameters of the process. This optimization led to a complete conversion of OA into AA and PA with high yields (>80 %) using the system OA/H₂O₂/[C₅H₅N(n-C₁₆H₃₃)]₃{PO₄[WO(O₂)₂]₄} (1/5/0.02 molar ratio) at 85 °C for 5 h. In addition, a new treatment was developed in order to recover the catalyst.     

Preparation, Crystal Structures and Photoluminescence of Two New Zinc Complexes Based on 1H-Imidazo[4,5-f][1,10]-phenanthroline and Auxiliary Ligands

Two new coordination polymers [Zn(ip)(2,5-tda)(H₂O)₂] _n (1) and [Zn₂(ip)₂(5-npa)₂] _n (2) (2,5-tda = thiophene-2,5-dicarboxylic acid, ip = 1H-imidazo[4,5-f][1,10]-phenanthroline and 5-npa = 5-Nitroisophthalic acid) were synthesized and characterized by IR, elemental analysis, PXRD and X-ray diffraction. Single-crystal X-ray analyses revealed that 1 and 2 demonstrate a 1D chain structure. Complex 1 was bridged by 2,5-tda ligands in a μ₁ ? η¹:η⁰/μ₁ ? η¹:η⁰ coordination mode, and further extended into a 2D supramolecular structure by hydrogen bonding and π···π interactions. In 2, the 5-npa ligand acts as a bridging moeity, exhibiting μ₁ ? η¹:η¹/μ₁ ? η¹:η⁰ and μ₁ ? η¹:η⁰/μ₁ ? η¹:η⁰ coordination modes to link metal ions to form a 1D chain. The chains are further connected via hydrogen bonding interactions into a 2D supramolecular structure. The luminescent properties for 1 and 2 were investigated in the solid state at room temperature.     

A Strategy for Preparing Star Polymers Containing Metal–Metal Bonds Along the Polymeric Arms Using Click Chemistry

The [(η⁵-C₅H₄(CH₂)₃N₃)Mo(CO)₃]₂ dimer (3) was prepared and used to determine if the Huisgen cycloaddition reaction could be used to synthesize high molecular weight star polymers with metal–metal bonds in the arms. Several different click catalysts were examined. Cp*Ru(PPh₃)₂Cl (Cp* = η⁵-C₅(CH₃)₅) was previously shown to catalyze the formation of metal–metal bond-containing polymers using click chemistry; however, this catalyst underwent a Staudinger reaction with dimer 3 when a model coupling reaction was attempted with phenylacetylene. In order to avoid the Staudinger reaction, Cp*Ru(COD)Cl was used as the catalyst in the reaction of 3 with phenylacetylene, and coupling was observed after 14 h. Synthesis of a star polymer was attempted with 3 and 1,3,5-triethynylbenzene. Instead of coupling, Cp*Ru(COD)Cl reacted with the 1,3,5-triethynylbenzene. A third catalyst, Cu(IMes)Cl (IMes = 1,3-dimesityl-imidazol-2-ylidene) was used to couple 3 with 1,3,5-triethynylbenzene in 48 h. Both a high molecular weight polymer (M _n  = 77,000 g mol^?1) and a tripodal star core (M _n  = 1,800 g mol^?1) were successfully prepared with this catalyst.     

Selective ammoximation of ketones and aldehydes catalyzed by a trivanadium-substituted polyoxometalate with H2O2 and ammonia

The ammoximation of different ketones and aldehydes to their corresponding oximes catalyzed by K₆[PW₉V₃O₄₀]·4H₂O was carried out with hydrogen peroxide and ammonia in isopropanol at room temperature. High yields of oximes were obtained in this catalytic system. This catalytic system was proved to be heterogeneous by the ammoximation activity of removal of catalyst and the elemental analysis of the filtrate after reaction. A possible procedure for the ammoximation catalyzed by K₆[PW₉V₃O₄₀]·4H₂O with H₂O₂ and NH₃·H₂O was proposed. The fresh and used catalysts were characterized by IR and ³¹P MAS NMR, which revealed the good stability of the catalyst.     

Effect of surface hydroxyl groups of pure TiO2 and modified TiO2 on the photocatalytic oxidation of aqueous cyanide

It is still debatable whether the photocatalytic oxidation of cyanide proceeds via hydroxyl radicals or by photogenerated holes. We synthesized pure TiO₂ catalysts via sol-gel process. In order to elucidate the oxidation pathway of cyanide, we used hydroxyl radical scavengers and controlled the concentration of surface hydroxyl group on the catalysts adopting fluoride-exchange. The degree of fluoride-exchange of TiO₂ catalysts was independent of the pH of suspension. We also adopted a polyoxometalate, tungstophosphoric acid (TPA, H₃PW₁₂O₄₀) which is well known for high charge transfer ability and hydrolytic stability. TPA-modified TiO₂ catalysts were prepared with sol-gel technique to overcome the high solubility of TPA in water. As another attempt for the insoluble TPA, proton of TPA supported on TiO₂ catalysts was replaced by cesium ion to form Cs-TPA/TiO₂ catalysts. Both attempts were successful in immobilizing TPA on TiO₂ catalysts. Commercially available TiO₂ catalysts such as P25 from Degussa AG were also used as catalysts. XRD analysis revealed that pure TiO₂ and TPA-modified TiO₂ catalysts prepared by sol-gel process were composed of well-developed anatase crystalline structure. In the presence of hydroxyl radical scavengers, the photoactivity of TPA-modified TiO₂ catalysts was retarded much less than that of pure TiO₂ catalysts. The concentration of surface hydroxyl group was effectively suppressed by the fluoride-exchange causing the decrease of the activity of the catalysts. In the case of fluoride-exchanged catalysts, the drop in activity was obvious for the pure TiO₂ catalysts in the presence of iodide as a hydroxyl radical scavenger suggesting that indirect oxidation via hydroxyl radicals was the preferential reaction pathway. For the TPA-modified TiO₂ catalysts, meanwhile, the diminution was such a small extent suggesting that direct oxidation by photogenerated holes was the main reaction pathway. The activity arising from TPA in the catalysts was due to the Keggin structured anion (PW₁₂O ₄₀ ^3- ) which acted as an electron relay with the aid of dissolved oxygen in the reaction system. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Preparation and structural study of fully dehydrated,highly Mg2+-exchanged zeolite Y (FAU,Si/Al = 1.56) from undried methanol solution

Single-crystal of fully dehydrated, Mg²⁺-exchanged zeolite Y, |Mg_34.5Na₆|[Si₁₁₇Al₇₅O₃₈₄]-FAU (Si/Al = 1.56), was successfully prepared from undried methanol solution (water concentration 0.02 M). A crystal of Na-Y was treated with 0.05 M MgCl₂ ·6H₂O in the solvent at 333 K, followed by vacuum dehydration at 723 K and 1 × 10^?6 Torr for 2 days. Its structure was determined by single-crystal synchrotron X-ray diffraction techniques, in the cubic space group \(Fd\overline{3} m\) at 100 K. It was refined to the final error indices R ₁/wR ₂ = 0.0587/0.2210 with 1,294 reflections for which F _o > 4σ(F _o). In the structure of |Mg_34.5Na₆|[Si₁₁₇Al₇₅O₃₈₄]-FAU, 34.5 Mg²⁺ ions per unit cell are found at four different crystallographic sites: 15 per unit cell are located at site I at the center of the hexagonal prism [Mg–O = 2.216(2) Å], two are at site I’ in the sodalite cavity near the hexagonal prism [Mg–O = 2.20(3) Å], only one is located at site II’ in the sodalite cavity [Mg–O = 2.197(23) Å], and the remaining 16.5 are at site II near single 6-oxygen rings in the supercage [Mg–O = 2.103(3) Å]. The residual 6 Na⁺ ions per unit cell are found at site II [Na–O = 2.218(7) Å]. No water molecules are found in this structure.     

Regeneration of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst in the direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas

Methods for regenerating H₃PW₁₂O₄₀ catalyst in the solvent-free direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas were investigated. Regenerated H₃PW₁₂O₄₀ catalyst was then applied to the solvent-free direct preparation of DCP. In the solvent-free direct preparation of DCP, selectivity for DCP over H₃PW₁₂O₄₀ catalyst regenerated by method I (recovery of solid H₃PW₁₂O₄₀ catalyst by evaporating homogeneous liquidphase product solution) significantly decreased with increasing recycling run, while that over H₃PW₁₂O₄₀ catalyst regenerated by method II (regeneration of H₃PW₁₂O₄₀ catalyst by oxidative calcination of solid product recovered by method I) was slightly decreased with no significant catalyst deactivation with respect to recycling run. On the other hand, selectivity for DCP over H₃PW₁₂O₄₀ catalyst regenerated by method III (regeneration of H₃PW₁₂O₄₀ catalyst by recrystallization and subsequent oxidative calcination of solid product recovered by method II) was the same as that over fresh catalyst without any catalyst deactivation with respect to recycling run. Thus, method III was found to be the most efficient method for the regeneration of H₃PW₁₂O₄₀ catalyst.     

A Flexible Hexacarboxylate-Samarium(III) Metal–Organic Framework: Synthesis, Structure and Spectroscopic Properties

A new flexible triazine-based polycarboxylate metal–organic framework, [Sm₂(TTHA)(H₂O)₄]·9H₂O (I) (TTHA = 1,3,5-triazine-2,4,6-triamine hexaacetate), has been synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis and FT-IR spectroscopy. Crystal data for I are monoclinic C2/c, a = 12.6974(13) Å, b = 16.7309(12) Å, c = 14.8076(15) Å, β = 91.452(8)°, V = 3,144.7(5) Å³. Each Sm^III ion is 9-coordinate in a distorted tri-capped trigonal prismatic geometry; but, the principal inorganic building block is {Sm₂O₁₆}, which comprises two of these polyhedra that share an edge. The complex exhibits a three-dimensional open-framework structure of approximately 31 % void volume, which comprises two types of channels oriented in three directions; [0 0 1], [1 1 0] and [?1 1 0]. The network can be simplified into either the cooperite (pts) or anatase (ant) topologies depending on the choice of nodes. The UV–Vis spectra of the compound are dominated by the absorption of the TTHA ligand. Thermogravimetric analysis shows that the loss of channel and coordinated water upon heating occurs in two distinct steps.     

Oxidation of Benzene Catalyzed by 2,2′-Bipyridine and 1,10-Phenantroline Cu(II) Complexes

The use of mononuclear Cu(II) 2,2′-bipyridine and 1,10-phenantroline complexes as catalysts in the oxidation of benzene, using hydrogen peroxide and tert-butyl hydroperoxide as oxidant in CH₃CN/H₂O solution is presented. The reactions were carried out at 25 and at 50 °C. The complexes [Cu(bipy)₃]Cl₂ · 6H₂O (1), [Cu(bipy)₂Cl]Cl · 5H₂O (2), [Cu(bipy)Cl₂] (3), [Cu(phen)₃]Cl₂ · 7H₂O (4), [Cu(phen)₂Cl]Cl · 5H₂O (5), [Cu(phen)Cl₂] (6) were able to oxidize benzene into phenol, hydroquinone and p-benzoquinone. Highest conversion (22%) was obtained using [Cu(Phen)Cl₂] (6) as catalyst.     

Redox Properties and Catalytic Oxidation Activities of Polyatom-Substituted H n PW11M1O40 (M = V, Nb, Ta, and W) Keggin Heteropolyacid Catalysts

Redox properties and catalytic oxidation activities of polyatom-substituted H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) Keggin heteropolyacids (HPAs) were examined. Reduction potentials and UV–visible absorption edge energies of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts in solution were determined by an electrochemical method and UV–visible spectroscopy measurements, respectively. It was observed that reduction potentials of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts increased and UV–visible absorption edge energies of the HPA catalysts decreased with decreasing electronegativity of substituted polyatom. It was also found that the lower absorption edge energy corresponded to the higher reduction potential of the HPA catalyst. Vapor-phase oxidation of benzyl alcohol was carried out as a model reaction to probe the redox properties of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, and in turn, with decreasing electronegativity of substituted polyatom. Reduction potential of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts measured by an electrochemical method and absorption edge energy of the HPA catalysts measured by UV–visible spectroscopy could be utilized as a probe of oxidation catalysis of the HPA catalysts.     

Mesoporous ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZA) mixed metal oxide as an efficient and reusable catalyst for the liquid phase <Emphasis Type="Italic">O</Emphasis>-methoxymethylation reaction under solvent free conditions

Mixed metal oxide based solid acids like ZrO₂–Al₂O₃ (ZA) with Al₂O₃ different loadings (2, 4, 6, 8 and 10 mol%) were prepared by wet impregnation method and characterized by PXRD, NH₃-TPD, BET, ICP-OES, SEM, and TEM techniques. These solid acids were evaluated for their catalytic activity in the synthesis of a series of O-methoxymethylated products under solvent-free conditions at a moderate temperature in shorter reaction time (~20 min). This is achieved by various substituted alcohols and dimethoxy methane in good yields. Solid acids containing ZA used in this study exhibited good catalytic activity in the reaction. In case of 6 mol% ZA which has highest surface acidity, surface area and catalytically active tetragonal phase was found to be highest active in the O-methoxymethylation reaction up to ~99% yield. These catalysts were found to be reactivable and reusable.