Zr K-edge XAS study on ZrO<Subscript>2</Subscript>-pillared aluminosilicate

The ZrO₂-pillared clay with high acidic property has been prepared by reacting 1 wt% colloidal suspension of Na⁺-montmorillonite with 1 N aqueous solution of ZrOCl₂·8H₂O and by subsequent heating. The evolution of local structure around zirconium of the intercalant stabilized in-between aluminosilicate layers upon intercalating, drying, and pillaring condition has been systematically studied by X-ray absorption spectroscopy, and compared to those of reference compounds such as ZrO₂, and ZrOCl₂ · 8H₂O and its 1 N aqueous solution. The intercalated zirconium species was identified as the Zr-tetramer, [Zr₄(OH)₁₄(H₂O)₁₀]²⁺, with an average molecular volume of 10 × 10 Å² and a thickness of 4.5 Å. Also it becomes more condensed upon drying and eventually transforms to a zirconium oxide pillar upon calcination.     

Unusual formations of superoxo heptaoxomolybdates from peroxo molybdates

Two novel dioxygen heptaoxomolybdates K₅[Mo₇O₂₂(O₂)(OH)]Cl·6H₂O (1) and K₅[Mo₇O₂₂(O₂)(O₂)]·8H₂O (2) were isolated from the solution of peroxo molybdate accidently. The solids were characterized by IR, EPR and X-ray single crystal analysis. Complex 1 contains a superoxo group with a short bond distance 1.27(1) Å, while 2 is a mixed complex with peroxo and superoxo groups [1.43(1), 1.27(1) Å]. All of the dioxygen groups coordinate to molybdenum atoms in side-on (η²) fashion. The two complexes are short-lived and will decompose into peroxo molybdates K₅[Mo₇O₂₁(O₂)₂(OH)]·6H₂O (3) and K₆[Mo₇O₂₂(O₂)₂]·9H₂O (4) very quickly.     

Unusual Elastic and Mechanical Behaviors of Copper Phosphate Glasses with Different Copper Valence States

Elastic and mechanical properties such as Young's modulus E, Poisson's ratio ν, Debye temperature θ_D, Vickers hardness H_v, fracture toughness K_c, and fracture surface energies γ_f of yCuO_x·(100−y)P₂O₅ glasses (y= 45, 50, 55) with different copper valence states, i.e., R(Cu⁺) = Cu⁺/(Cu⁺+ Cu²⁺), at room temperature (humidity 64%) have been examined. The following features have been found: (1) the glass transition temperature (218–434°C), H_v (2.7–4.4 GPa), E (50.6–78.2 GPa), and θ_D (358–434 K) decrease largely with increasing R(Cu⁺); (2) the mean atomic volume, K_c (0.56–1.14 MPa·m^1/2), and γ_f (1.9–11.2 J·m⁻²) tend to increase with increasing R(Cu⁺); (3) 50CuO_x·50P₂O₅ glasses with R(Cu⁺) = 0.42 and 0.55 have a high resistance against crack formation in Vickers indentation tests and no crack is observed in the 45CuO_x·55P₂O₅ glass with R(Cu⁺) = 0.57 under an applied load of about 98 N. The results demonstrate that elastic and mechanical properties of yCuO_x·(100−y)P₂O₅ glasses depend strongly on the copper valence state and the CuO_x/P₂O₅ ratio. The unusal mechanical and elastic properties of copper phosphate glasses are well explained qualitatively by considering unique oxygen coordination and bonding states of Cu⁺ ions, i.e., lower coordination number and more covalent bonding compared with Cu²⁺ ions.     

HYDROTHERMAL SYNTHESIS AND ION EXCHANGE PROPERTIES OF THE NOVEL FRAMEWORK SODIUM AND POTASSIUM NIOBIUM SILICATES

ABSTRACT

Two novel metastable sodium niobium silicates of the empirical formula: Na_l+x?yH_y(Nb_1?xSi_x)O₃ nH₂O, where x=0.33?0.38, y<l+x, n=0,7-l.l (NbSi-Na, 6.0 Å phase), and Na_3-x H_xNb₃Si₂O₁₃ nH₂O, where x<1.5, n=2.5?3.5 (NbSi-Na, 12.6 Å phase), and two novel potassium niobium silicates: K_4?xH_xNb₄SijO₂₂nH₂O, where x<l, n=3.5-4.0 (NbSi-K., 10.0 Å phase), and K_1?xH_xNbSi₄O₁₁nH₂O, where x<0.2, n=0.4-0.5 (NbSi-K, 6.05 Å phase), were synthesized in the homogeneous alkaline reaction system NbCl₅ - SiO₂ - NaOH (KOH) -H₂O₂ - H₂O under mild hydrothermal conditions. The compounds were characterized by elemental analysis, FTIR, TGA, MAS ²⁹Si NMR and X-ray diffraction. It was found that alkali metal niobium silicates have open framework structures. Their ion exchange affinity towards alkali, alkaline earth and some transition metal ions was studied. All alkali metal niobium silicates are moderately acidic ion exchangers. Both sodium niobium silicates show a distinct affinity for Cs⁺ ion among alkali metal ions, whereas potassium niobium silicate, the NbSi-K, 10.0 Å phase, exhibits affinity for Rb⁺ ion. The affinity of the sodium niobium silicate, NbSi-Na, 6.0 Å, toward strontium ion in neutral solutions is equal or superior to the best Sr-selective inorganic ion exchangers. The sodium niobium silicate (NbSi-Na, 12.6 Å phase) exhibits extremely high affinity for Pb²⁺ ion in acidic and neutral media, and both sodium niobium silicates also show a moderate affinity for Hg²⁺ ion in neutral and highly alkaline media. These exchangers could be promising for the treatment of some specific nuclear waste and contaminated environmental and biological liquors containing lead, mercury and radioactive strontium.     

Conductance and spectroscopy of protonic beta and beta″-aluminas

Five protonic beta and beta″-aluminas; viz hydrated sodium beta-alumina (1,24Na₂O·11Al₂O₃), hydronium beta-alumina (1.24H₂O·11Al₂O₃·2.6H₂O), partially dehydrated hydronium beta-alumina (1.24H₂O·11Al₂O₃·1.3H₂O), hydrogen beta-alumina (1.24H₂O·11Al₂O₃) and hydronium beta″-alumina (0.84H₂O·0.8MgO·5Al₂O₃·2.8H₂O) were examined by broad band nuclear magnetic resonance from ?196°C to 200°C. The spectra of hydronium beta-alumina and hydronium beta″-alumina are consistent with a mixed composition of H₂O, H₃O⁺ and H⁺ species in the conducting plane. Hydrogen beta-alumina and partially dehydrated hydronium beta-alumina appear to contain only relatively isolated (2.6–2.7Å) protons; no evidence of molecular water or hydronium ions is found. Water molecules intercalated into the conduction plane of sodium beta-alumina do not appear to be in rapid motion, even at 167°C, but are relatively stationary. The onset of motional narrowing in hydronium beta″-alumina occurs at ?40°C but not until +30°C in hydronium beta-alumina. This is consistent with the higher conductivity reported for hydronium beta″-alumina, 10^?3–10^?5 (ohm-cm)^?1 at 25°C, in comparison to 10^?10–10^?11 (ohm-cm)^?1 for hydronium beta-alumina at 25°C.     

Structure and in vivo anticalcification properties of a polymeric calcium–sodium–phosphocitrate organic–inorganic hybrid

This paper describes the synthesis, characterization and crystal structure of an organic–inorganic polymeric hybrid composed of Ca, Na, and phosphocitrate (CaNaPC). CaNaPC is synthesized by reaction of CaCl₂·2H₂O and Na₄(HPC)·3H₂O in water, at pH 2. Its structure is polymeric with Ca(PC)₂(H₂O) “monomers” connected through Na⁺ bridges. The 9-coordinate Ca occupies the center of an irregular polyhedron defined by four phosphate, four carbonyl, and one H₂O oxygens. CaO(C) distances are in the 2.446(2)–2.586(2) Å range. There is a short distance of 2.477(1) Å between Ca and the ester O from C–O–PO₃H₂. All –COOH groups are protonated. There are three dissociated protons per two PC molecules, all coming from –PO₃H₂. Na ions are six-coordinate surrounded by –COOH’s. The anticalcification properties of CaNaPC on plaque growth were studied in vivo using rats as model systems. Na–phosphocitrate is an effective inhibitor, but its effectiveness diminishes when a lower dose is used (9.7 mg as H₅PC), resulting in only 30% plaque reduction. Superior inhibition activity becomes evident by following treatment with CaNaPC, at an equal dose (9.6 mg as H₅PC) giving nearly quantitative (95%) plaque inhibition.     

Synthesis and structure of a high-nuclearity oxomolybdenum(V) complex, [Mo12O28(OC2H5)4(C6H7N)8]

(PyH)[MoOBr₄(H₂O)]·2/3PyHBr (PyH⁺=pyridinium cation, C₅H₅NH⁺) yielded upon the solvothermal reaction with ethanol and 4-methylpyridine (4-MePy, C₆H₇N) a novel oxoethoxomolybdenum(V) cluster, [Mo₁₂O₂₈(OC₂H₅)₄(4-MePy)₈] 1. Molybdenum atoms are grouped into six Mo^V₂ pairs linked by single metal–metal bonds. Three crystallographically independent Mo–Mo distances are 2.5578(14), 2.5981(14) and 2.6489(16) Å.     

Study of ClO2 generation reaction via experimental data of aqueous mixed electrolyte solutions: HClO4–NaCLO3–H2O and HCLO4–NaCl–H2O

A new model for mixtures (two and more solutes) of aqueous electrolyte solutions was found to be as accurate as other models, or more accurate, in prediction of new experimental results of the ternary systems HClO₄–NaClO₃–H₂O and HClO₄–NaCl–H₂O. The water activity values are then used to study the mechanism of the chloride–chlorate reaction, generating chlorine dioxide: 2H⁺ + ClO^?₃ + Cl^? → ClO₂ + 1/2Cl₂ + H₂O Spectrophotometric measurements of the production rate of ClO₂ have confirmed that the intermediary species in the proposed equilibrium H⁺(mH₂O) → H⁺(m-n)H₂O + nH₂O Is actually H(H₂0)⁺_m-n. The final kinetic expression for the reaction rate of chlorine dioxide generation, used in pulp bleaching, is then derived to explain the high order with respect to acid concentration.     

Separation of Uranium from Aqueous Solutions Using Al3+‐ and Fe3+‐modified Titanium‐ and Zirconium Phosphates

Abstract

The ability of four amorphous Al³⁺‐ and Fe³⁺‐doped titanium and zirconium sorbents to separate U(VI) from acidic aqueous solutions (pH_init=3, ionic strength 0.1 M established by NaNO₃) was investigated using a batch technique and instrumental neutron activation analysis. All investigated sorbents were found to be chemically stable and remove considerable amounts of uranium from acidic aqueous solutions (pH_init=3). The scanning electron microscopic and powder‐X‐ray diffraction examination of the grains of the two investigated titanium phosphates after contacting the uranium solutions revealed the formation of sodium autunite (Na₂(UO₂)₂(PO₄)₂ · 6‐8H₂O) accompanied, in the case of the Fe³⁺‐doped titanium phosphate, by iron uranyl phosphate hydroxide hydrate (Fe(UO₂)₂(PO₄)₂(OH) · 7H₂O). No crystal formation was observed in the cases of uranium sorbed by zirconium phosphates indicating the different sorption mechanism involved.     

Extraction equilibria of chromium(VI) from sulfuric acid solutions with tri-n-octylphosphine oxide

The extraction equilibria of chromium(VI) from sulfuric acid solutions with tri-n-octylphosphine oxide (TOPO) dissolved in kerosene at 25°C have been studied. The possible complexes of chromium(VI) with TOPO in organic phase and extraction constants were determined by best fitting the distribution coefficient expression of Cr(VI) with experimental data using the Rosenbrock method. The extraction reactions, including the equilibria among seven species in aqueous phase (H₂CrO₄, HCrO₄⁻, HCr₂O₇⁻, Cr₂O₇²⁻, CrSO₇²⁻, HSO₄⁻ and SO₄²⁻) and five possible complexes in organic phase (H₂CrO₄·(TOPO), H₂Cr₂O₇·(TOPO)₃, H₂CrSO₇·(TOPO)₃, H₂SO₄·(TOPO)₂ and (H₂SO₄)₂·(TOPO)₂) were proposed. The influence of initial sulfuric acid concentration on the fraction of extracted complexes and on the distribution coefficients of Cr(VI) is discussed. This result was helpful for the clarification of the extraction reactions of Cr(VI). © 1998 Society of Chemical Industry     

Kinetics of the Decolorization by Fenton's Reagent

Fenton's reagent was employed in the decolorization of aqueous solutions of one of three dyestuffs (Acid Red 27, Reactive Blue 81, Acid Blue 62). The decolorization with Fenton's reagent was found to be simple and fast. In order to determine the reaction kinetics of the decolorization the stopped-flow technique under pseudo-first order conditions was used. Experiments were carried out at pH=2, at the excess of ferrous salts (FeCl₂·4H₂O or FeSO₄·7H₂O). The rate constants of the decolorization determined by us are in the same order of magnitude: 90 to 100 dm³/(mol-s) for FeSO₄·7H₂O/H₂O₂, and 40 to 50 dm³/(mol-s) for FeCl₂·4H₂O/H₂O₂ systems. The difference between the rate constants for both ferrous salts indicates that the Fenton's reaction may proceed via different mechanisms.     

Hydrothermal synthesis and characterization of a novel two-dimensional framework materials constructed from the polyoxometalates and coordination groups: [As8IIIV14IVO42(CO3)][Cu(en)2]3·10H2O

A new compound [As₈^IIIV₁₄^IVO₄₂(CO₃)][Cu(en)₂]₃·10H₂O (1) has been synthesized from V₂O₅,As₂O₃,CuCl₂·2H₂O, en and H₂C₂O₄·2H₂O in aqueous solution using the hydrothermal method and characterized by single-crystal X-ray diffraction analysis. X-ray crystallography reveals that 1 is a novel two-dimensional framework material constructed from the mixed As/V polyoxometalates and coordination groups.     

Synthesis,structural and spectroscopic studies of 1-(2-FUROYL)-3-phenylthiourea: a theoretical and experimental approach

The thiourea derivative 1-(2-Furoyl)-3-phenylthiourea (FPT) was synthesized and characterized by using spectroscopic (IR, Raman, UV–VIS, ¹H and ¹³C NMR) and structural methods (powder X-ray diffraction data). The experimental measurements were complemented with quantum chemical calculations. FPT crystallizes in the monoclinic crystal system, space group P21/c, with cell parameters a?=?4.7679(5) Å, b?=?20.9704(2) Å, c?=?12.5109(5) Å and β?=?109.811(10)°, V?=?1176.87(3) ų. In the crystal structure, the thiourea group makes dihedral angle of 43.8(5)° with the furoyl group, whereas the benzene ring is inclined by 24.3(4)°. The anti-syn geometry of the thiourea unit is stabilized by intramolecular N–H^?…?O hydrogen bond between the H atom of the syn thioamide and the carbonyl O atom. In the crystal structure, molecules of FPT are packed through N–H···S, C–H···O and C–H···C hydrogen bonds, and a π–π interaction with offset arrangement. Hirshfeld surface analysis was performed in order to evaluate and quantify intermolecular interactions. The Hirshfeld surface analysis indicated that the H···H interactions comprise the majority of interactions. Shape index and curvedness clearly indicate π–π interactions in the compound FPT.     

Antimony Solubility and Speciation in Aqueous Sulphuric Acid Solutions at 298 K

This work is an experimental and theoretical study of antimony speciation and the solubility of Sb₂O₅, Sb₂O₃ and Sb₂(SO₄)₃ at 298 K in aqueous sulphuric acid solutions (0 to 6 kmol/m³). A thermodynamic model was developed to quantify the solubility products and aqueous metal speciation. Main dissolved species were H₃SbO_3(aq) and H₃SbO_4(aq). The solubility of antimony increases with increasing solution acidity and with the presence of hydrogen peroxide in the solution. The following standard equilibrium constants at 298 K were obtained: Log K⁰_(Sb2O5) = 11.7±0.5, Log K⁰_(Sb2O3) = 32±1, and Log K⁰_(Sb2(SO4)3) = 55±2.     

A New Metal–Organic ZnII Supramolecular Assembled via Hydrogen Bonds and N···N Interactions as a New Precursor for Preparation Zinc(II) Oxide Nanoparticles, Thermal, Spectroscopic and Structural Studies

A new 1D supramolecular involving two different ligands, {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O (GB = 2-guanidinobenzimidazole and bpe = 1,2-bis(4-pyridyl)ethylene, has been synthesised, characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy. The thermal stability of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O was studied by thermal gravimetric and differential thermal analyses. The single crystal X-ray analysis shows that the complex is a one-dimensional polymer involving macrocycle rings as a result of non-covalent bridging bpe ligands via N–H···N and N···N interactions, N–H···bpe···bpe···H–N, with the basic repeating {[Zn(GB)₂](μ-bpe)₃}(ClO₄)₂·H₂O units and by connecting [Zn(GB)₂]²⁺ nodes. ZnO nanoparticles were obtained by calcination of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O at 500 °C in air. The nanoparticles were characterized by X-ray diffraction and scanning electron microscopy.     

Catalytic deNO x properties of novel vanadium oxide based open-framework materials

The deNO _x catalytic properties of a new class of open-framework structure materials, Li₆[Mn₃(H₂O)₁₂V₁₈O₄₂(XO₄)] · 24H₂O (X = V, S) (1), [Fe₃(H₂O)₁₂ V₁₈O₄₂(XO₄)] · 24H₂O (X = V, S) (2), [Co₃(H₂O)₁₂V₁₈O₄₂(XO₄)] · 24H₂O (X = V, S) (3), and Li₆[Ni ₃ ^II (H₂O)₁₂V ₁₆ ^VI V ₂ ^V O₄₂(SO₄)] · 24H₂O (4), have been studied. The crystal structures of these novel systems consist of three-dimensional arrays of vanadium oxide clusters {V₁₈O₄₂(XO₄)} , as building block units, interlinked by {–O–M–O–} (M = Mn, 1; M = Fe, 2; M = Co, 3; M = Ni, 4) bridges. Their open-framework structures contain cavities, similar to those observed in conventional zeolites, which are occupied by exchangeable cations and/or readily removable water of hydration. The catalysts derived from these materials were tested for the selective catalytic reduction (SCR) of nitrogen oxides {NO _x } into N₂ using a hydrocarbon, propylene, as the reducing agent. The catalysts were ineffective under lean burn conditions. However, the new catalysts, especially the one derived from the cobalt derivative (3), showed intriguing deNO _x activity under rich conditions. They remove up to ~ 99% of the toxic NO _x emissions in 1.5% O₂ with 100% selectivity to N₂. The active phase of the catalysts exhibit good stability, can be readily regenerated, and are selective to the desired product-N₂. The catalytic reactions occur at moderately low temperatures (400–500 °C). The catalysts were characterized by FT-IR, temperature programmed reactions (TPR and TPO), SEM, BET surface area measurements, elemental analysis, and X-ray diffraction (XRD). Additional advanced techniques were used to further characterize the catalyst phases that showed most promising deNO _x activity and increased tolerance to oxygen.     

A puckered 2D copper coordination polymer with dimensions 14.91×12.63 Å

The polymeric complex [Cu(spcp)₂(H₂O)]_n·(H₂O)_2n (spcp⁻=4-sulfanylmethyl-3-phenylcarboxylate pyridine) with puckered grids of dimensions 14.91×12.63 Å was obtained in the reaction of the Cu(OAc)₂·5H₂O with Na(spcp) by solvothermal method.     

Formation of Mixed Bond‐Angle Linkages in Zinc Boromolybdate Glasses

The short and medium range structure of glassy MoO₃–ZnO–B₂O₃ has been studied by neutron diffraction and reverse Monte Carlo simulation. The partial atomic pair correlation functions and coordination numbers are presented that are not yet reported for this system. We have established that the first neighbor distances do not depend on concentration within limit of error, the actual values are r_B‐O = 1.38 Å, r_Mo‐O = 1.72 Å, and r_Zn‐O = 1.97 Å. It is found that ZnO takes part in the glassy structure as network former, as ZnO₄ tetrahedral are linked both to MoO₄ and to BO₃ and BO₄ groups. It is revealed that BO₄/BO₃ increases with increasing B₂O₃ content. We have found that only small amount of boroxol ring is present, BO₃ and BO₄ groups are organized into superstructure units, and a small part is in isolated BO₃ triangles. The BO₃ and BO₄ units are linked to MoO₄ or ZnO₄ forming mixed ^[4]Mo‐O‐^[3]B, ^[4]Mo‐O‐^[4]B, ^[4]Mo‐O‐^[4]Zn, ^[3]B‐O‐^[4]Zn, ^[4]B‐O‐^[4]Zn bond linkages.     

A novel dimer of oxo-di(acetato)-bridged manganese(III) dimers complex of potential biological significance

Assembly of the tetranuclear oxomanganese(III) acetato cluster [Mn₄O₂(O₂CMe)₇(phen)₂](BF₄) from the dinuclear oxo-di(acetato)-bridged manganese(III) species [Mn₂O(O₂CMe)₂(H₂O)₂(phen)₂](BF₄)₂·3H₂O in aqueous/acetic acid MeOH solution occurs via the new ‘dimer of dimers’ Mn^III complex [Mn₂O(O₂CMe)₃(H₂O)(phen)₂](BF₄)·MeOH possesing an unprecedent [Mn₄(μ-O)₂(μ-O₂CMe)₄(μ-OH₂^…O₂CMe)₂] core.     

A novel two-dimensional network self-assembled by the narrowest ladder cations [Cu(CH3COO)(bpe)(H2O)]nn+ containing the Cu2(μ-O)2 cores and the dimeric anions [Cu2(nta)2(bpe)]2− through hydrogen-bonding interaction

A novel complex [Cu(CH₃COO)(bpe)(H₂O)]_n·n/2[Cu₂(nta)₂(bpe)] ·6nH₂O) (bpe=trans-1,2-bis(4-pyridyl)ethylene) was synthesized and characterized. The molecule structure shows that it is composed of the ladder-like double chain cations [Cu(CH₃COO)(bpe)(H₂O)]_nⁿ⁺ and the dimeric anions [Cu₂(nta)₂(bpe)]²⁻. Through bridging oxygen atom of the acetate, the Cu₂ (μ-O)₂ core is formed. The ladder-like chain cation is the narrowest ladder [3.422(3) Å]. Two-dimensional undulating network is constructed by the cations and the dimeric anions through hydrogen-bonding interactions.