Synthesis and structural characterization of Zn(O3PCH2OH), a new microporous zinc phosphonate

Zn(O3PCH2OH) (1) has been formed by reaction of zinc acetate with diethyl hydroxymethylphosphonate. The acidity of the zinc solution effects hydrolysis of the phosphonate to produce phosphonic acid in situ. 1 crystallizes in the trigonal spacegroup R3, with a = 15.9701(2) A, c = 7.783(2) A, and Z = 18. The compound has channels in the [001] direction, formed by phosphonate groups bridging the octahedral coordinated zinc atoms. The zinc atoms are coordinated by the three oxygens of the phosphonate group and the oxygen of the hydroxy group.     

Zn[BPO4(OH)2]: a zinc borophosphate with the rare moganite-type topology

A novel zinc borophosphate Zn[BPO(4)(OH)(2)] with moganite-type topology (a rare polymorph of silica) has been prepared from a mixture of ZnO, B(2)O(3), and P(2)O(5) by hydrothermal treatment at 443 K. The crystal structure was determined from single-crystal X-ray data (orthorhombic, Pbcn (no. 60), a=915.07(3), b=897.22(3), c=1059.19(3) pm, V=869.62(5)x10(6) pm(3), Z=8, R1=0.028, wR2=0.075). The crystal structure comprises unbranched vierer-single borophosphate chains running along [010] and interconnected via ZnO(2)(OH)(2)-tetrahedra by sharing common vertices. The resulting topology of the three-dimensional tetrahedral framework structure is described by the Schl?fli symbol (4(2).6(2).8(2))(4.6(4).8)(2). Although showing Zn in a tetrahedral coordination, the title compound does not belong to the group of zincoborophosphates but is a special case of a borophosphate containing vierer single rings of tetrahedra with the sequence Zn-B-Zn-P.     

Thermal dehydration kinetics of a rare earth hydroxide,Gd(OH)3

This paper reports the synthesis, characterization, and dehydration kinetics of a rare earth hydroxide, Gd(OH)₃. Uniform rod‐like Gd(OH)₃ powder was prepared by a colloidal hydrothermal method. The powder thus obtained dehydrated into its oxide form in a two‐step process, where crystalline GdOOH was obtained as the intermediate phase. Crystal structure study revealed a monoclinic structure for GdOOH, with space group P2/1m and lattice parameters a = 6.0633, b = 3.7107, c = 4.3266, and β = 108.669. The first‐step dehydration follows the F2 mechanism, while the second step follows the F1 model, indicating that both the steps are controlled by nucleation/growth mechanism. The activation energy E_a and frequency factor A are 231±12 kJ/mol and 2.08 × 1018 s^?1 for the first step and 496 ± 32 kJ/mol and 7.88 × 10³³ s^?1 for the second step, respectively. Such high activation energy calculated from the experimental data can be ascribed to the high bonding energy of Gd? O bond, and the difference in activation energy for the two steps is due to the change in the bond length of hexagonal Gd(OH)₃ and monoclinic GdOOH. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 75–81, 2007     

Synthesis and structure of a novel supramolecular Zn3Co8 assembly containing a linear Zn3 core

Reaction of Zn(OAc)(2).2H2O (OAc = acetate) with LH2 in THF followed by reaction with Co2(CO)8 yields the novel supramolecular assembly Zn3L2(OAc)2[Co2(CO)6](4).0.5CH2Cl2, which was characterized by X-ray diffraction (LH2 = (CH2)3(N=CH-2-OH-5-C identical to CSiMe3C6H3)2 or N,N'-propylenebis(2-hydroxy-5-trimethylsilylethynl-1-aldimine).     

Chemical modification of zinc hydroxide nitrate and Zn-Al-layered double hydroxide with dicarboxylic acids

A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2.2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate ((-)OOC(CH2)4COO(-)), azelate ((-)OOC(CH2)7COO(-)), and benzoate (C6H5COO(-)) ions through ion exchange reactions. Solid state 13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratio g ||/A ||=170 cm and, after intercalation of adipate, the change was not significant: g ||/A ||=174 cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio to g ||/A ||=194 cm, similar to the spectra of ZHN modified with adipate, g ||/A ||=199 cm, and azelate, g ||/A ||=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.     

Interaction of Mg3Si2O5(OH)4 nanotubes with potassium hydroxide

Interaction of Mg₃Si₂O₅(OH)₄ nanotubes with aqueous solutions of potassium hydroxide in various temperature-time treatment modes was studied.     

Esr spin trapping evidence for SO.- 3 and .OH radicals in sulfite oxidation

Electron spin resonanee (ESR) spin trapping experimenss have been carried out to investigate the mechanism of sulfite oxidation employing 5,5-dimethyl-1-pyrroine-1-oxide (DMPO) as a spin trap. The results show that sulfite autoxidation, catalyzed by Mn(II), involves not only the SO^.- ₃ radicals but also the .OH radicals. An addition of H₂O₂ to the sulfite aqueous medium significantly increases the .OH radical formation. This result provides new clues to the chemical mechanism of the sulfite oxidation and the sulfite toxicity.     

Sodium cobalt aminomethylidenediphosphonate with a novel open framework structure

This paper reports the synthesis and crystal structure of a cobalt aminomethylenediphosphonate compound NaCo(2)[NH(3)CH(PO(3))(PO(3)H(0.5))](2)(H(2)O)(2).xH(2)O (1). It shows a novel open framework structure in which layers of Co(2)[NH(3)CH(PO(3))(PO(3)H(0.5))](2)(H(2)O)(2) are connected by NaO(6) linkages. The magnetic studies show a dominant antiferromagnetic exchange between the Co(II) ions.     

2D calculation of anharmonic OH vibrations in a layered hydroxide crystal

Anharmonic vibrational frequencies for the Raman-active (A(1g)) and the IR-active (A(2u)) modes have been calculated for the LiOH crystal within a plane-wave density functional theory (DFT) framework. We find that a two-dimensional quantum-mechanical vibrational approach, allowing for anharmonic coupling between symmetric and antisymmetric OH stretching modes, produces OH frequencies--both absolute frequencies and gas-to-solid frequency shifts--in good agreement with experiment. Remaining errors in the absolute frequencies are largely a consequence of the DFT model chosen. A one-dimensional normal-mode following vibrational treatment, on the other hand, fails to reproduce both absolute anharmonic frequencies and gas-to-solid frequency shifts.     

Synthesis and anion exchange properties of a Zn/Ni double hydroxide salt with a guarinoite structure

In this study, the first route to synthesize a compound with the guarinoite structure (Zn,Co,Ni)₆(SO₄)(OH,Cl)₁₀·5H₂O is reported. Zn/Ni guarinoite is obtained from the reaction of NiSO₄·7H₂O with solid ZnO in aqueous solution. The resulting green Zn/Ni guarinoite ((Zn_3.52Ni_1.63)(SO₄)_1.33(OH_7.64)·4.67H₂O) was characterized by X-ray diffraction, infrared spectrometry, UV–Visible spectrometry and thermal analysis. It is shown that its structure is similar to the one described for the layered Zn sulfate hydroxide hydrate, i.e. brucite layers with empty octahedra presenting tetrahedrally coordinated divalent atoms above and below the empty octahedra. Ni atoms are located in the octahedra and zinc atoms in tetrahedra and octahedra. In this structure the exchangeable anions are located at the apex of tetrahedra. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that the Zn/Ni guarinoite is composed of aggregates of hexagonal plates of several hundreds of nanometers. Due to its interest for industrial or environmental applications, the exchange of sulfate groups by carbonates has been investigated. Results show a limited exchange and a higher affinity of the Zn/Ni guarinoite for sulfates compared to carbonates.     

Combining valproate and bipyridyl ligands to construct a 0D core‐shell Zn5(μ3‐OH)2 cluster and a 2D layered coordination network with a [Zn3(μ3‐OH)]2 SBU

Starting from the proposed zinc carboxylate cluster tetrakis(μ‐2‐propylpentanoato)dizinc(II), Zn₂(μ₂‐valp)₄ ( I ), of valproic acid, a branched short‐chain fatty acid, and bipyridine ligands, two new mixed‐ligand coordination compounds, namely, bis(2,2′‐bipyridine)di‐μ₃‐hydroxido‐hexakis(μ‐2‐propylpentanoato)bis(2‐propylpentanoato)pentazinc(II), [Zn₅(C₈H₁₅O₂)₈(OH)₂(C₁₀H₈N₂)₂] ( II ), and poly[[bis(μ‐4,4′‐bipyridine)di‐μ₃‐hydroxido‐octakis(μ‐2‐propylpentanoato)bis(2‐propylpentanoato)hexazinc(II)] dimethylformamide disolvate], {[Zn₆(C₈H₁₅O₂)₁₀(OH)₂(C₁₀H₈N₂)₂]·2C₃H₇NO}_n ( III ), were synthesized. Compound II is a core‐shell‐type zero‐dimensional discrete Zn₅(μ₃‐OH)₂ metal–organic cluster with Zn ions in double‐triangle arrangements that share one Zn ion coincident with an inversion centre. The cluster contains three crystallographically non‐equivalent Zn ions exhibiting three different coordination geometries (tetrahedral, square pyramidal and octahedral). The cluster cores are well separated and embedded in a protective shell of the aliphatic branched short chains of valproate. As a result, there is no specific interaction between the discrete clusters. Conversely, compound III , a 2D layered coordination network with a secondary building unit (SBU), is formed by Zn₆(μ₃‐OH)₂ clusters exhibiting a chair‐like hexagonal arrangement. This SBU is formed from two Zn₃(μ₃‐OH) trimers related by inversion symmetry and connected by two syn–anti bridging carboxylate groups. Each SBU is connected by four 4,4′‐bipyridine ligands producing a 6³‐hcb net topology. 2D coordination layers are sandwiched within layers of dimethylformamide molecules that do not interact strongly with the network due to the hydrophobic protection provided by the valproate ligands.     

Amperometric determination of sulfite with sulfite oxidase immobilized at a platinum electrode surface

Sulfite oxidase is immobilized on collagen membrane at the surface of a platinum electrode and catalyzes the oxidation of sulfite to sulfate with stoichiometric production of hydrogen peroxide. The hydrogen peroxide is detected amperometically at the platinum electrode at an applied potential of 700 mV. The system responds linearly to sulfite in the range 1–150 μM, with a detection limit of 0.2 μM. The enzyme retains over 95% of its activity for three weeks if stored at ?20° C when the probe is not in use.     

Electrocatalytic sulfite biosensor with human sulfite oxidase co-immobilized with cytochrome c in a polyelectrolyte-containing multilayer

An efficient electrocatalytic biosensor for sulfite detection was developed by co-immobilizing sulfite oxidase and cytochrome c with polyaniline sulfonic acid in a layer-by-layer assembly. QCM, UV–Vis spectroscopy and cyclic voltammetry revealed increasing loading of electrochemically active protein with the formation of multilayers. The sensor operates reagentless at low working potential. A catalytic oxidation current was detected in the presence of sulfite at the modified gold electrode, polarized at +0.1 V (vs. Ag/AgCl 1 M KCl). The stability of the biosensor performance was characterized and optimized. A 17-bilayer electrode has a linear range between 1 and 60 μM sulfite with a sensitivity of 2.19 mA M⁻¹ sulfite and a response time of 2 min. The electrode retained a stable response for 3 days with a serial reproducibility of 3.8% and lost 20% of sensitivity after 5 days of operation. It is possible to store the sensor in a dry state for more than 2 months. The multilayer electrode was used for determination of sulfite in unspiked and spiked samples of red and white wine. The recovery and the specificity of the signals were evaluated for each sample. Figure Schematic of the bioelectrocatalytic sulfite sensor: sulfite oxidase (green) oxidizes sulfite to sulfate and transfers electrons via heme b ₅ to cyt c (red) and thence to the gold electrode     

New framework connectivity patterns in templated networks: the creatinine zinc phosphites C4N3OH7.ZnHPO3, C4N3OH7.Zn(H2O)HPO3, and (C4N3OH7)2.ZnHPO3.H2O

The syntheses, crystal structures, and properties of C(4)N(3)OH(7).ZnHPO(3), C(4)N(3)OH(7).Zn(H(2)O)HPO(3), and (C(4)N(3)OH(7))(2).ZnHPO(3).H(2)O are reported. These new creatinine zinc phosphites are built up from networks of vertex-sharing HPO(3) pseudopyramids and various types of ZnO(2)N(2), ZnO(3)N, and ZnO(2)N(H(2)O) tetrahedra, resulting in extended structures of different dimensionalities (as sheets, clusters, and chains, respectively). They demonstrate the structural effect of incorporating "terminal" (nonnetworking) Zn-N and Zn-OH(2) moieties into zinc centers. Crystal data: C(4)N(3)OH(7).ZnHPO(3), triclinic, P1 (No. 2), a = 8.9351(4) A, b = 9.5011(4) A, c = 9.9806(4) A, alpha = 87.451(1) degrees, beta = 85.686(1) degrees, gamma = 89.551(1) degrees, Z = 4; C(4)N(3)OH(7).Zn(H(2)O)HPO(3), monoclinic, P2(1)/c (No. 14), a = 10.1198(7) A, b = 7.2996(5) A, c = 13.7421(9) A, beta = 107.522(1) degrees, Z = 4; (C(4)N(3)OH(7))(2).ZnHPO(3).H(2)O, triclinic, P1 (No. 2), a = 10.7289(6) A, b = 10.9051(6)A, c = 13.9881(8) A, alpha = 89.508(1) degrees, beta = 74.995(1) degrees, gamma = 74.932(1) degrees, Z = 4.