Dithiacrown Ether Substituted Porphyrazines: Synthesis, Single-Crystal Structure, and Control of Aggregation in Solution by Complexation of Transition-Metal Ions

The synthesis of novel magnesium, copper, and metal-free porphyrazines, peripherally substituted with dithia-7-crown-2 (MPz(7)), dithia-15-crown-5 (MPz(15)), and dithia-18-crown-6 (MPz(18)) macrocycles is reported. These compounds are prepared starting from dicyanoethylene containing crown ethers 3, 2(1), and 2(2), respectively, which contain sulfur as well as oxygen heteroatoms. The "crowned" porphyrazines bind silver(I) and mercury(II) perchlorates. UV/vis spectroscopy and electron paramagnetic resonance measurements reveal that addition of the transition-metal ions leads to dimerization of the porphyrazine complexes. In the case of the dithia-18-crown-6-substituted porphyrazines, the dimers break up to form monomeric 6:1 guest-host complexes when more than 2 equiv of the metal ion is added. The single-crystal structures of the crown ether 2(2) and the porphyrazine MgPz(18) are presented. Compound C(14)H(20)N(2)O(4)S(2) (2(2)) crystallizes in the monoclinic space group P2(1)/c with a = 10.9310(13) ?, b = 19.383(3) ?, c = 8.6976(14) ?, beta = 108.898(11) degrees, V = 1743.5(5) ?(3), and Z = 4. The structure refinement converged to R = 0.0366 and R(w) = 0.0504. Compound C(56)H(82)MgN(8)O(17)S(8) (MgPz(18)) crystallizes in the triclinic space group P&onemacr; with a = 9.584(3) ?, b = 17.672(2) ?, c = 19.620(4) ?, alpha = 84.904(14) degrees, beta = 85.21(2) degrees, gamma = 89.29(2) degrees, V = 3298.4(13) ?(3), and Z = 2. The structure refinement converged to R1 = 0.0839 and wR2 = 0.2196. The electrical properties of H(2)Pz(18) have been studied by complex impedance spectroscopy. The bulk electrical conductivity of this compound is approximately 1 order of magnitude higher than that of the corresponding 18-crown-6 phthalocyanine.     

Über eine universelle Ultramikrobestimmung des Schwefels in organischen Substanzen. I

Zusammenfassung Eine Methode zur Bestimmung von Schwefelmengen bis zu 20g in organischen Substanzen wird beschrieben. Das Verfahren ermöglicht die bei Mikroverfahren übliche Analysengenauigkeit.Der durch Reduktion mittels Sn(II)-Phosphat in konz. Phosphorsäure gebildete Schwefelwasserstoff wird mit Natronlauge in einer Cd(II)-Sulfatlösung titriert. Phosphor, Stickstoff, Halogene und die meisten Metalle stören nicht. Eine Blindwertkorrektur ist notwendig. Einige Berechnungen erläutern die Methode.

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Summary A method is described for determining amounts of sulfur up to 20g in organic substances. The precision that is usual in the analyses by the micromethods can be expected from this procedure. The hydrogen sulfide produced by reduction with Sn(II) phosphate in conc. phosphoric acid is titrated with sodium hydroxide in a Cd(II)-sulfate solution. Phosphorus, nitrogen, halogens and most metals do not interfere. A blank value correction is essential. The method is illustrated by several calculations.

     

Quantum-chemical study of the interface formed by carboxylic species on TiO<Subscript>2</Subscript> nanoparticles. 1. Nanoparticle surface

The current paper presents results of a quantum-chemical study of the surface structure of nanoparticles of both rutile and anatase crystallographic modifications. Different stages of the surface relaxation are discussed. Water adsorption is considered. The calculations were performed in the spd-basis by using semi-empirical quantum-chemical codes, both sequential and parallel. The results are mainly addressed to the study of the interface formed by titania nanoparticles and a set of carboxylated species, namely, benzoic, bi-isonicotinic acids as well as tris-(2,2′-dcbipyridine) Fe(II) complex placed on the surface of either rutile or anatase polymorphs.This revised version was published online in August 2005 with a corrected issue number.     

Structure and properties of thin-film metal-poly(p-xylylene) hybrid nanocomposites

Thin-film hybrid metal-poly(p-xylylene) composites synthesized by vacuum co-condensation were examined. It was demonstrated that the structure of the composites consists of a matrix comprised of polymer globules and inorganic filler nanoparticles. The shape, structure, and size of the polymer globules depend on the film thickness and the nature of the filler nanoparticles. Studying the conductivity of these materials demonstrated that it is determined by hopping conduction via surface states of the matrix. At high frequencies of the voltage applied (above 500 Hz), the electric conduction characteristics depend appreciably on the processes of recharging of the surface states of the matrix and of the nanoparticle-matrix interfaces. Tests of lithium battery anodes prepared from nanocomposites showed that these materials are promising for manufacturing chemical current sources.     

Third Joint ESF–NSF Symposium on ‘Nanoparticles: Applications in Materials Science and Environmental Science and Engineering,’ Dublin,Ireland, September 6, 2000

Journal of Nanoparticle Research -     

Photocatalytically-assisted electrochemical degradation of <Emphasis Type="Italic">p</Emphasis>-aminophenol in aqueous solutions using zeolite-supported TiO<Subscript>2</Subscript> catalyst

This paper reports the results of an investigation into enhancement of the electrochemical oxidation of p-aminophenol (4-AP) in an aqueous solution with a boron-doped diamond (BDD) electrode, assisted by photocatalysis using a zeolite-supported TiO₂ (Z-TiO₂) catalyst. The BDD electrode was characterised in 0.1 M Na₂SO₄-supporting electrolyte and the presence of 4-AP by open-circuit potential behaviour (OCP) and cyclic voltammetry (CV). The electrode behaviour was investigated in the dark and following UV irradiation and in the absence/presence of the Z-TiO₂ catalyst. The electro-oxidation process was carried out using chronoamperometry (CA) and multiple-pulsed amperometry (MPA) at the selected potential under potentiostatic conditions. The electrochemical degradation process of 4-AP on the BDD electrode was improved by the application of a pulsed potential, which allowed both in-situ electrochemical cleaning of the electrode and indirect oxidation of 4-AP by oxygen evolution. The application of photocatalysis using Z-TiO₂ in the 4-AP electrochemical degradation exhibited an enhanced effect when the anodic potential was set at +1.25 V vs. Ag/AgCl in the water stability region, close to the oxygen evolution potential.     

Effect of a rhombohedral phase on lithium intercalation capacity in graphite

Five natural graphites with different rhombohedral phase (3R phase) content have been investigated as anode materials for rechargeable lithium-ion batteries. The reversible capacity varies from 250 mA h/g to 350 mA h/g for the same intercalation conditions depending on the content of the 3R-phase. With increasing rhombohedral phase in the graphite, the intercalation capacity will be high. A peak at about 10 mV in the cyclic voltammograms (CV) of a sample with a large 3R-phase content is caused by lithium ions occupying boundaries between the rhombohedral (3R) phase and the hexagonal (2H) phase and is responsible for a capacity exceeding the theoretical value.     

Electronic conductivity in La1−xBaxF3−x crystals

The electronic conductivities of solid solutions La_1?xBa_xF_3?x (0 ? x ? 0.0952) were investigated up to 533 K using the Hebb-Wagner dc polarization technique. The electrochemical cell (-)La|La_1?xBa_xF_3?x|Pt(+) has been utilized with Pt as the ion-blocking electrode. Under steady-state conditions the La_1?xBa_xF_3?x solid solutions exhibit electronic conductivity. The electronic conductivity vanishes in pure LaF₃. Together with ac conductivity measurements it appears that the ionic transference number for La_1?xBa_xF_3?x (0 ? x ? 0.0952) is essentially unity over the temperature range studied.     

Ionic conductivity in tysonite-type solid solutions La1−xBaxF3−x

The ionic conductivity of single crystals of tysonite-type solid solutions La_1?xBa_xF_3?x(0?x?0.095) has been studied parallel and perpendicular to the crystallographic c axis in the temperature range 293–1300 K. Three regions can be discerned in the compositional dependence of the ionic conductivity: (i) the “pure” crystal, in which at room temperature no exchange occurs between different types of anion sites in the tysonite structure; (ii) an intermediate region(0 < x < 7 × 10^-2) which reveals changes in both the conductivity activation enthalpy and the magnitude of the conductivity; (iii) a concentrated solid-solution region (x > 7 × 10^-2), where fluoride ions interchange easily among the different anion sublattices. Diffusion coefficients calculated from ionic conductivity results, are in good agreement with those calculated from ¹⁹F NMR measurements. Using the present data, along with ¹⁹F NMR data, dielectric relaxation data and structural considerations, mechanisms governing the ionic conductivity are proposed.     

Hole conduction in pure and doped lead bromide crystals

The conductivity of pure and doped lead bromide was measured in a bromine atmosphere in the temperature region 25–200°C. The defect chemistry of nonstoichiometric lead bromide is presented. The hole mobility was derived from the time dependent change in the conductivity after admission/removal of the bromine ambient. Preliminary evidence is presented for hole trapping at Fe²⁺ and Cu⁺ centres in lead bromide.