The role of anions in oxygen reduction in neutral and basic media on gold single-crystal electrodes

Oxygen reduction on well-defined single-crystal electrodes in different basic and neutral media has been studied using the impinging jet system. The results obtained with this system in 0.1 M NaOH are comparable to those reported in the literature for rotating disk electrodes, indicating that the impinging jet system behaves as a system in which the thickness of the diffusion layer is stationary. The activity of the Au(100) electrode is considerably higher than the rest of the basal planes in all media and yields water when E>–0.2 V and hydrogen peroxide for E<–0.2 V on the SHE scale. For Au(111) and Au(110) the activity of the electrode is much smaller and the final product is always hydrogen peroxide. The transition between both mechanisms for the Au(100) is, essentially, independent of the solution pH. In acid media the final product is always hydrogen peroxide for all the electrodes studied. The differences between the activities of the electrodes have been explained in the light of the different adsorption properties of the surfaces in relation to HO₂ ^–. In the case of the Au(100) electrode, the existence of a negative charge density on the metal inhibits further reduction of HO₂ ^–.Dedicated to Prof. Dr. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry     

A new ternary cadmium–zirconium–sodium oxalate with an open framework: crystal structure, solid-state NMR spectroscopy and thermal behavior

A mixed cadmium-zirconium-sodium oxalate with an open architecture has been synthesized from precipitation methods at ambient pressure. It crystallizes in an hexagonal system, space group P6₄22 (no. 181), a=8.793(1)Å, c=24.530(1)Å, V=1642.5(3)ų and Z=3. The structure displays a [CdZr(C₂O₄)₄]²⁻ helicoidal framework. It is built from CdO₈ and ZrO₈ square-based antiprisms connected through bichelating oxalates and displays channels along different directions. The sodium counter-cations are located inside the voids of the structure together with water molecules. They exhibit a dynamic disorder which has been further investigated by ¹H and ²³Na solid-state NMR. The study pointed out two types of water molecules and sodium atoms, with a high mobility for one of each. The thermal decomposition has been studied in situ by temperature-dependent X-ray diffraction and thermogravimety. The final product is a mixture of cadmium oxide, zirconium oxide and amorphous sodium carbonate.     

Contrasting oxide crystal chemistry of Nb and Ta:: The structures of the hexagonal bronzes BaTa2O6 and Ba0.93Nb2.03O6

The high-temperature hexagonal forms of BaTa₂O₆ and Ba_0.93Nb_2.03O₆ have P6/mmm symmetry with unit-cell parameters a=21.116(1) Å, c=3.9157(2) Å and a=21.0174(3) Å, c=3.9732(1) Å, respectively. Single crystal X-ray structure refinements for both phases are generally consistent with a previously proposed model, except for displacements of some Ba atoms from high-symmetry positions. The structures are based on a framework of corner- and edge-connected Nb/Ta-centred octahedra, with barium atoms occupying sites in four different types of [0 0 1] channels with hexagonal, triangular, rectangular and pentagonal cross-sections. The refinements showed that the non-stoichiometry in the niobate phase is due to barium atom vacancies in the pentagonal channels and to extra niobium atoms occupying interstitial sites with tri-capped trigonal prismatic coordination. The origin of the non-stoichiometry is attributed to minimisation of non-bonded Ba-Ba repulsions. The hexagonal structure is related to the structures of the low-temperature forms of BaNb₂O₆ and BaTa₂O₆, through a 30° rotation of the hexagonal rings of octahedra centred at the origin.     

Polyhedral monocarbaborane chemistry : Reactions of the [6-Ph-nido-6-CB9H11] anion with two-electron donors to yield a series of neutral arachno and closo ten-vertex monocarbaborane derivatives

Reaction of the ten-vertex [6-Ph-nido-6-CB₉H₁₁]⁻ anion (1) with two-electron donor ligands L, where L is SMe₂, NH₂Ph, NC₅H₅, NC₅H₄-para-CH₂Ph, NC₅H₄-para-Ph or NC₉H₇ (where NC₉H₇ is quinoline) in the presence of {FeCl₃(OH₂)₆} gives the six neutral arachno ten-vertex monocarbaboranes [6-Ph-9-L-arachno-6-CB₉H₁₂], compounds 2, 3, 4, 7, 9 and 11, respectively, isolatable in yields of up to 63%. On prolonged treatment with {FeCl₃(OH₂)₆} oxidative cluster closure of the four compounds 4, 7, 9 and 11 that have pyridine-type ligands gives the neutral closo ten-vertex monocarbaboranes [1-Ph-6-L-closo-1-CB₉H₈], compounds 6, 8, 10 and 12, respectively, in yields of 49-92%. All new species 2, 3, 4, 6, 7, 8, 9, 10, 11 and 12 are characterised by single-crystal X-ray diffraction analysis and NMR spectroscopy. [This paper is an annotated exposition of parts of an oral presentation at the Third Pan-European Meeting of Boron Chemists, EUROBORON-3, Pruhonice, The Czech Republic, September 2004, of which the proceedings constitute this volume of Journal of Organometallic Chemistry.]     

N-H?S hydrogen bonding in 2-mercapto-5-methyl-1,3,4-thiadiazole. Synthesis and crystal structures of mercapto functionalised 1,3,4-thiadiazoles

The synthesis and crystal structures of three mercapto functionalised 1,3,4-thiadiazoles and the crystal structure of 2-mercapto-5-methyl-1,3,4-thiadiazole are described. In the solid state, 2-mercapto-5-methyl-1,3,4-thiadiazole 1 forms a thioamide tautomer as shown by FTIR and Raman spectroscopy as well as X-ray crystallography and as theoretically predicted. The molecules are connected to form chains via N-H?S hydrogen bonds with N?S=328.3 pm. Bis(2-methyl-1,3,4-thiadiazolyl)-5,5′-disulfide 2, the disulfide of 1, as well as 2-(tert-butyldithio)-5-methyl-1,3,4-thiadiazole 3 and 2,5-bis(tert-butyldithio)-1,3,4-thiadiazole 4 have been synthesised and characterised by vibrational spectroscopy and X-ray diffraction.     

Hydrothermal preparation,structure and characterizations of noncentrosymmetric LiZnO(IO3)

A new lithium zinc iodate, LiZnO(IO₃), has been prepared by hydrothermal reactions at 200 °C. Single-crystal X-ray diffraction experiment revealed that the compound crystallizes in a noncentrosymmetric orthorhombic space group Ama2 with cell parameters: a = 6.3386(6) Å, b = 11.2613(11) Å, c = 4.6840(5) Å, Z = 4. In the structure, the basic building units are the distorted ZnO₆ octahedron, LiO₄ tetrahedron and the IO₃ group. These groups are linked together to form a three-dimensional structure by sharing the oxygen atoms. The DSC measurement demonstrates that the compound is stable up to 490 °C. Powder second-harmonic generation (SHG) test shows that the SHG effect is about 2 × KH₂PO₄.     

Syntheses and characterizations of zinc(II) and copper(II) complexes with reduced Schiff base derived from salicylaldehyde and D,L-selenomethionine

New zinc(II) and copper(II) complexes with a reduced Schiff-base ligand derived from D,L-selenomethionine and salicylaldehyde have been synthesized and characterized by elemental analysis, magnetic susceptibility, IR, and NMR measurements. The single-crystal X-ray structure of the Cu(II) complex reveals that this complex is a carboxylate-bridged dimer of dinuclear copper(II) subunits and all metal centers are five-coordinate with O₄N donor sets in distorted square-pyramidal geometries. The Cu(II) complex consists of a 1-D coordination polymer.     

Supramolecular organotin(IV) dithiocarboxylates as potential antimicrobial agents

A series of tri-, chlorodi-, and diorganotin(IV) derivatives of 4-(2-methoxyphenyl)piperazine-1-carbodithioate (L) {R?=?n-C₄H₉ (1), C₆H₁₁ (2), CH₃ (3) and C₆H₅ (4)}, (n-C₄H₉)₂SnClL (5) and R₂SnL₂ {R?=?n-C₄H₉ (6), C₂H₅ (7), CH₃ (8)} have been synthesized by refluxing organotin(IV) chlorides with the ligand-salt in the appropriate molar ratio. Elemental analysis, Raman, IR, multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn), mass spectroscopic, and single-crystal X-ray crystallographic studies were undertaken to elucidate the structures of the new compounds both in solution and in the solid state. The X-ray diffraction work reveals supramolecular structures for 4 and 6, with distorted trigonal-bipyramidal and distorted octahedral geometries around Sn, respectively. The ligand and several of the new compounds are good antimicrobial agents.     

Synthesis and characterization of new platinum(II) phosphinate complexes

The syntheses of platinum(II) complexes of bis(dimethylphosphinylmethylene)amine and bis(aminomethyl)phosphinic acid were investigated. In the case of bis(dimethyl-phosphinylmethylene)amine the reaction with K₂[PtCl₄] yields the potassium amino-trichloroplatinate K[PtCl₃L] (L?=?bis(dimethylphosphinylmethylene)amine), which was characterized by multinuclear (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) NMR spectroscopy in solution. Bis(aminomethyl)phosphinic acid reacts with K₂[PtCl₄] under strictly controlled pH conditions to give colorless crystals of the cisplatin analog K[PtCl₂L′] (L′?=?bis(aminomethyl)phosphinate). This complex was characterized by multinuclear NMR spectroscopy in solution as well as by single-crystal X-ray diffraction in the solid state. The bis(aminomethyl)phosphinate coordinates to platinum via both amino functions, thus acting as a chelating ligand.     

硅表面复合自组装膜的制备及其摩擦性能

采用自组装技术在单晶硅表面制备了3-氨基丙基三乙氧基硅烷(APTES)-SiO2-APTES复合膜,并对其表面的组成、结构及摩擦性能进行了表征.结果表明:复合膜表面对水的接触角约为63°,且表面平整、致密,其平均粗糙度(Ra)约为0.963nm.通过原子力显微镜(AFM)和透射电子显微镜(TEM)观察到夹层中SiO2颗粒的粒径约为20-50nm,较均匀地分布在第一层APTES膜的表面.与APTES自组装单层膜(SAMs)相比,APTES-SiO2-APTES复合膜由于纳米SiO2颗粒的引入而表现出更低的摩擦系数和更长的耐磨寿命.