摘要:

Calix[4]arenes with 2-methylthioethoxy, 2-thiophenecarboxyethoxy, 2-N,N-dimethyl-dithiocarbamoylethoxy and 2-mercaptoethoxy groups on the lower rim, and with methanethiomethyl andN,N-dimethyldithiocarbamoylmethyl groups on the upper rim, have been used for the transfer of Sn(II), Hg(II), Ag(I), Pd(II), Au(III), Ni(II), Pt(II), MeHg(II), Pb(II) and Cd(II) from aqueous solution into chloroform. These compounds generally extract Hg(II), Ag(I), Au(III) and Pd(II), but not Ni(II), Pt(II), Pb(II) and Cd(II). A series of calix[4]arenes with amide and amine functionalities bound to the lower rim have been used as extractants for the anions HP42-, SeO42-, VO3−, ReO4−, CrO42-and MoO42-. The extraction data into chloroform from solutions having a pH of 0.85 and 7.0 generally show that the amines are better extractants than the amides, and that the former are most effective from acidic solutions.

ISSN:0260-3594    

DOI:10.1080/02603599908021442

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The construction and investigation of photoresponsive and redox-active supramolecular systems with acetylenyl (polyyne) and cumulenic sp hybridized carbon chains (Cn) are reported here. Novel types of one-dimensional rigid molecular rods and macrocyclic molecular squares with controllable and yet fixed chain lengths or cavity sizes are explored. Such systems will have the desired features such as synthetic accessibility, coordination versatility, rigidity, directionality, photostability, electronic conductivity, controllable distances between donors and acceptors, and controllable cavity sizes in macrocyclic molecular squares. These features are extremely important to the future applications of these new rigid supramolecular systems in molecular photonic and electronic devices, light-energy conversion, molecular recognition, and host-guest chemistry.

ISSN:0260-3594    

DOI:10.1080/02603599908021443

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A so-called “catalytic membrane sensor” (CMS) is being developed to impart selectivity and reactivity to the surface of an existing sensor by modifying it with a series of thin films. The proposed “sandwich-type” modification involves deposition of a catalyst layer between two size selective sol-gel layers on a Pd/Ni resistive H2sensor. The role of the catalyst is to convert organic materials to H2and organic by-products by a dehydrogenation mechanism. The roles of the membranes are to impart chemical specificity by molecular sieving of the analyte and the converted product streams as well as to control access to the underlying Pd/Ni sensor. The “sandwich” modification will mediate the sensor response and avoid potential poisoning effects. Ultimately, an array of these CMS elements encompassing different catalysts and membranes will further enable improvements in selectivity and specificity via pattern recognition methodologies. This report details the synthesis of the various thin film solutions (i.e., catalyst precursors, sol-gel solution), the generation of the catalyst through ion-exchange, a comparison of the double alkoxide versus standard catalyst precursors, and the processing required to generate a CMS. This paper also details the novel and surprising experimental data concerning the increased selectivity and durability observed for the sol-gel modified H2gas sensing resistors. The utility of the CMS component as a multi-molecular detector will be reported later.

ISSN:0260-3594    

DOI:10.1080/02603599908021444

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The structural diversity displayed by polymetallic cages is discussed, concentrating on the chemistry of cobalt and nickel stabilised by carboxylate and pyridonate ligands. The structures can be broken down into “families of cages”, five of which are identified. Adamantine-cages have been made with hepta- and nona-nuclear cores. Tricapped trigonal prisms with deca-, undeca- and dodeca-nuclear metal arrays have been made for Co and Ni, and related cages for Cr and Fe have also been synthesised. Perhaps the most aesthetically pleasing family are the metal wheels, which vary in nuclearity from eight to eighteen, and which have been found for the metals from Ti to Ni - excluding Mn. Cages based on oligomers of cubanes form the fourth family, and the fifth group is related to simple mineral archetypes such as the rock-salt or cadmium iodide structure.

ISSN:0260-3594    

DOI:10.1080/02603599908021445

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The use of mixed-oxides containing CeO2as oxygen storage/release components is discussed with special focus on the applications of these materials in auto-exhaust catalytic converters. Ceria easily forms solid solutions with transition-metal/rare-earth oxides over a wide composition range. The incorporation of dopants like Zr4+, Pr3/4+, Tb3/4+into the cubic fluorite lattice of CeO2strongly affects the structural and energetic properties of the materials by lowering activation energy for oxygen migration and by increasing reducibility of the cerium cation. This augments both total and kinetic oxygen exchange between the solid and the gas phase under conditions typically encountered in real systems.

ISSN:0260-3594    

DOI:10.1080/02603599908021446

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Based on an example of the dissolution process of calcium apatites, a new chemical approach to elaboration of basic dissolution mechanisms of inorganic solids in liquids at the atomic (ionic) level has been proposed and discussed The approach is based on experimental results on the surface state analysis, passed through the logic of chemical equations, and describes the dissolution process as a sequence of the successive chemical reactions occurring on the solid — liquid interface. According to the approach elaborated, the chemical mechanism of apatite dissolution appears to be incongruent (non-stoichiometric) at the atomic (ionic) level.

ISSN:0260-3594    

DOI:10.1080/02603599908021447

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The perfect alternating CO/olefin copolymers constitute an important class of new materials. Their synthesis requires a catalyst; in general, the applied catalytic systems are formed by a palladium(II) salt, modified by diphosphine or dinitrogen chelating ligands, in the presence of a BrØnsted acid as cocatalyst and, frequently, an oxidant such as 1,4-benzoquinone. Alcoholic medium is generally preferred. This overview will report on the main catalytic systems based on bidentate nitrogen-donor chelating ligands; particular attention will be dedicated to the CO/styrene copolymerization. A detailed analysis of several parameters influencing the yield and the quality of CO/styrene polyketone will be presented, together with the discussion of the control of the stereochemistry of the insertion of styrene in the growing chain.

ISSN:0260-3594    

DOI:10.1080/02603599908021448

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Hybrid organic-inorganic materials, in which organic and inorganic components are combined over a length scale ranging from a few Angstroms to a few tens of nanometers, are nanocomposites which offer huge potentialities for high added value applications. Numerous hybrid organic-inorganic materials have been developed in the past few years, mainly by taking advantage of the mild chemical conditions of the sol-gel process. Yet, the sol-gel process generally yields amorphous materials which exhibit some polydispersity in the size and composition of the inorganic components of the hybrids. Moreover, controlling the interactions between the inorganic and organic components is not an easy task. One possible solution to overcome the polydispersity problem and achieve better control of the interactions is to use perfectly defined inorganic nanobuilding blocks such as metal oxo-clusters which exhibit sizes around 10 Å. When properly functionalized, they can be assembled, without being damaged, into various types of structures. Examples taken from polyhedral oligomeric silsesquioxanes, monoorganotin oxo-clusters, transition metal oxo-clusters and organically modified polyoxometalates will be presented and discussed relative to their synthesis, functionalization and assembling strategies.

ISSN:0260-3594    

DOI:10.1080/02603599908021449

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0260-3594    

DOI:10.1080/02603599908021441

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor