Search results for "exchange"
showing 10 items of 2035 documents
Superexchange pathways in oxovanadium(IV) phosphates
1992
Abstract Oxovanadium(IV) phosphates show a diversity of magnetic behaviours that cannot be deduced from their respective structural features only. In part, this is due to the involvement of phosphate bridges in the spin transfer between V(IV) centres, and 31P solid state nuclear magnetic resonance becomes a key tool in determining the exchange mechanisms. The magnetic properties of a wide set of vanadium(IV) containing derivatives can be explained by realizing that a good overlap of the magnetic orbits may be achieved through paths involving phosphorus d orbitals.
PBI-based composite membranes for polymer fuel cells
2010
Abstract In the present study poly(2,2-(2,6-pyridin)-5,5-bibenzimidazole) was used for the preparation of novel MEAs for high-temperature polymer fuel cells (HT-PEMFCs). We prepared hybrid materials with two types of silica fillers in order to increase the MEA performances using this polymer. The membranes were characterized in terms of their microstructure and thermal stability. Cell operation tests and Electrochemical Impedance Spectroscopy were used for the characterization of the MEAs. A maximum power density of about 80 mW cm−2 was obtained at 300 mA cm−2 by using an imidazole-modified silica filler. The EIS technique showed that the fillers chiefly help to reduce the charge transfer r…
Electronic Perspective on the Electrochemistry of Prussian Blue Films
2009
The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue (PB) voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic or…
Multivalent ion-exchange model of biopolymer chromatography for mass overload conditions
1991
Abstract The simple model of multivalent ion-exchange biopolymer chromatography is analyzed on the basis of classical quasi-chemical temperature. The rigorous isotherm equation deduced from the stoichiometric displacement model (SDM) was used to stimulate the migration of a solute through the chromatographic column in the isocratic and gradient elution modes. The peak profiles generated for various sample sizes were compared with those obtained on the basis of a Langmuir isotherm. Peak tailing increases with the value of the exponent Z, defined as the ratio of the protein valency to the displacing counter-ion valency. For large Z the asymmetries due to the non-linearity of the isotherm are …
Dinuclear copper(II) complexes as testing ground for molecular magnetism theory
2019
Abstract A leitmotiv in the field of molecular magnetism is the study of the electron exchange (EE) magnetic interactions among distant metal centers through the corresponding bridging ligands in polynuclear coordination compounds. The present review provides a historical perspective on the use of dinuclear copper(II) complexes with either simple inorganic or extended organic bridging ligands as experimental and theoretical models for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the EE interaction across σ- and π-type orbital pathways. Particular focus is placed on the work by Professor Miguel Julve, outstanding researche…
Molecular squares of Ni(II) and Cu(II): ferromagnetic exchange interaction mediated by syn-anti carboxylate-bridging.
2009
The synthesis of four discrete tetranuclear complexes {[Ni(II)(L(2))][ClO(4)]}(4).MeCN (1), {[Cu(II)(L(1))(O(3)SCF(3))]}(4).H(2)O (), {[Cu(II)(L(3))(OClO(3))]}(4).MeCN () and {[Cu(II)(L(4))][ClO(4)]}(4).3MeCN.4H(2)O (4), supported by a closely similar group of carboxylate-appended (2-pyridyl)alkylamine ligands [L(1)(-): 3-[N-methyl-{2-(pyridin-2-yl)ethyl}amino]propionate; L(2)(-): 3-[(2-(pyridin-2-yl)ethyl){2-(pyridin-2-yl)methyl}amino]propionate; L(3)(-): 3-[N-isopropyl-{2-(pyridin-2-yl)methyl}amino]propionate and L(4)(2-): 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)] is described. Structural characterization reveals that each Ni(II) centre in 1 has square-pyramidal Ni(II)N(3)O(2) …
Synthesis and characterization of bisulfonated poly(vinyl alcohol)/graphene oxide composite membranes with improved proton exchange capabilities
2020
Abstract Composite membranes based on poly(vinyl alcohol) (PVA) and graphene oxide (GO) were prepared by solution-casting method to be used as proton exchange membranes (PEMs) in fuel cell (FC) applications. Bisulfonation was employed as a strategy to enhance the proton conductivity of these membranes. First, a direct sulfonation of the polymer matrix was accomplished by intra-sulfonation of the polymer matrix with propane sultone, followed by the inter-sulfonation of the polymer chains using sulfosuccinic acid (SSA) as a crosslinking agent. Furthermore, the addition of graphene oxide (GO) as inorganic filler was also evaluated to enhance the proton-conducting of the composite membranes. Th…
Influence of inheritance and pedogenesis on heavy metal distribution in soils of Sicily, Italy
2000
Abstract The recognition of the potential health hazards associated with heavy metals has focused attention on the levels and behaviours of these elements both in natural and contaminated environments. Various soil types developed from different parent materials in Sicily, Italy, have been analysed in order to compare heavy metal distribution under different geopedological conditions. Total metal concentrations, metal partitioning and distribution profiles are discussed in relation to the inheritance factor and pedogenic processes. Parent material composition largely influences the contents of heavy metals in most of the analysed soils, mainly differentiating pedons for their metal concentr…
Exploring the exchange interaction in a mixed valence {CoII4CoIII2} hexanuclear cluster with novel topology
2012
Abstract Reaction between [Co2(μ-OH2)(μ-Piv)2(Piv)2(HPiv)4] and a (salicylidene)ethanolamine ligand under ambient reaction conditions, affords hexanuclear complexes [CoIII2CoII4(Piv)8(HPiv)2(L)2(OH)2] (1–2). Both products have been characterized crystallographically and found to be mixed-valent, containing divalent and trivalent Co centers. Down to 30 K, the variable-temperature magnetic susceptibility data are dominated by the single-ion properties of high spin Co(II) centers with distorted-octahedral coordination geometries. Below this temperature, the effect of intramolecular ferromagnetic exchange interactions becomes apparent. Magnetic data has been analyzed in terms of ground isolated…
Post-Processing via Cation Exchange Cartridges: Versatile Options
2012
New 68Ge/68Ga radionuclide generators provide the positron emitter 68Ga (T½ = 67.7 min) as an easily available and relatively inexpensive source of a PET nuclide for labeling of interesting targeting vectors. However, currently available “ionic” 68Ge/68Ga radionuclide generators are not necessarily optimized for the routine synthesis of 68Ga-labeled radiopharmaceuticals in a clinical environment. Post-processing of 68Ge/68Ga generators using cation exchange resins provides chemically and radiochemically pure 68Ga with 97±2% within less than 4 min, with 68Ge almost completely removed, and ready for online labeling. This simple, fast, and efficient technology can be extended for new applicati…