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Transition-metal ions aqueous solutions

Lower oxidation states are rather sparsely represented for Zr and Hf. Even for Ti they are readily oxidized to +4 but they are undoubtedly well defined and, whatever arguments may be advanced against applying the description to Sc, there is no doubt that Ti is a transition metal . In aqueous solution Ti can be prepared by reduction of Ti, either with Zn and dilute acid or electrolytically, and it exists in dilute acids as the violet, octahedral [Ti(H20)6] + ion (p. 970). Although this is subject to a certain amount of hydrolysis, normal salts such as halides and sulfates can be separated. Zr and are known mainly as the trihalides or their derivatives and have no aqueous chemistry since they reduce water. Table 21.2 (p. 960) gives the oxidation states and stereochemistries found in the complexes of Ti, Zr and Hf along with illustrative examples. (See also pp. 1281-2.)... [Pg.958]

The differential capacitance method cannot be used for reactive metals, such as transition metals in aqueous solutions, on which the formation of a surface oxide occurs over a wide potential re ion. An immersion method was thus developed by Jakuszewski et al. 3 With this technique the current transient during the first contact of a freshly prepared electrode surface with the electrolyte is measured for various immersion potentials. The electrode surface must be absolutely clean and discharged prior to immersion.182-18 A modification of this method has been described by Sokolowski et al. The values of obtained by this method have been found to be in reasonable agreement with those obtained by other methods, although for reactive metals this may not be a sufficient condition for reliability. [Pg.38]

A determination of dimethyl sulphoxide by Dizdar and Idjakovic" is based on the fact that it can cause changes in the visible absorption spectra of some metal compounds, especially transition metals, in aqueous solution. In these solutions water and sulphoxide evidently compete for places in the coordination sphere of the metal ions. The authors found the effect to be largest with ammonium ferric sulphate, (NH4)2S04 Fe2(S04)3T2H20, in dilute acid and related the observed increase in absorption at 410 nm with the concentration of dimethyl sulphoxide. Neither sulphide nor sulphone interfered. Toma and coworkers described a method, which may bear a relation to this group displacement in a sphere of coordination. They reacted sulphoxides (also cyanides and carbon monoxide) with excess sodium aquapentacyanoferrate" (the corresponding amminopentacyanoferrate complex was used) with which a 1 1 complex is formed. In the sulphoxide determination they then titrated spectrophotometrically with methylpyrazinium iodide, the cation of which reacts with the unused ferrate" complex to give a deep blue ion combination product (absorption maximum at 658 nm). [Pg.118]

In fact, the converse is observed. The main features of the spectra of transition metal ions in solution are very similar to those for crystal lattices where the same donor atom is present as an anion. Further, the spectra differ little between solids provided the nearest-neighbour atom is unchanged, even if it is part of a multi-atom species and even if the symmetry of the crystal structure is low. The spectra of the first transition series carbonates, for example, are not markedly different from those of their oxides, nor from those of the ions in aqueous solution. In each case the nearest-neighbour atom is oxygen and six of these surround the metal atom in approximately octahedral positions. [Pg.219]

Abstract - The structures of aqua and ammine complexes of transition metals in aqueous solutions were determined by the X-ray diffraction method at 25°C. The structures of some ethy-lenediamine complexes were also studied under the same experimental conditions. All of the aqua complexes studied, except the silver(I) complex, have six water molecules in their first hydration sphere. Silver(I) ion has only two water molecules in the linear form. In ammoniacal aqueous solutions, zinc(II) ion combines with at most four ammonia molecules to form the tetrahedral complex. The tetraamminecopper(II) complex has two more water molecules at the apices of a distorted octahedron. [Pg.67]

First, the use of water limits the choice of Lewis-acid catalysts. The most active Lewis acids such as BFj, TiQ4 and AlClj react violently with water and cannot be used However, bivalent transition metal ions and trivalent lanthanide ions have proven to be active catalysts in aqueous solution for other organic reactions and are anticipated to be good candidates for the catalysis of aqueous Diels-Alder reactions. [Pg.48]

The aromatic shifts that are induced by 5.1c, 5.If and S.lg on the H-NMR spectrum of SDS, CTAB and Zn(DS)2 have been determined. Zn(DS)2 is used as a model system for Cu(DS)2, which is paramagnetic. The cjkcs and counterion binding for Cu(DS)2 and Zn(DS)2 are similar and it has been demonstrated in Chapter 2 that Zn(II) ions are also capable of coordinating to 5.1, albeit somewhat less efficiently than copper ions. Figure 5.7 shows the results of the shift measurements. For comparison purposes also the data for chalcone (5.4) have been added. This compound has almost no tendency to coordinate to transition-metal ions in aqueous solutions. From Figure 5.7 a number of conclusions can be drawn. (1) The shifts induced by 5.1c on the NMR signals of SDS and CTAB... [Pg.145]

The latter reactions are catalyzed by a number of transition metal ions which can exist in several oxidation states in aqueous solution, e.g.,... [Pg.145]

Organic hydroperoxides have also been used for the oxidation of sulphoxides to sulphones. The reaction in neutral solution occurs at a reasonable rate in the presence of transition metal ion catalysts such as vanadium, molybdenum and titanium - , but does not occur in aqueous media . The usual reaction conditions involve dissolution of the sulphoxide in alcohols, ethers or benzene followed by dropwise addition of the hydroperoxide at temperatures of 50-80 °C. By this method dimethyl sulphoxide and methyl phenyl sulphoxide have been oxidized to the corresponding sulphone in greater than 90% yields . A similar method for the oxidation of sulphoxides has been patented . Unsaturated sulphoxides are oxidized to the sulphone without affecting the carbon-carbon double bonds. A further patent has also been obtained for the reaction of dimethyl sulphoxide with an organic hydroperoxide as shown in equation (19). [Pg.976]

Chemiluminescence from lucigenin is observed even without the catalytic transition metal ions but it is more intense when these ions are used. In aqueous or predominately aqueous solutions the CL yield is 0.01-0.02, which makes it a slightly better emitter than luminol [35], The emission of lucigenin is also catalyzed by Pb(II), Bi(III), Tl(III), and Hg(I) ions, which do not catalyze the CL of luminol [36],... [Pg.112]

The thermodynamic functions (AH, AS, AG(298 K)) of hydrogen peroxide reactions with transition metal ions in aqueous solutions are presented in Table 10.1. We see that AG(298K) has negative values for reactions of hydroxyl radical generation with Cu1+, Cr2+, and Fe2+ ions and for reactions of hydroperoxyl radical generation with Ce4+, Co3+, and Mn3+. [Pg.385]

Enthalpies, Entropies, and Gibb s Energies of Transition Metal Ion Oxidation-Reduction Reactions with Hydrogen Peroxide in Aqueous Solution (T = 298 K) [23]... [Pg.385]

The values of the rate constants for the reactions of transition metal ions with hydrogen peroxide in an aqueous solution are presented in Table 10.2. [Pg.387]

Rate Constants of Transition Metal Ion Reactions with Hydrogen Peroxide in Aqueous Solutions... [Pg.387]

Peroxyl radicals with a strong oxidative effect along with ROOH are continuously generated in oxidized organic compounds. They rapidly react with ion-reducing agents such as transition metal cations. Hydroxyl radicals react with transition metal ions in an aqueous solution extremely rapidly. Alkyl radicals are oxidized by transition metal ions in the higher valence state. The rate constants of these reactions are collected in Table 10.5. [Pg.395]

Ketones are resistant to oxidation by dioxygen in aqueous solutions at T= 300-350 K. Transition metal ions and complexes catalyze their oxidation under mild conditions. The detailed kinetic study of butanone-2 oxidation catalyzed by ferric, cupric, and manganese complexes proved the important role of ketone enolization and one-electron transfer reactions with metal ions in the catalytic oxidation of ketones [190-194],... [Pg.407]

LOMI [Low oxidation metal ions] A process for decontaminating parts of nuclear reactors by washing with aqueous solutions of low-valency transition metal ions. Developed at the Berkley laboratories of the UK Atomic Energy Authority in the early 1980s. [Pg.166]

Redox potentials of transition metal ions in aqueous solutions... [Pg.81]

The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free metal ions extracted by a perspiration solution [53]. Histidine (5.67) is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such chromogens by the combined effects of perspiration and sunlight. The absorption of histidine by cellophane film from aqueous solution was measured as a function of time of immersion at various pH values. On addition of histidine to an aqueous solution of a copper-complex azo reactive dye, copper-histidine coordination bonds were formed and the stability constants of the species present were determined [54]. Variations of absorption spectra with pH that accompanied coordination of histidine with copper-complex azo dyes in solution were attributable to replacement of the dihydroxyazo dye molecule by the histidine ligand [55]. [Pg.265]

Coordinative Environment. The coordinative environment of transition metal ions affects the thermodynamic driving force and reaction rate of ligand substitution and electron transfer reactions. FeIIIoH2+(aq) and hematite (a-Fe203) surface structures are shown in Figure 3 for the sake of comparison. Within the lattice of oxide/hydroxide minerals, the inner coordination spheres of metal centers are fully occupied by a regular array of O3- and/or 0H donor groups. At the mineral surface, however, one or more coordinative positions of each metal center are vacant (15). When oxide surfaces are introduced into aqueous solution, H2O and 0H molecules... [Pg.451]

Even in an excess of ligands capable of stabilizing low oxidation state transition metal ions in aqueous systems, one may often observe the reduction of the central ion of a catalyst complex to the metallic state. In many cases this leads to a loss of catalytic activity, however, in certain systems an active and selective catalyst mixture is formed. Such is the case when a solution of RhCU in water methanol = 1 1 is refluxed in the presence of three equivalents of TPPTS. Evaporation to dryness gives a brown solid which is an active catalyst for the hydrogenation of a wide range of olefins in aqueous solution or in two-phase reaction systems. This solid contains a mixture of Rh(I)-phosphine complexes, TPPTS oxide and colloidal rhodium. Patin and co-workers developed a preparative scale method for biphasic hydrogenation of olefins [61], some of the substrates and products are shown on Scheme 3.3. The reaction is strongly influenced by steric effects. [Pg.63]


See other pages where Transition-metal ions aqueous solutions is mentioned: [Pg.170]    [Pg.118]    [Pg.1340]    [Pg.342]    [Pg.1049]    [Pg.976]    [Pg.578]    [Pg.71]    [Pg.21]    [Pg.95]    [Pg.198]    [Pg.370]    [Pg.24]    [Pg.159]    [Pg.311]    [Pg.349]    [Pg.354]    [Pg.376]    [Pg.60]    [Pg.24]    [Pg.56]    [Pg.78]    [Pg.430]    [Pg.158]    [Pg.197]    [Pg.287]   
See also in sourсe #XX -- [ Pg.966 ]

See also in sourсe #XX -- [ Pg.1000 ]




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Aqueous ions

Aqueous solution, ion

Metal ion solution

Metal ions aqueous solution

Metal solutions

Solute ions

Solution transition metal ions

Solutions metallic

Transition ions

Transition metal ions

Transition metals, aqueous

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