And water exchange reactions

Kinetic Parameters for Bridge-Formation and Water-Exchange Reactions of Ammine Complexes at 25°C in 1.0 A/(Na,H)CI04 ... 

Another factor that must be considered to rationalize the product stereochemistry is the isomerization rates of the starting complexes (as well as those of the products). Table 12.11 lists data for [Co(en)2(H20)X]" isomerization and water exchange reactions. 

Inada Y, Mohammed AM, Loefiler HH, Rode BM (2002) Hydration structure and water exchange reaction of Nickel(II) Ion classical and QM/MM simulations. J Phys Chem A 106 6783-6791 Jenkins HBD, Marcus Y (1995) Viscosity B-coefficients of ions in solution. Chem Rev 95 2695-2724... 

X. Jin, Y. Yan, W. Shi, S. Bi, Environ. Sci. Technol. 2011, 45, 10082-10090. Density functional theory studies on the structures and water-exchange reactions of aqueous Al(III)oxa-late complexes. 

Heavy water [11105-15-0] 1 2 produced by a combination of electrolysis and catalytic exchange reactions. Some nuclear reactors (qv) require heavy water as a moderator of neutrons. Plants for the production of heavy water were built by the U.S. government during World War II. These plants, located at Trad, British Columbia, Morgantown, West Virginia, and Savaimah River, South Carolina, have been shut down except for a portion of the Savaimah River plant, which produces heavy water by a three-stage process (see Deuterium and tritium) an H2S/H2O exchange process produces 15% D2O a vacuum distillation increases the concentration to 90% D2O an electrolysis system produces 99.75% D2O (58). 

Other transformations supplied by these enzymes are para-ortho-hydrogen conversion, and the exchange reaction between H2 and protons of water.409-412 The hydrogenase enzymes found in various microorganisms are very different in their protein structure and in the types of electron carrier they use. 

In the IPCM calculations, the molecule is contained inside a cavity within the polarizable continuum, the size of which is determined by a suitable computed isodensity surface. The size of this cavity corresponds to the molecular volume allowing a simple, yet effective evaluation of the molecular activation volume, which is not based on semi-empirical models, but also does not allow a direct comparison with experimental data as the second solvation sphere is almost completely absent. The volume difference between the precursor complex Be(H20)4(H20)]2+ and the transition structure [Be(H20)5]2+, viz., —4.5A3, represents the activation volume of the reaction. This value can be compared with the value of —6.1 A3 calculated for the corresponding water exchange reaction around Li+, for which we concluded the operation of a limiting associative mechanism. In the present case, both the nature of [Be(H20)5]2+ and the activation volume clearly indicate the operation of an associative interchange mechanism (156). 

Mechanistic details are very similar for DMSO and water exchange. The reaction proceeds through a distorted trigonal bipyramidal reactive intermediate [Li(DMSO)5]+ that is reached via a late transition state. The enthalpy profile (see Fig. 13) is in line with the experimentally observed very fast exchange process. The five-coordinate intermediate is computed to be 7.9kcalmol 1 less stable than [Li(DMS0)4]+ and free DMSO, while an overall activation barrier of only 8.4kcalmol 1 is computed. Obviously,... 

The simplest reactions to study, those of coordination complexes with solvent, are used to classify metal ions as labile or inert. Factors affecting metal ion lability include size, charge, electron configuration, and coordination number. Solvents can by classified as to their size, polarity, and the nature of the donor atom. Using the water exchange reaction for the aqua ion [M(H20) ]m+, metal ions are divided by Cotton, Wilkinson, and Gaus7 into four classes ... 

Judging from these findings, the mechanism of Lewis acid catalysis in water (for example, aldol reactions of aldehydes with silyl enol ethers) can be assumed to be as follows. When metal compounds are added to water, the metals dissodate and hydration occurs immediatdy. At this stage, the intramolecular and intermolecular exchange reactions of water molecules frequently occur. If an aldehyde exists in the system, there is a chance that it will coordinate to the metal cations instead of the water molecules and the aldehyde is then activated. A silyl enol ether attacks this adivated aldehyde to produce the aldol adduct. According to this mechanism, it is expected that many Lewis acid-catalyzed reactions should be successful in aqueous solutions. Although the precise activity as Lewis acids in aqueous media cannot be predicted quantitatively... 

In the simplest case, it can be assumed that the water exchange reaction with a complexing site of a heterogeneous ligand will be governed by the Eigen-Wilkens mechanism as for complexes with simple ligands. In this case, equations (26) and (29) can be combined to yield ... 

NiO O) (H). Recently Merbach and coworkers (12) have cited evidence for a gradual changeover of mechanism from 1 to 1 for the water exchange reactions of divalent metal ions in going... 

Pressure-decelerated water exchange reactions and evidence for dissociative interchange in corresponding net substitution reactions... 

In the literature there are only few studies on the water-exchange processes of the manganese(II) species in general (33,38- 1), and the only seven-coordinate Mn(II) complexes studied are [Mn(EDTA) (H20)] and its derivatives (38,39,42,43). Such studies are essential for understanding the mechanism of the manganese-containing SOD mimetics. The volume of activation for the water-exchange reaction... 

Activation Parameters and Rate Constants for The Water-Exchange Reaction... 

Activation volumes for water exchange on [M(0H)(H20)5] (Table V) are all more positive than those measured on the corresponding hexa-aqua ions indicating a more dissociative character for the water-exchange reaction. The decrease in the positive charge at the metal center loosens the metal-water bonds and facilitates rupture of the M-0 bond. 

Speciation is a dynamic process that depends not only on the ligand-metal concentration but on the properties of the aqueous solution in chemical equilibrium with the surrounding solid phase. As a consequence, the estimation of aqueous speciation of contaminant metals should take into account the ion association, pH, redox status, formation-dissolution of the solid phase, adsorption, and ion-exchange reactions. From the environmental point of view, a complexed metal in the subsurface behaves differently than the original compound, in terms of its solubility, retention, persistence, and transport. In general, a complexed metal is more soluble in a water solution, less retained on the solid phase, and more easily transported through the porous medium. 

The reactivity of aryltellurium trihalides decreases on going from the chlorides to the iodides, the same trend occurring for hydrolysis. Aryltellurium trichlorides are very sensitive to water and moisture and are easily hydrolysed, the tribromides being more stable, while the triiodides are unaffected by cold water and can be prepared even by aqueous procedures. Diaryltellurium dihalides are stable in water, and ionic exchange reactions allow the conversion of dichlorides into dibromides and diiodides. 

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