Solvent exchange kinetics

High pressure processors, 13 411 High pressure scanning electron microscopy (hpsem), 16 466 High pressure solvent exchange kinetics studies, 13 433-435... 

The most comprehensive information about ion-solvent complex formation follows from potentiometric titrations and some NMR measurements. This applies to NMR studies with solutions of ions like aluminum(III), gallium(III), beryllium(II) or magnesium(II) which interact so strongly with the molecules of several dipolar solvents that the lifetime of the molecules in the solvation shell is very long. Then the solvent exchange kinetics is slow enough to observe in the NMR spectrum of the solvent separate lines for coordinated solvent molecules and for free solvent. 

Frank and Wen [Fr 57] and later Caldin and Bennetto [Be 71, Ca 73] looked for a correlation between the solvent-exchange kinetic parameters for divalent metal ions and the structural properties of the solvent. Tanaka [Ta 76] demonstrated a... 

This methodology is especially useful for labile paramagnetic systems, and many of the solvent-exchange kinetic parameters given in Tables 3.13 and 3.18 have been determined by this method. A further application is discussed in Section 4.1.2 and described in Figure 4.2. 

Solvent Exchange.—Kinetic parameters for water exchange at some d and d complexes of formula [ML5(OH2)] + are given in Table 21. A comparison of... 

R. van Eldik, ed.. Inorganic High Pressure Chemistry, Elsevier, Amsterdam, The Netherlands, 1986. High pressure coordination kinetics including solvent exchange, octahedral and four-coordinate substitution, electron transfer, photochemical, and bioinorganics are discussed. 

As an extension of the intermolecular self-exchange described above, the solvent-induced intramolecular electron exchange kinetics in radical anions of 1,3-dinitrobenzene [47] and benzene 1,3-dicarbaldehyde [48] have been studied by several authors (Freed and Fraenkel, 1964 Grampp et al., 1989, 1990b Shohoji et al, 1987). The advantage of [47] and [48] is their structural simplicity and their high stability, which allows measurements even in protic... 

Where solvent exchange controls the formation kinetics, substitution of a ligand for a solvent molecule in a solvated metal ion has commonly been considered to reflect the two-step process illustrated by [7.1]. A mechanism of this type has been termed a dissociative interchange or 7d process. Initially, complexation involves rapid formation of an outer-sphere complex (of ion-ion or ion-dipole nature) which is characterized by the equilibrium constant Kos. In some cases, the value of Kos may be determined experimentally alternatively, it may be estimated from first principles (Margerum, Cayley, Weatherburn Pagenkopf, 1978). The second step is then the conversion of the outer-sphere complex to an inner-sphere one, the formation of which is controlled by the natural rate of solvent exchange on the metal. Solvent exchange may be defined in terms of its characteristic first-order rate constant, kex, whose value varies widely from one metal to the next. 

A variety of geometries have been established with Co(II). The interconversion of tetrahedral and octahedral species has been studied in nonaqueous solution (Sec. 7.2.4). The low spin, high spin equilibrium observed in a small number of cobalt(Il) complexes is rapidly attained (relaxation times < ns) (Sec. 7.3). The six-coordinated solvated cobalt(ll) species has been established in a number of solvents and kinetic parameters for solvent(S) exchange with Co(S)6 indicate an mechanism (Tables 4.1-4.4). The volumes of activation for Co " complexing with a variety of neutral ligands in aqueous solution are in the range h-4 to + 1 cm mol, reemphasizing an mechanism. 

In what is now a classical study in enzyme kinetics, W. J. Albery and J. R Knowles developed a strategy for establishing a reaction coordinate diagram (shown in Fig. 2) for triose-phosphate isomerase catalysis using solvent exchange and kinetic isotope effect data. 

The exact mechanisms of the complex formation and dissociation processes are not known. The overall process is represented by equation (X). Conformational changes may occur. Bimolecular processes might contribute, especially in solvents of low polarity (see, however, 143). A limited number of exchange rates have been reported, based mainly on NMR data (Table 13). Exchange kinetics are of prime importance in transport processes, where, however, more complex mechanisms may be operative than in the systems described here (see below andp. 145). 

DNA cleavage by, 43 158-159 reactions, copper proteins, 39 25 Oxo-trichloroselenates(IV), 35 270-271 Oxo-type molybdenum enzyme, see Molybdenum enzymes, pterin-containing Oxovandium (IV), solvent exchange and ligand substitution, 42 47-49 Oxyanions, Groups VIB and VIIB, redox reactions, kinetics and mechanism, 40 269-274... 

Table II Kinetic Data for Solvent Exchange and Formation of Complexes of Bivalent Transition Metal Ions In Methanol at 25°C ...

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