Complexation inner-sphere

For kaolinite the sample permeability was very low and the solution was poorly removed. The spectra (Figure 3C) are consequently complex, containing peaks for inner and outer sphere complexes, CsCl precipitate from resMual solution (near 200 ppm) and a complex spinning sideband pattern. Spectral resolution is poorer, but at 70% RH for instance, inner sphere complexes resonate near 16 ppm and outer sphere complexes near 31 ppm. Dynamical averaging of the inner and outer sphere complexes occurs at 70% RH, and at 100% RH even the CsCl precipitate is dissolved in the water film and averaged. 

For illite and kaolinite with decreasing solution concentration (Figure 5) there are two important changes. The relative intensity for inner sphere complexes increases, and the chemical shifts become substantially less positive or more negative due to the reduced Cs/water ratio, especially for the outer sphere complexes. Washing with DI water removes most of the Cs in outer sphere complexes and causes spectral changes parallel to those caused by decreasing solution concentration (data not shown). 

The surface behavior of Na is similar to that of Cs, except that inner sphere complexes are not observed. Although Na has the same charge as Cs, it has a smaller ionic radius and thus a larger hydration energy. Conseguently, Na retains its shell of hydration waters. For illite (Figure 6), outer sphere complexes resonate between -7.7 and -1.1 ppm and NaCl... 

Differentiation between inner- and outer-sphere complexes may be possible on the basis of determination of activation volumes of dediazoniations catalyzed by various metal complexes, similar to the differentiation between heterolytic and homolytic dediazoniations in DMSO made by Kuokkanen, 1989 (see Sec. 8.7). If outer-sphere complexes are involved in a dediazoniation, larger (positive) volumes of activation are expected than those for the comparable reactions with inner-sphere complexes. Such investigations have not been made, however, so far as we are aware. 

The species (MS03)" represents an inner-sphere complex between sulphite and the oxidant formed by ligand-displacement. (MS03)" is formed by abstracting an electron from... 

Fig. 5. A model for S042- substitution on [Be(H20)4]2+ proceeding from the outer-sphere complex on the left through the transition state at center to the inner-sphere complex at the right of the figure (16, 66).

Copper also binds very strongly as an inner-sphere complex with organic matter while other divalent transition metals such as Ni2+ and Co2+... 

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Chloroform solutions of calixarenes (33 38)293,354 show high affinity for Au111 and good selectivity over Fe111 in some cases.293 Spectroscopic data indicate that complex formation with thioethoxy calix[4]arenes involves formation of inner-sphere complexes with Au—S bonds.354... 

Inner sphere complexes are formal with Pd11,... 

An inner-sphere complex (42) is formed when toluene solutions of 3,3-diethylthietane are contacted with solutions of Prv in hydrochloric acid, but extraction is slow 322... 

It is important to distinguish between outer-sphere and inner-sphere complexes. In inner-sphere complexes the surface hydroxyl groups act as o-donor ligands which increase the electron density of the coordinated metal ion. Cu(II) bound inner-... 

Surface complex formation of an ion (e.g., cation) on the hydrous oxide surface. The ion may form an inner-sphere complex ("chemical bond"), an outer-sphere complex (ion pair) or be in the diffuse swarm of the electric double layer. (From Sposito, 1989)... 

Fig. b shows a schematic portrayal of the hydrous oxide surface, showing planes associated with surface hydroxyl groups ("s"), inner-sphere complexes ("a"), outer-sphere complexes ("P") and the diffuse ion swarm ("d"). (Modified from Sposito, 1984)... 

Direct evidence for inner-sphere complexes comes from spectroscopic methods unfortunately, spectroscopic methods alone are seldom sufficiently sensitive to reveal the specific structure of surface complexes. Motschi (1987) used electron... 

As we shall see (Chapter 4), the kinetics of surface complex formation is often related to the rate of H20 loss from the aquo cation. This is another (indirect) evidence for inner-sphere complex formation. 

We can simplify by considering that k.- k.w, and by setting k k-i = Kos. Kos is the equilibrium constant of the outer sphere complex. For the rate of the formation of MeLJ2 n)+ inner-sphere complex (now written without water), we have... 

The mechanism given is in support of the existence of inner-sphere surface complexes it illustrates that one of the water molecules coordinated to the metal ion has to dissociate in order to form an inner-sphere complex if this H20-loss is slow, then the adsorption, i.e., the binding of the metal ion to the surface ligands, is slow. 

Standard cations used for measuring cation exchange capacity are Na+, NHJ, and Ba2+. NH is often used but it may form inner-sphere complexes with 2 1 layer clays and may substitute for cations in easily weathered primary soil minerals. In other words, one has to adhere to detailed operational laboratory procedures these need to be known to interpret the data and it is difficult to come up with an operationally determined "ion exchange capacity" that can readily be conceptualized unequivocally. 

The reactivity of the surface (Fig. 5.3), i.e., its tendency to dissolve, depends on the type of surface species present e.g., an inner-sphere complex with a ligand such as that shown for oxalate... 

V Specifically adsorbed species are those that are bound by interactions other than electrostatic ones. To what extent SO and Ca2+ can form inner-sphere complexes is not yet well established. SO2 is able to shift the point of zero proton condition of many oxides. 

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