Distinguishing between inner- and

Reductions of various Co(ni) complexes by Fe(II) have been studied under high pressures . The motivation for performing such experiments resides in the possibility that the volume of activation (AF ), like the entropy of activation, might be a criterion for distinguishing between inner- and outer-sphere reactions. For reactions of the type... 

In the first EPR studies of Ti02 colloids doped with V4+ ions [48, 146-149, 118], an important question about the correct attribution of the observed lines to certain coordination centers arose. First, it was necessary to distinguish between inner and surface centers, and then, to determine the local environ-ment around V4+ ions in each of these main groups. This attribution could be done by comparison of the experimental spectrum parameters with those known for monocrystalline samples of the same oxides. As an example, Fig. 8.10 presents a significant difference between two types of V4+ centers... 

Nd(III) hypersensitive transitions have been used to distinguish between inner and outer sphere complexes in solutions [203]. 

Strawn, D. G., and D. L. Sparks. 1999. The use of XAFS to distinguish between inner- and outer-sphere lead adsorption complexes on Montmorillonite. J. Coll. Interface Sci. 216 257-269. 

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY Nuclear magnetic resonance (NMR) spectroscopy can be applied to aqueous samples and can distinguish between inner- and outer-sphere ion surface complexes. The adsorption behavior of the cations Cs+ and Na" " was studied on the surfaces of silica, boehmite, kaolinite, and illite (Kim and Kirkpatrick, 1997). Cesium was adsorbed both as inner-and outer-sphere surface complexes and in the diffuse layer, while Na was adsorbed only as outer-sphere surface complexes and in the diffuse layer. The adsorbed Na ions were fully hydrated, while the Cs ions had direct contact with the surface oxygen atoms. 

For this purpose it is possible to extend to a multiple oxide the one-site model of Johnson (1984), which provides a thermodynamic description of the double layer surrounding simple hydrous oxides. Briefly, in this model the double layer charge is divided into the charge inside the slip plane, slip plane a[d]. While occupied sites, a[tl] is obtained from the Poisson-Boltzmann equation. Note that unlike the triple-layer model (Davis et al., 1978) which allows ions to form surface complexes at two different planes (0 or / ) instead of al the slip plane only, this model does not distinguish between inner- and outer-sphere complexes. Expression of the... 

For labile complexes, it is often quite difficult to distinguish between inner and outer sphere complexes. To add to this confusion is the fact that formation constants for such labile complexes when determined by optical spectrometry are often lower than those of the same system determined by other means such as potentiometry, solvent extraction, etc. This has led some authors to identify the former as "inner sphere" constants and the latter as "total" constants. However, others have shown that this cannot be correct even if the optical spectrum of the solvated cation and the outer sphere complex is the same (4, 7). Nevertheless, the characterization and knowledge of the formation constants of outer sphere complexes are important as such complexes play a significant role in the Eigen mechanism of the formation of labile complexes (8) This model describes the formation of complexes as following a sequence ... 

Stragier H, Cross JO, Rehr JJ, Sorensen LB, Bouldin CE, Woicik JC (1992) Diffraction anomalous fine structure A new X-ray structural technique. Phys Rev Lett 69 3064-3067 Strawn DG, Scheidegger AM, Sparks DL (1998) Kinetics and mechanisms of Pb(II) sorption and desorption at the aluminum oxide-water interface. Environ Sci Technol 32 2596-2601 Strawn DG, Sparks DL (1999) The use of XAFS to distinguish between inner- and outer-sphere lead adsorption complexes on montmorillonite. J Colloid Interface Sci 216 257-269 Strawn DG, Sparks DL (2000) Effects of soil organic matter on the kinetics and mechanisms of ( ) sorption and desorption in soil. Soil Sci Soc Am J 64 144-156 Stumm W (1992) Chemistry of the Sohd-Water Interface. John Wiley Sons, Inc, New York... 

How to distinguish between inner- and outer-sphere complexes in aqueous solution -thermodynamics and other criteria. (S. Ahrland) p. 21. 

Several criteria help to distinguish between inner- and outer-sphere complexes, although not always unambiguously. For instance, Choppin (1971) and Choppin and Bertha (1973) have used the thermodynamic A// and A5 parameters. They have assigned, in aqueous solutions, a predominantly outer-sphere character to CL, Br, L, ClOj, NOj, sulfonate and trichloroacetate complexes and an inner-sphere character to F, lOj, SO and acetate complexes. Moreover, these authors have related this ordering to the pKa values of the ligands. On the other hand, a group of Russian authors have postulated that iimer- and outer- sphere complexes may be studied separately by spectrophotometric methods, but this is subject to some doubt (vide infra). 

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