Inner sphere, entropy reactions

In contrast to the situation observed in the trivalent lanthanide and actinide sulfates, the enthalpies and entropies of complexation for the 1 1 complexes are not constant across this series of tetravalent actinide sulfates. In order to compare these results, the thermodynamic parameters for the reaction between the tetravalent actinide ions and HSOIJ were corrected for the ionization of HSOi as was done above in the discussion of the trivalent complexes. The corrected results are tabulated in Table V. The enthalpies are found to vary from +9.8 to+41.7 kj/m and the entropies from +101 to +213 J/m°K. Both the enthalpy and entropy increase from ll1 "1" to Pu1 with the ThSOfj parameters being similar to those of NpS0 +. Complex stability is derived from a very favorable entropy contribution implying (not surprisingly) that these complexes are inner sphere in nature. 

J/m/K. The agreement between the nmr estimates and those from equation (1) add weight to the estimates in Table III. In Figure 2 the variation of log i and log 0 as functions of pKa reflect the vital role of ligand basicity in the inner-outer sphere competition. These curves indicate that the cross-over from predominantly outer sphere to predominantly inner sphere occurs near pKa values of 2. However, since the enthalpy and entropy changes for inner sphere complexation are larger than for outer sphere formation, both AH and AS would still be endothermic (characteristic of inner sphere reaction). 

The interpretation was that the entropy term was primarily responsible for the slow reaction in this case, and very approximately, a TAS value at 298.13 K of 20kJ mol compared to the experimental value of 27 kJ moP was obtained. However, it was pointed out that the quantitative interpretation needs to be considered with care, as ASjf is the total transition-state activation entropy and not only the inner-sphere reorganization part [452]. In addition, DFT-based studies have shown the importance of the influence of the second coordination sphere [453]. 

The TLM model has been applied not only to inorganic anions but also to organic species. In a study of 2,4-dichlorophenol, 2,4,6-trichlorophenol, andpentachlorophe-nol sorption in an allophanic soil (Cea et al. 2010), the isotherm experiments were well described (as shown in Figure 12.4) by the TLM in which monodentate outer and inner sphere complexes were considered to form between deprotonated organic molecules and active sites on the variable-charge soil. The calculated thermodynamic parameters suggest that chlorophenol sorption is a spontaneous (AG < 0), endothermic (AH > 0), and entropy-driven reaction (AS > 0). 

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... 

Relaxation of complicated ligands may occur as a step in both pathways. Diebler and Eigen 461 indicated the ways in which such mechanisms could be analysed using fast reaction methods. Several studies of Ln(III) complex formation and of the formation of Ln(III) mixed complexes have been analysed. Generally the dissociative mechanism is considered to dominate and we are then concerned with the water exchange rate. Several studies have shown that the rate decreases from La(III) to Lu(III) but there seems to be a minimum rate around Tm(III). This is also seen in the rate of rotation of ligands on the surface of the ions, Fig. 7. There may be a small crystal field term, or another contribution to a tetrad -like effect from the 4f electron core. However in the hydrate the precise relationship between the inner and outer sphere water may also be important as we saw when we discussed the heat and entropy of complex ion formation. 

The activation free energy for an outer-sphere electron transfer process, AG, consists of an internal contribution, AGin, associated with rearrangement of the inner-coordination spheres and an external contribution, AGSut, due to solvent rearrangement [equation (2)]. Reaction entropies, A5rc, for... 

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