Inner-sphere effect

A subsequent study by Shu and Rorabacher [122] has been directed at outer-sphere effects in methanol—water mixtures. To reduce inner-sphere effects to a minimum, a quinquedentate ligand (N-hydroxyethylethylene-diamine-N,N, N -triacetate, HEEDTA) was complexed to Ni(II) leaving a single coordination site available for ammonia—solvent exchange... 

The loss or gain of an electron by a molecule is typically accompanied by structural changes, which in turn also create a barrier to electron transfer. We are familiar with this effect in the gas phase when the transferred electron enters an antibonding orbital. Section 5.1.3.1. In solution, the barrier arising from intramolecular reorganization is known as an inner-sphere effect because it occurs within the solvation sphere. The barrier arising from solvent reorganization is then... 

Effect of Modulation of the Electron Density on the Inner-Sphere Activation... 

The effects of modulation of the electron density by the intramolecular vibrations on the process of inner-sphere activation... 

It is clear from the above equations that numerous parameters (proton exchange rate, kcx = l/rm rotational correlation time, tr electronic relaxation times, 1 /rlj2e Gd proton distance, rGdH hydration number, q) all influence the inner-sphere proton relaxivity. Simulated proton relaxivity curves, like that in Figure 3, are often used to visualize better the effect of the... 

Figure 3 Effect of the water exchange rate, kex, and the rotational correlation time, rR, on inner-sphere proton relaxivity. The plot was simulated for a particular value of the longitudinal electron spin relaxation rate, 1/Tie — 5.28xlOss 1. The marketed contrast agents all have relaxivities around 4—5mM 1s 1 in contrast to the theoretically attainable values over lOOrnM-1 s 1, and this is mainly due to their fast rotation...

The quantitative effects of steric encumbrance on the electron-transfer kinetics reinforce the notion that the inner-sphere character of the contact ion pair D+, A- is critical to the electron-transfer paradigm in Scheme 1. Charge-transfer bonding as established in the encounter complex (see above) is doubtless an important consideration in the quantitative treatment of the energetics. None the less, the successful application of the electron-transfer paradigm to the... 

The extent to which steric effects adversely affect the attainment of such intimate ion-pair structures would be reflected in an increase in the work term and concomitant diminution of the inner-sphere rate. This qualitative conclusion accords with the reactivity trend in Figure 16. However, Marcus theory does not provide a quantitative basis for evaluating the variation in the work term of such ion pairs. To obtain the latter we now turn to the Mulliken theory of charge transfer in which the energetics of ion-pair formation evolve directly, and provide quantitative informa-... 

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