Ammine electron transfer between

Figure 2. Deuterium isotope effect for electron transfer between ammine complexes as a function of the reduced electronic energy gap AE/EC where Er is the total reorganization energy E, = Eg + Ec. Key for parameters — —, hci)H/kBT — 2.0 and Es/Ec = 0 ------------------, Es/Ec = 1 and-------, Es/Ec = 2.

There are also charge-transfer characteristics within the electronic transitions between the spin-orbit states of the pentaammine complexes. This is evidenced by order of magnitude increases in the intensities of these transitions when an ammine or aqua ligand is replaced by a 77-base (e.g., Cl ) or a 7r-acid (e.g., N heterocycle) (67). 

Reactions of the type shown in Eq. (1.11), where L = isonicotinamide, 4-ethyl-pyridine, 3,5-lutidine, or pyridine, all exhibited volumes of activation for the forward reaction of between +3 and +7 cm mol compared to overall reaction volumes of between +19 and +26 cm mol . This indicates that electron transfer from Fe to Ru is characterized by an early transition state in terms of volume changes along the reaction coordinate (see Fig. 1.21). The overall volume changes could be accoimted for in terms of electrostriction effects centered around the ammine ligands on the ruthenium center. A number of possible explanations in terms of the effect of pressure on electronic and nuclear factors were offered to account for the asymmetrical nature of the volume profile 67]. 

Osmium(IV) ammines have unusually low pXa values (see Table 5) and so persist only in strongly acidic media the complexes are more acid by an order of five to six than their platinum(IV) counterparts but only slightly more acidic than the corresponding iridium(IV) complexes. This has been correlated with the decreasing t2g electron occupancy in the series PtIV-Irlv-OsIV and attributed to charge transfer from ligands to the empty n orbitals on osmium(IV). The cis isomers are more acidic than the trans, and this can be correlated with differences between the osmium(III) and osmium(IV) complexes for the isomers.55... 

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