Mixed complex term

A number of studies have been reported on complexes of bpy derivatives containing hydrocarbon chains, esters or amides in the 4,4 -positions (in some cases, only mixed complexes with bpy were studied). These somewhat hydrophobic compounds were generally examined in terms of energy transfer. While it is difficult to compare results... 

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. 

As indicated by the ellipses, Eq. (7) can be expanded to other exponential terms in [H+] as needed. If the metal and ligand tend to form mixed complexes of the type ML(OH), then the analogous expression can similarly be written as... 

In his first paper [240], Valiev considered the quadrupole relaxation of strongly solvated ions with the result that, for symmetrical solvation complexes, vibrations are chiefly causing relaxation, whereas for mixed complexes rotation of the whole solvate complex is dominating relaxation (cf. also Ref. [255]). As described above it appears from the recent paper by Hertz [239] that relaxation of symmetrically and strongly hydrated ions may be accounted for in terms of the motion of the water molecules in the second hydration sheath. 

The rate constants for the formation and dissociation of the mixed complex [Cu(bipy)(glycinate)]+ have been measured, and it was shown that, within experimental error, the rate-constant for attack by the glycine zwitterion is zero. For the reaction of Cu(bipy) + with the glycinate ion (gly), the forward rate constant is 1.6 x 10 lmol- s at 25 C. This compares with values of 4 x 10 lmol s for Cu + + gly and 4 X 10 lmol- s for Cu(gly)+ + gly and it is suggested that the differences can be accounted for in terms of statistical factors, char effects, and an enhancement term associated with the presence of bipy in the inner co-ordination sphere of the copper ion. A preliminary report shows that the rate of complex formation between the histaminium ion (6) and Cu"... 

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