Precursor Complexes of Known Structure

Precursor Complexes of Known Structure.—Work on a series of Co -Ru complexes has been described above (p. 8), and studies of mixed-valence systems, equivalent to symmetrical precursor complexes, are dealt with in a later section (P. 20). 

An attempt to generate an inert precursor complex with two cobalt centres has been alas unsuccessful. The isomeric dinuclear complexes shown at the left of equations (21) and (22) were used as starting materials. The Co (CN)6 group is 

Reaction (23) was also undertaken with the aim of generating a dinuclear complex, using the known affinity of the Fe(CN)6 group for the sulphur atom of DMSO. The 

Labile Dinuclear Lito-mediates—Direct Obs vation (Table 4).—Systems with labile dinuclear intermediates (precursor or successor complexes) continue to attract attention. When the reactants A+ and B form a sufficiently strong association complex, and the electron transfer is sufficiently slow, the equilibrium may reach saturation within the accessible range of concentration of one of the reactants. With one reagent (say A+) in excess, this leads to the Micbaelis-Menten rate law R=k[(AB) i = A i5r[A+][B]T/(l + A [A+]). In general, however, this still leaves open a mechanistic ambiguity the electron-transfer step may be the intramolecular reaction or it may be an independent bimolecular process A+ + B- A + B+. In effect, the form of the rate law provides an analytical method for determining the concentration of the dinuclear complex, but does not specify its role in the overall reaction. 

The reaction system (24) obeys the rate law (26),f consistent with the mechanism (25), with K = K, k =ki+kblKi, but in this case comparison with analogous systems 

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