Eigen-type mechanism

The rates of formation of Ni(II) complexes with selected monodentate ligands are given in Table 6. The following Eigen-type mechanism (also described as Sn 1 IP [78], or Ij [79])... 

Picolinic acid (pyridine 2-carboxylic acid) complexes of chromium(III) have been the subject of a number of studies. Complexation by picolinic acid in water/ethanol (30% v/v) follows an ion-pairing, Eigen-Wilkins type mechanism.Activation parameters suggest an associative character for the reaction of the aqua complex. Chelated complexes of chromiuni(ni) and picolinic acid are the products of the rapid, inner-sphere reduction of [Co (pico)(NH3)5p with chromium(II). The reaction of the related 4-carboxylic acid complex of cobalt(III) with chromium(II) is also rapid in contrast, pyridine-3-carboxylic acid (nicotinic acid) complexes undergo slower reactions. A -hydroxy-bridged dimeric complex [Cr2(pico)4(OH)2] has also been prepared. A study of magnetic properties in the temperature range 16-300 K leads to J - —6 cm and g = 2, typical for such complexes. 

In order to obtain some more support for this hypothesis we have conducted experiments in mixed solvents. This procedure was dictated by the following considerations. For a two step mechanism of the usual Eigen type... 

Fig. 6. Deprotonation of acetylacetone by bases [21]. The points fall below the line predicted by the classical Eigen mechanism [21] and are correlated by a Marcus type equation.

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