The Role of Bridging Groups

It is su sted that, in general, reactions of the first type will tend to involve net transfer of the bridging group, whereas the second type will not. In some cases, however, if not all, the argument is tantamount to rationalizing the relative inertness or lability of the metal centres before and after the reaction hence this theory overlaps with previous discussions to a considerable extent. 

Outer-sphere reactions are also considered. For the hypothetical reaction [Cr i Clsl +ECr Cls] , it is suggested that the inclusion of a Na+ ion in the transition state is sufficient to transform the reaction from non-adiabatic to adiabatic, and that the overall effects of counterions on such reactions are too great to be regarded as mere electrostatic stabilization of the encounter complex. Less credible is the conclusion that water molecules themselves can act as effective catalysts for outer-sphere electron transfer, a single water molecule between the reacting complexes leading to a resonance energy increase of 6 kcal mol . 

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The role of bridging groups in metal carbonyl cluster compounds is still not completely understood but has been discussed qualitatively by... 

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