Spin-exchange processes in transition-metal complexes
Abstract
Rates of spin exchange (spin crossover) of some complexes of iron(II), iron(III) and cobalt(II) have been analysed by an intersecting-state model. Similarities in parameters with those observed in elementary gas-phase reactions suggests that the main energy barrier involves the internal reorganization of the coordination shell of the complex. Whilst the expected transition-state bond orders of one are observed with FeII and most CoII complexes, bond orders greater than one are observed in bis(terpyridyl)cobalt(II) and in FeIII complexes. This is explained in terms of involvement of non-bonding electrons in the transition state. In contrast to previous suggestions, nuclear tunnelling does not appear to be an important mechanism in spin exchange.