Theoretical Perspectives on Redox "Non-Innocent" Oxazolidine N-Oxide Iron Nitroxide Complexes

One-electron redox processes in ligands that exhibit non-innocent behaviour invariably leads to the generation of radical species, which, when coupled with redox-active metal centres, can lead to strong magnetic exchange, ambiguous electronic structures and even spin crossover (SCO). We have chosen two iron complexes [Fe-II(L-center dot)(2)](BF4)(2) (1) and [Fe-III(L-)(2)](BPh4) (2) [with L-center dot = 4-dimethyl-2,2-di(2-pyridyl)oxazolidine N-oxide] as the basis for an extensive theoretical study to determine the influence and interplay of the strong magnetic exchange, the redox non-innocent behaviour and any possible spin transitions. A series of calculations established the low-spin character of the Fe in both the complexes and gave us valuable insight into the electronic structure of 1 and 2 along with their one- and two-electron reduced species. An attempt has been made to relate the bonding features to the energy difference between different spin states and to the influence of the exchange coupling on any possible SCO properties.