Symmetry breaking and effective motional averaging in double triangular clusters with exchange and electron transfer effects

The interplay of isotropic exchange, antisymmetric exchange, and electron delocalization has been theoretically investigated for a system comprising two triangles, one with three localized d¹ spins, which gives rise to spin frustration effects, and the other with one d¹ centre delocalized on the three sites. In the localized limit antisymmetric exchange is partially reduced by the low symmetry components of isotropic exchange (intertriangle interaction) and splits the spin triplets only in second order, contrary to what is found for a single triangular system where the splitting of the spin doublet levels occurs in first order. When the electron delocalization is introduced two different kinds of situations are found, depending on the symmetry of the electronic states. The orbital doublets of the delocalized system show full average of the exchange interactions, giving rise to effective enhancement of antisymmetric exchange. In the contrast the orbital singlets are unaffected by the transfer process, showing only second-order antisymmetric exchange. Coexistence of localized and delocalized states is expected to be an immanent feature of exchange systems with partial delocalization. The relevance of these effects on the magnetic properties of the clusters is briefly discussed.