Perturbation of the electronic structure of the Creutz-Taube ion via asymmetric encapsulation with macrocyclic ether species

Abstract

Ligand-bridged mixed-valence ions can exist in either valence-localized double-minimum ground potential energy surface or valence-delocalized (single-minimum ground PE surface) form. The determining factor is the balance between twice the initial-state/final-state electroniccoupling energy (H[sub if]) and the sum of the zeroth-order reorganization or trapping energy ([chi]) and any redox asymmetry [delta]E. For the Creutz-Taube ion (NH[sub 3])[sub 5[minus]] Ru[sup 11][sup 1/2](NH[sub 3])[sub 5][sup 5+], (1), redox asymmetry is absent, the valencies are completely delocalized, and 2H[sub if] evidently exceeds [epsilon]. We reasoned, however, that [open quotes]electronic isomerization[close quotes] to a valence-localized form might be possible if significant redox asymmetry could be introduced. We report here the introduction of the desired asymmetry in an unusual way: via binding of a macrocyclic ether to just one of the two available ruthenium ammine sites. We also report optical evidence for the onset of valence localization in both 1 and a trans pyridine (py) substituted analog (2), in the presence of either dibenzo-36-crown-12(DB-36-C-12) or dibenzo-30-crown-10 (DB-30-C-10) species. 17 refs., 3 figs.