Kinetically locked, trinuclear Ru-II metallo-macrocycles - synthesis, electrochemical, and optical properties

Using a [Ru-II([9] aneS(3))] templating moiety, kinetically-locked, metallomacrocycles incorporating adenine based ligands have been synthesised through self-assembly. The kinetically robust nature of these structures is confirmed by electrochemical studies: each can be reversibly oxidised in a four-member redox series, containing two formally mixed valence states. Unusually, the electrochemically derived comproportionation constants for these mixed valence states are very different, suggesting that intermetallic coupling differs between the two states. Spectroelectochemistry studies confirm that while the [Ru-II Ru-2(III)] state is valence localised, the [(RuRuIII)-Ru-II (2)] state is electronically delocalised. Mechanisms by which this switching effect could occur, which involve the unusual connectivities in these mixed valence species, are presented.