REDOX AND pH-INDUCED SWITCHING OF THE COORDINATION SITES IN THE 3-HYDROXYPICOLINATE RUTHENIUM(III)-edta COMPLEX

摘要

Ruthenium(III)-edta reacts with the 3-hydroxypicolinate ligand (Hhpic~-) at pH 5, yielding the practically colorless (Ru~(III)(edta)(#kappa#N, #kappa#O-Hhpic))~(2-) complex (H_2hpic = 3-hydroxypicolinic acid; H_4edta = ethylenedinitrilotetraacetic add). Above pH 9, deprotonation of the phenolic group promotes an intramolecular linkage isomerization process, generating the faint red (Ru~(III)(edta)(#kappa#N, #kappa#O-hpic))~(3-) complex. Both isomers can be electrochemically reduced, converting into a single deep red (Ru~(III)(edta)(#kappa#N, #kappa#O -Hhpic))~(3-) complex strongly stabilized by ruthenium-to-pyridinecarboxylate d_(#pi#)-> P_(#pi#)~* charge-transfer interactions. The observed distinct binding properties as a function of the oxidation states and pH have been rationalized based on semiempirical theoretical calculations for the complexes.