Second-Sphere Donor-Acceptor Interactions in Excited States of Coordination Compounds. Ruthenium(II) Bipyridine Cyano Complexes

Donor-acceptor interactions at the periphery of a coordination compound can have important consequences on its photochemical and photophysical behavior. Effects of this type have been explored using Ru(II) bipyridine complexes containing cyanide ligands. The cyanide ligands of these complexes behave as electron donors in interactions with acceptor solvents, protonation, methylation, and bridging to other metals with formation of polynuclear complexes. A variety of effects have been observed, ranging from (i) weak perturbations of the properties of the original complex, to (ii) major changes in the photophysical behavior of the complex via changes in redox potentials and excited state energy ordering, to (iii) induction of completely new properties characteristic of the complex-acceptor “supermolecule”. Examples of such effects are discussed in some detail. The use of second-sphere donor-acceptor interactions to tune excited-state properties is stressed. © 1988 IUPAC