From Nanoparticles to Non-Covalent Interactions: Electron Transfer in Inorganic Supramolecular Mixed Valence Systems

Understanding the intricacies of inner sphere electron transfer has been a challenge for nearly 50 years. Since the preparation of the Creutz-Taube ion extensive research in inorganic mixed valence systems has been performed. We employ coalescence of nu(CO) bandshapes observed in the 1-D infrared (IR) spectra of mixed valence complexes to determine rate constants of electron transfer (ET). Herein we report synthesis, characterization, and spectroscopy of Ru3O clusters bound to metallic nanoparticles, and report ET rates in the "ultrafast" regime. We observe that ET rates are faster when there is favorable electronic alignment between the Ru clusters and the Au nanoparticle. In addition, results show that ground state ET rate constants that are in the "ultrafast" regime depend on the pre-exponential term within the frequency factor, nuN, not the activation energy as expected in a system undergoing ergodic electron transfer.;We extended our knowledge of these complexes by studying ET at a semiconducting nanoparticle interface. Working in collaboration with Prof. Emily Weiss at Northwestern University, a complementary view of the parameters that govern ET in such systems has been developed by investigating ET rates between the triruthenium clusters and QDs. The photoinduced electron transfer rate from photoexcited CdSe QDs to triruthenium clusters having either a pyridine-4-carboxylic acid or a 4-mercaptopyridine linkage are reported. Results show that the intrinsic charge separation rate constant (kCS,int), is approximately seven times faster for a thiol linked cluster compared to a nicotinic acid bound cluster. Thus the charge transfer rates between colloidal quantum dots and redox-active ligands adsorbed to their surfaces can be tuned through the choice of the coordinating headgroup of the ligand.;We report that exchange of electrons across hydrogen bonds can increase the strength of typically weak interactions. A thermodynamically stable mixed valence dimer is obtained upon the one electron reduction of a Ru3O cluster with a isonicotinic acid ancillary ligand. Observed intervalence charge transfer bands (IVCT) indicate significant coupling between the two Ru centers through linked by a hydrogen bonding interaction. The IVCT bands are found to be best explained by a semi-classical 3-state model, further highlighting the importance of the bridging interaction in these systems. Additionally, we report that the electronic coupling between two metal centers can be modulated by simple ancillary ligand substitution. The wavefunction overlap of two metal centers bridged by a hydrogen bond is found to be non-zero.;We report a series of new Ru3O clusters with ancillary ligands capable of pi-stacking in solution upon a single electron reduction. Large splittings are observed berween the reductions in the electrochemical responses of these newly synthesized systems. The effects on the electrochemical splitting of the reduction waves by donating and withdrawing ligands on the "bridge" are compared. A crystal structure of the ground state shows no significant evidence of pi-pi interaction between clusters in solution.;The major themes of this thesis are the role of electronic coupling, Hab, on long range ET in supramolecular mixed valence systems, and the importance of the bridging interaction in modulating Hab in these systems.