The progress of ligand exchange reactions between the ligands of Au-25(SR)(18)(-) nanoparticles (SR = S(CH2)(2)Ph) and thiols with electron-withdrawing substituents (HSPh-p-X; X = Br, NO2) was monitored using nuclear magnetic resonance. As the reactions proceed, the introduction of the electron withdrawing SPhX ligands into the nanoparticle ligand shell causes a shift of the nanoparticle redox waves (Au25(1+/0)) and Au-25(0/1-)) to more positive potentials. Combining the NMR and electrochemical results reveals a nearly linear shift of the redox formal potentials as a function of the average number of exchanged ligands: similar to 42 and 25 mV/ligand for X = NO2 and Br, respectively. Using a simple model electron-withdrawing ligand (-SCH2Cl), density functional theory (DFT) was used to study in detail the effects on the nanoparticle electronic structure caused by exchange of this ligand for -SCH3. The calculations show how the electronegative X group changes the polarization of the nanoparticle and the chargedistribution among the ligands, the protecting (-SR-Au-SR-Au-SR) semirings, and the Au-13 core. The HOMO-LUMO gap is unchanged by the ligand exchanges; both states are equally stabilized by the presence of each incoming ligand, by 60 mV/ligand. Charge analysis suggests no significant changes in the Au-13 core, even after complete exchange. Rather, the charge is transferred inside the ligands, mostly from nearest-neighbor atoms of the semirings.
- REDOX POTENTIALS