Excited State Turn-On of Aurophilicity: A Computational Investigation of the Tunability of Relativistic Effects
CHARLES J ZEMAN IV, †,‡ ADAM S VEIGE, † AND KIRK S SCHANZE‡
†Department of Chemistry, Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, United States
‡Department of Chemistry, University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
A historically counterintuitive property, aurophilicity is described as a peculiarly strong bonding interaction between the metal centers of Au(I) complexes, despite being closed-shell atoms with unfavorable electrostatics. The explanation for this property lies in Van der Waals forces that have been augmented by the relativistic effects of core electrons, long known to be at a local maximum for Au atoms.1 Although aurophilicity has been the subject of extensive research, little has been done to investigate the transient existence of aurophilic interactions in excited states. This work examines a reported synthetic product2 that templates two Au(I) metal centers just outside of the sum of the Van der Waals radii of the two atoms (3.8 Å). By optimizing geometries in specified excited states that exhibit charge transfer character to the metal centers, contractions in the Au(I)-Au(I) distance were observed. A series of different aryl substituents were studied of different ionization potentials. It was found that the extent to which the Au(I)- Au(I) bond contracted in the excited state depended on the electron donating character of the substituent. By conducting this study with Hartree-Fock, post Hartree-Fock, and various Density Functional methods in conjunction with a series of basis sets that vary the degree to which electrons are treated relativistically, a definitive statement can be made about the efficacy and tunability of relativistic effects that only present themselves in the excited state while also showcasing the merits and plights of different levels of theory.
References
(1) Schmidbaur, H.; Schier, A. A Briefing on Aurophilicity. Chem. Soc. Rev. 2008, 37, 1931– 1951.
(2) Yang, X.; Wang, S.; Ghiviriga, I.; Abboud, K. A.; Veige, A. S. Organogold Oligomers: Exploiting IClick and Aurophilic Cluster Formation to Prepare Solution Stable Au4 Repeating Units. Dalt. Trans. 2015, 44, 11437–11443.