Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2′:6′,2″-Terpyridine Ligand Framework

Reaction of [Au­(C6F5)­(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine
(terpy) leads to complex [Au­(C6F5)­(η1-terpy)] (1). The chemical oxidation of complex
(1) with 2 equiv of [N­(C6H4Br-4)3]­(PF6) or using electrosynthetic techniques
affords the Au­(III) complex [Au­(C6F5)­(η3-terpy)]­(PF6)2 (2). The X-ray diffraction study of complex 2 reveals
that the terpyridine acts as tridentate chelate ligand, which leads
to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal
(gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or
exciplex formation. Time-dependent density functional theory calculations
match the experimental absorption spectra of the synthesized complexes.
In order to further probe the frontier orbitals of both complexes
and study their redox behavior, each compound was separately characterized
using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical
synthesis of complex 2.