Au–Au Chemical Bonding in Nitronyl Nitroxide Gold(I) Derivatives

Gold­(I) derivatives of nitronyl nitroxide (NN) stabilized by complexation with phosphine ligands were designed to promote dimerization of the paramagnets in the solid state via Au–Au bonding. The complexes were successfully synthesized by the reaction of the corresponding phosphine [n-Bu3P or (4-FC6H4)3P], AuCl­(THT), and NN–H under basic conditions in high yields. The gold­(I) complexes were characterized by cyclic voltammetry, electron spin resonance, infrared, and UV/vis spectroscopy supported by quantum chemical calculations. Crystallographic analyses of the complexes showed that they possess Au–Au bonds (2.930 and 3.095 Å). The Au–Au bonding was confirmed by density functional theory calculations and quantum theory of “atoms in molecules” and natural bond orbital analyses, which made it possible to determine bond critical points (3, −1) and Au–Au bond orders (0.36 and 0.23) as well as to estimate the orbital contribution to the energy of Au–Au bonds (12.0 and 8.6 kcal/mol).