Very Short Metallophilic Interactions Induced by Three-Center–Two-Electron Perhalophenyl Ligands in Phosphorescent Au–Cu Complexes

The synthesis, structural characterization, and study
of the photoluminescent
properties of the complexes [Au3Cu­(C6F5)4(NCCHCHPh)3]n (1) and [Au2Cu­(C6Cl5)3(NCCHCHPh)2] (2) have been carried out. The crystal structures
of complexes 1 and 2 display a common [Au2Cu­(C6X5)2(μ-C6X5)­(NCCHCHPh)2] fragment built up through a
trinuclear Au2Cu unit with a perhalophenyl group acting
as a three-center–two-electron bridging ligand. In the case
of 1 an additional [Au­(C6F5)­(NCCHCHPh)]
unit is also present in the asymmetric unit. Both complexes are brightly
luminescent in the solid state at room temperature and at 77 K with
lifetimes in the nanosecond range for 1 and in the microsecond
range for 2. The presence of very short metallophilic
interactions seems to be responsible for the low-energy luminescence
observed. DFT and time-dependent DFT calculations agree with the experimental
results and support the idea of that the origin of the emissions arises
from metal-based orbitals and arrive at ligand-based orbitals as charge
transfer transitions.