New Insights into the Au(I)···Pb(II) Closed-Shell Interaction: Tuning of the Emissive Properties with the Intermetallic Distance.

Reaction of [AuAgR(EtO)] (R = CClF or CF) with [Pb{HB(pz)}]Cl in a 1:2 molar ratio led to complexes [AuPb{HB(pz)}R] (R = CClF (2) or CF (3)) through transmetalation reactions. The crystal structures of these complexes display unsupported Au(I)···Pb(II) interactions of 3.0954(4) (2) and 3.2778(4) (3) Å, together with one (2) or two (3) F···Pb weak contacts. These intermetallic distances are compared to the shortest one found for the previously reported complex [Pb{HB(pz)}Au(CCl)] (1) of 3.0494(4) (1) Å, showing a clear dependence with the donating properties of the different aurate units. The complexes are emissive in the solid state due to charge transfer transitions associated with the presence of Au(I)···Pb(II) interactions, in which the intermetallic distance plays a crucial role. Density functional theory and time-dependent density functional theory calculations support the assignment of the luminescent properties of the complexes. Ab initio Hartree-Fock and MP2 calculations on model systems of complexes 2 and 3 show the presence of strong Au(I)···Pb(II) closed-shell interactions of an ionic plus dispersive nature together with weak F···Pb contacts of a dispersive origin in the case of complexes 2 and 3.