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

Reaction of [Au2Ag2R4­(Et2O)2] (R = C6Cl2F3– or C6F5–) with [Pb­{HB­(pz)3}]Cl in a 1:2 molar ratio led to complexes [AuPb­{HB­(pz)3}­R2] (R = C6Cl2F3– (2) or C6F5– (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)3}­Au­(C6Cl5)2] (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.