New Au(i)-Cu(i) heterometallic complexes: the role of bridging pyridazine ligands in the presence of unsupported metallophilic interactions.

The reaction of the polymers [Au2Cu2(C6X5)4(NCMe)2]n (X = Cl (1), F (2)) with the aromatic N-donor ligand pyridazine in different molar ratios gives rise to new Au(i)/Cu(i) heterometallic complexes [AuCu(C6Cl5)2(μ2-C4H4N2)(NCMe)]2 (3), [AuCu(C6X5)2(μ2-C4H4N2)(C4H4N2)]2 (X = Cl (4), X = F (6)) and [Cu2(μ2-C4H4N2)3(NCMe)2][Au(C6F5)2]2 (5). In all cases, the close proximity of the donor atoms in the diazine ligand leads to discrete molecules where two copper centres are connected by two or three bridging pyridazine ligands. In this way, focusing on the number of bridging ligands present in the molecules, unsupported closed-shell Au(i)Cu(i) (with two bridging pyrazine ligands) or weak Cu(i)Cu(i) interactions (with three bridging pyridazines) have been observed. None of these pyridazine derivatives is luminescent, which is probably related to the absence of aurophilic contacts.