Syntheses and structural characterization of pyridyldicarboxamide-based multinuclear copper(II) complexes

Derivatives of 1,3,4-thiadiazoles exhibit a several applications in the chemical, pharmaceutical and agrochemical industries1. The pyridine carboxamide derivatives as ligands provide several N- and O-donor sites. This fact make them attractive for the preparation of polynuclear complexes with novel structural topologies2. Such ligands in their deprotonated form generate a pincer cavity via two N-amidate groups and an anchoring pyridine ring that strongly hold a metal ion, while the thiadiazole groups are positioned to create a secondary coordination sphere3. Considering these aspects, we decided to prepare a ligand which contains a 2,6-dicarbonilpyridine ring and 5-(methylthio)-1,3,4-thiadiazole (H2L) for the preparation of multinuclear CuII complexes. The ligand was confirmed through infrared spectroscopy, single-crystal X-ray diffraction and 13C and 1H NMR. Complexes {[Cu4(µ3-OH)2(µ2-Cl)2(L)2]·2DMF} (1) and {[Cu5(µ3-OH)2(L)3(Lb)(dmf)]·DMF·H2O} (2) were obtained in N,N-dimethylformamide (DMF) solution in presence of triethylamine. In complex 2 one of the ligands suffered partial hydrolysis in the amide group, [Lb]2‒. The single-crystal X-ray structures of 1 and 2 show that each copper(II) centre is five-coordinated in an approximately square pyramidal geometry.