Synthesis, crystal structure and electrochemistry of cobalt(III) carboxamide complexes with amine and azide ancillary ligands

Six cobalt(III) complexes of the type [CoIII(Me2bpb)(amine)(N3)] {Me2bpb2− = N,N′-(4,5-dimethyl-1,2-phenylene)dipicolinamide and amine = piperidine (pprdn) (1), pyrrolidine (prldn) (2), morpholine (mrpln) (3), pyridine (py) (4), 4-methylpyridine(4-Mepy) (5) and 4-acetylpyridine (4-Acpy) (6)} have been synthesized and characterized by elemental analyses, IR and UV–Vis spectroscopy. The structures of 1, 3 and 4 have been determined by X-ray crystallography. Me2bpb2− is a dianionic tetradentate ligand, furnishing a N4 set, such that two N atoms of the two pyridine rings and two amido N atoms occupy four equatorial positions. The amine and azide ligands occupy the two axial positions, leading to a distorted octahedral geometry around the central cobalt ion. The electrochemical behavior of these complexes in DMF solution indicates that partial solvolysis of the complexes occurs and the axial amine ligand is replaced by DMF solvent in 1–6 leading to a [CoIII(Me2bpb)(DMF)(N3)] species. The two additional redox processes observed in the cyclic voltammograms of these complexes originate from the oxidation of the 4,5-dimethylorthophenylene moiety of the Me2bpb2− ligand and a CoIII/II redox process in [CoIII(Me2bpb)(DMF)(N3)]. The CoIII/II redox potential of the [CoIII(Me2bpb)(amine)(N3)] complexes is influenced by the nature of the axial amine ligand and varies from −0.53 for 4-Acpy to −0.79 V for pyrrolidine.

Graphical abstractA series of cobalt(III) complexes with the dipicolinamide ligand H2Me2bpb, prepared by an environmentally benign method, has been synthesized and fully characterized. The X-ray crystal structures of the trans-[CoIII(Me2bpb)(amine)(N3)] complexes with amine = piperidine, morpholine and pyridine have been determined. Spectral and electrochemical studies are also reported.Figure optionsDownload full-size imageDownload as PowerPoint slide