Synthesis, characterization, and electrochemistry of SNS cobalt(II) tridentate complexes

The preparation of two cobalt(II) complexes that contain a tridentate ligand with sulfur, nitrogen, and sulfur donor atoms is described. The tridentate ligand precursors are based on bis-imidazole or bis-triazole moieties. The complex based on a bis-imidazole precursor was green in color and was prepared in 93.3% yield. The complex based on a bis-triazole precursor was blue-green in color and was prepared in 69.8% yield. Single-crystal structures of both complexes were obtained. Both complexes contain [BF 4 ] − as the counter-anion. Based on the single-crystal structure, the molecular geometry around the cobalt(II) center is distorted tetrahedral. EPR spectra were obtained for both complexes at 4 K. Each complex has axial symmetry for its electron density and each cobalt(II) complex has S = 3/2. For the complex based on a bis-imidazole precursor, the UV–Vis peaks were observed at 696 nm, 629 nm, 585 (sh) nm, and 375 (sh) nm. For the complex based on bis-triazole, UV–Vis peaks were observed at 681, 613, 570, 243, 239, 236, 233, 230, 227, and 210 nm. Cyclic voltammetry spectra were obtained for both complexes. Both the ligand precursor and the cobalt(II) complexes are redox active. All of the redox waves were irreversible.