Electrochemical and spectroscopic studies of metal cyclam complexes with thiocyanate. Evidence for mixed ligand complex formation

摘要

Complexes of Ni~II, Co~II containing the macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane (cyclam), and their ability to form mixed ligand complexes with thiocyanate have been studied. These complexes in a 1:2 mole ratio, exhibit new absorption peaks at 450, 538 and 512 nm respectively. Addition of thiocyanate to the nickel-cyclam complex (1:2:5 mole ratio) led to the formation of a purple complex, exhibiting three distinct new absorption peaks at 330, 455 and 662 nm. A purple complex (1:2:10 mole ratio) separated, having absorption peaks at 352, 503 and 693 nm in CHCl_3. The Co~II-cyclam complex with thiocyanate in the same mole ratio exhibits two absorption peaks at 437 and 519 nm without appearance of any precipitate. The Cu~II-cyclam complex with thiocyanate did not form a mixed ligand complex. Electrochemical studies also confirmed the complex formation of Ni~II-cyclam with the thiocyanate with the appearance of two new oxidation poeaks close to 1.25 and 1.60 V versus Ag/AgCl in H_2O and CHCl_3. The Co~II-cyclam complex with thiocyanate exhibited an oxidation peak at 1.2 V versus Ag/AgCl, while no peak was observed for the Cu~II-cyclam complex with thiocyanate. Based on spectroscopic and electrochemical no peak was observed for the Cu~II-cyclam complex with thiocyanate. Based on spectroscopic and electrochemical studies the geometry of the complex has been evaluated.