N-bonding vs. S-bonding in thiocyanato-copper(II) complexes

Three mononuclear thiocyanato-Cu(II) complexes have been synthesized: the mono-thiocyanato [Cu(cyclen-tpam)(NCS)]ClO4·3H2O (1) and [Cu(DPA)(NCS)ClO4] (2), and the dithiocyanato complex Cu(bdmpzpy)(NCS)2 (3), where cyclen-tpam = 1,4,7,10-tetrakis(propionamide)-1,4,7,10-tetraazacyclododecane, DPA = bis(2-pyridylmethyl)amine, and bdmpzpy = 2,6-bis[(2,5-dimethyl-1-pyrazolyl)methyl]pyridine. The single crystal X-ray crystallography of the complexes confirmed the perfect square pyramidal geometry (SP) in 1 and distorted SP geometry in 2 and 3 with N-bonding coordination mode for the thiocyanato ligands. The IR spectra of the complexes which were consistent with the N-bonding coordination mode of the thiocyanate group(s) and the visible spectra which revealed the square pyramidal geometry around the central Cu2+ ion were in complete agreement with the X-ray structural determination.