Nitric oxide reduction of copper(II) complex with tetradentate amine ligand followed by ligand transformation

Copper(II) complex 1 with a tetradentate ligand L [L = tris(2-aminoethyl)amine, tren] has been prepared as its perchlorate salt. Single crystal X-ray structure of 1 indicates its trigonal bipyramidal shape in the solid state. The complex, in dry and degassed acetonitrile solvent, was made to react with nitric oxide gas and the copper(II) center has been observed to reduce to Cu(I) with simultaneous nitrosation followed by diazotization at the terminal primary amine positions of the ligand to result into cyclization product, 1-(2-aminoethyl)piperzine, L′ along with tris(2-aminoethyl)ammonium perchlorate, L′′-perchlorate. However, when an acetonitrile:water (10:1, v/v) mixture has been used as the solvent, the reduction of Cu(II) to Cu(I) is observed and the ligand is found to be precipitated out only as L′′-perchlorate. The reduction of Cu(II) to Cu(I) has been studied by UV–visible, 1H NMR and EPR spectroscopic techniques and by X-ray single crystal structure determination. Both the L′ and L′′-perchlorate have been isolated from the reaction mixture and characterized by using microanalytical studies, various spectroscopic techniques and X-ray single crystal structure determination.