Stability and ESR Spectra of Ni(III) Tetraazamacrocyclic Complexes in Nitrate and Chloride Solutions

Complexes [NiIII(cyclam)Cl2]Cl (10, NiIII(cyclam)(NO3)2]lO4 (2) and [NiIII(2-methyl-cyclam)(NO3)2]ClO4 (3) were isolated and the stability of Ni(III) was studied by UV-VIS spectrophotometry as a function of NaCl and NaNO3 concentration. In complexes 2 and 3 the decay of Ni(III) followed the first order kinetics in aqueous and nitrate solutions up to 1 ol/dm3. In complex 1 the first order kinetics was observed only in aqueous and saturated NaCl solutions. With increase in NaNO3 concentration the stability of Ni(III) in complexes 2 and 3 increased however, in complex 3 it was lower than in complex 2. Stability of Ni(III) in complex 1 increased also with increasing NaCl concentration but it diminished starting from 2 mol/dm3 NaCl. The forms of complexes depending on the salt concentration were characterized by the ESR technique.