Stability and ESR spectra of Ni(III) tetraazamacrocyclic complexes in nitrate and chloride solutions

Complexes [Ni-III(cyclam)Cl-2]Cl (1), [Ni-III(cyclam)(NO3)(2)]ClO4 (2) and [Ni-III(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 an d NaNO3 concentration. In complexes 2 and 3 the decay of Ni(III) followed t he first order kinetics in aqueous and in nitrate solutions up to 1 mol/dm( 3). In complex 1 the first order kinetics was observed only in aqueous and saturated NaCl solutions. With increase in NaNO3 concentration the stabilit y of Ni(III) in complexes 2 and 3 increased however, in complex 3 it was lo wer than in complex 2. Stability of Ni(III) in complex 1 increased also wit h increasing NaCl concentration but it diminished starting from 2 mol/dm(3) NaCl. The forms of complexes depending on the salt concentration were char acterized by the ESR technique.