FITTING OF NICKEL(II) ION INTO THE 2 14-MEMBERED TETRAAZA MACROCYCLES - BLUE-TO-YELLOW CONVERSION AND THE OXIDATION AND REDUCTION BEHAVIOR

The novel saturated tetraaza macrocycle isocyclam (2) has been synthesized and the behavior of its nickel(II) complexes, which contain a 5, 5, 6, 6 sequence of chelate rings, is compared with that of corresponding complexes of cyclam (1) (sequence: 5, 6, 5, 6). These complexes exist in solution as a mixture of blue, octahedral, high-spin and yellow, planar, low-spin species; the thermodynamic parameters for the blue-to-yellow conversion depend upon the cyclic nature of the ligand. In analogy with Ni(cyclam)2+, Ni(isocyclam)2+ undergoes one-electron oxidation and reduction processes at a platinum electrode in acetonitrile. The easier reduction and more difficult oxidation of both blue and yellow 5, 5, 6, 6 complexes with respect to the 5, 6, 5, 6 analogues have been related to the differences in the in-plane Ni-N interaction parameters, as inferred from electronic spectra. General redox behavior of Ni(II) complexes with tetraaza macrocycles has been reconsidered and a linear correlation between oxidation and reduction potentials is presented. © 1979, American Chemical Society. All rights reserved.