REDUCTION POTENTIALS OF TETRAAMINECOPPER(II I) COUPLES/

`The difference in steric strain between the oxidized and the reduced forms of tetraaminecopper complexes is correlated with the correspondi ng reduction potentials. The experimentally determined data considered range from -0.54 to -0.04 V (vs. NHE) in aqueous solution and from -0 .35 to -0.08 V (vs. NHE) in MeCN. The observed and/or computed geometr ies of the tetraaminecopper(II) complexes are distorted octahedral or square-pyramidal (4 + 2 or 4 + 1) with (distorted) square-planar CuN4 chromophores (Cu-II-N = 1.99-2.06 Angstrom; Cu-O-4+2(Ax) approximate t o 2.5 Angstrom; Cu-O-4+1(ax) approximate to 2.3 Angstrom), those of th e tetraaminecopper(I) complexes are (distorted) tetrahedral (four-coor dinate; Cu-I-N = 2.12-2.26 Angstrom; tetrahedral twist angle empty set = 30-90 degrees). The reduction potentials of Cu-II/I couples with pr imary-amine ligands and those with macrocyclic secondary-amine ligands were correlated separately with the corresponding strain energies, le ading to slopes of 70 and 61 kJ mol(-1) V-1, with correlation coeffici ents of 0.89 and 0.91, respectively. The approximations of the model ( entropy, solvation, electronic factors) and the limits of applicabilit y are discussed in detail and in relation to other approaches to compu te reduction potentials of transition-metal compounds.