X-RAY CRYSTAL-STRUCTURE OF [NI(III)(CYCLAM)(NO3)2](CLO4) AND ELECTRON-TRANSFER REACTIONS OF THE NI(III)/NI(II) COUPLE

The synthesis and crystal structure of [Ni(cyclam)(NO3)2](ClO4) are described (PI, a = 8.347(4) angstrom, b = 15.960(7) angstrom, c = 7.656(3) angstrom, alpha = 90.33(6)-degrees, beta = 110.97(4)-degrees, gamma = 104.45(5)-degrees, V = 917.0(7) angstrom3, R = 0.0425, R(w) = 0.0384). The crystal contains two unique Ni(III) cations within the unit cell, with a network of hydrogen bonding interactions linking one of the cations into a stacked configuration while the other cation contains a strong internal hydrogen bond. This provides an interesting inorganic example of multi-site cooperative binding involving a metal complex cation. By use of electron transfer data from known outer-sphere redox reagents, measurement of the cross-reactions with [Ni(cyclam)]3+/2+ in 3 M nitrate media yielded a self-exchange rate constant of 1.4 x 10(5) M-1 s-1. The structural data have been utilized to obtain a calculated estimate of the self-exchange rate constant (1.0 x 10(8) M-1 s-1) for this couple. The relationship between these two values is explored. The lack of adiabaticity is reflected in a value almost-equal-to 0.01 for kappa(el), not only for this couple but also for other related cyclam complexes.