Cobalt-59 Nuclear Magnetic Resonance Study of Cobalt(III) Complexes. Empirical Rules for the Cobalt-59 Chemical Shifts and Line Widths of [CoIII(en)<i>x</i>(NH3)6−2<i>x</i>−<i>y</i>L<i>y</i>]-type Complexes

Abstract

Abstract The cobalt-59 chemical shifts and line widths for about seventy cobalt(III) complexes of the [CoIII(en)x(NH3)6−2x−yLy] (L= Cl, Br, NO2, N3, OH, H2O, CO3, and C2O4) type have been measured. The cobalt-59 chemical shifts of this type of complex are approximately represented by a simple relation: δ(ppm)=360x+\oversety\underseti=1∑δ_i(L) (x=0, 1, and 2), where δi(L) is the i-th ligand shift parameter which represents the contribution of the i-th ligand, l, to the total chemical shift. Three empirical rules can be derived from experimental observations: I. The chemical shift of a trans-isomer is higher than that of the corresponding cis-isomer. II. The line width of the trans-CoA4B2 isomer is larger than that of the cis-CoA4B2 isomer. III. The line width of a meridional isomer is larger than that of the corresponding facial isomer. Illustrative examples are presented where cobalt-59 NMR is used to identify cobalt (III) complexes and to study the kinetics and equilibrium in solution.