Studies involving mixed-donor macrocyclic ligands. A comparative study of the influence of medium effects on the stabilities of complexes of CoII, NiII, and CuII with 14- to 16-membered O2N2-donor macrocycles

Abstract

The effect of change of background electrolyte and solvent from 95% methanol (I= 0.1 mol dm^–3, NEt₄ClO₄ or NMe₄Cl) to 65% ethanol (I= 0.1 mol dm^–3, NMe₄NO₃) on the stability constants of a series of complexes of Co^II, Ni^II, and Cu^II with 14- to 16-membered O₂N₂-macrocycles has been investigated. The present study does not substantiate the results of a previous study, in which the latter conditions were employed, when it was proposed that a different stability order occurs for the complexes of the 14- and 16-membered macrocycles than reported for these complexes in 95% methanol (I= 0.1 mol dm^–3, NMe₄Cl). Instead, it was found that the same stability order is maintained no matter which of the above conditions is employed for the measurements. In the case of the nickel(II) complexes, the stability increases from the 14- to the 16-membered ring in accordance with the previous prediction that the fit of the latter ring is nearly ideal for high-spin Ni^II.