Conductometric study of complexation reaction of 4′-nitrobenzo-15-crown-5 with Mn⁺², Co⁺², Y⁺³, and ZrO⁺² cations in acetonitrile, methanol and their binary solvent solutions

Abstract

The complexation reactions of Mn²⁺, Co²⁺, Y³⁺, and ZrO²⁺ cations with the macrocyclic ligand, 4′-nitrobenz-15-crown-5 (4′-NB15C5), in acetonitrile (AN), methanol and AN-MeOH binary mixtures have been studied at various temperatures using the conductometric method. The conductance data stand for the Me : L stoichiometric ratio 1 : 1. Values of the formation constants of the complexes were accumulated by plotting molar conductivity curves using the computer program, GENPLOT. The order of stability of the metal-ion complexes in pure AN at 15°C was found to be: (4′-NB15C5 · ZrO)²⁺ > (4′-NB15C5 · Mn)²⁺ ≈ (4′-NB15C5 · Co)²⁺ > (4′-NB15C5 · Y)³⁺. In the case of AN-MeOH binary solvent solutions with 50 and 75 mole percent of AN at the same temperature, the sequence of stability of the complexes was the following: (4′-NB15C5 · Mn)²⁺ > (4′-NB15C5 · ZrO)²⁺ ≈ (4′-NB15C5 · Co)²⁺ 〉 (4′-NB15C5 · Y)³⁺, and (4′-NB15C5 · Mn)²⁺ > (4′-NB15C5 · Y)³⁺ ≈ (4′-NB15C5 · Co)²⁺ > (4′-NB15C5 · ZrO)²⁺, respectively. The complexes formed are entropy stabilized in all cases.