Complexation study of 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (kryptofix 22DD) with the Co2+, Cr3+, Tl+, and UO22+ cations in acetonitrile, methanol, and their binary mixtures

Abstract

Complexation between 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (kryptofix 22DD) and the Co²⁺, Cr³⁺, Tl⁺, and UO₂²⁺ cations in acetonitrile, methanol, and their binary mixtures was studied by conductometry at different temperatures. The experimental results showed the formation of 1: 1 [ML] complexes between the studied metal cations and the macrocyclic ligand in most solvent systems. The stability constants of the resulting 1: 1 complexes were determined by computer fitting the conductance–mole ratio data. The stability of the metal–ion complexes in pure acetonitrile at 15 and 25°C was found to decrease in the order: [Tl (kryptofix 22DD)]⁺ > [Co(kryptofix 22DD)²⁺] > [UO₂(kryptofix 22DD)]²⁺. Along with 1: 1 [ML] complexes, 2: 1 [M₂L], 2: 2 [M₂L₂], 2: 3 [M₂L₃], 1: 2 [ML₂], and 1: 3 [ML₃] complexes are likely to be formed in some of the solvent systems. The thermodynamic parameters (ΔS_c⁰, ΔH_c⁰) of the complex formation in the studied nonaqueous solvents, obtained from the temperature dependences of the stability constants of the complexes, showed that the process is athermic.