Complexation study of 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (kryptofix 22DD) with the Co2+, Cr3+, Tl+, and UO2 2+ 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 (ΔSc0, ΔHc0) 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.