Conductometric Determination of the Stability Constants of the Inclusion Complexes of Alkali Cations with [22-DD] Diaza Crown Ether,[211] and [221] Cryptands in Acetonitrile

摘要

An equilibrium study concerning the association of Na~+,K~+,Rb~+ and Cs~+ with 4,7,13,18-tetraoxa-l,10-diazabicyclo [8,5,5]-eicosane [211],4,7,13,16,21-pentaoxa-l,10-diazabicyclo [8,8,5]-tricosane [221] and 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane [22-DD] in acetonitrile has been carried out at 25 deg C by using a conductometric technique.The observed molar conductivity,A,of a test solution was found to decrease significantly for mole ratios less than 1:1 upon the addition of the complexing ligand.A model based on 1:1 stoichiometry has been used to analyze the conductivity data.The data have been fitted according to a non-linear least-squares analysis that provides the stability constant,K,and the molar conductivity,LAMBDA_c,for each cation-ligand inclusion complex.The binding sequences were found to follow the order:Na~+ > K~+ > Rb~+ > Cs~+(Kapprox= 0)for [211],Na~+ > K~+ > Rb~+ > Cs~+ for [221] and K~+ > Na~+ > Rb~+ > Cs~+ for [22-DD] complexes.Trends in ionic conductivities of complexed ions are also discussed.