Inorganic cation complexes with macrocyclic ligands have been intensively examined during the last decades. It has been found that the selectivity of complexation in solution depend not only on the ratio of the diameters of the cation and the crown ether cavity, but also on the solvating ability of the solvent with respect to the cation and the complex. However, the studies on the influence of solvent on formation of the crown ether-cation complexes are little, particularly in the mixed solvents. In this work, we report a study of interaction between NH4+ ion 1,4,10-trioxa-7,13-diaza cyclopentadecane (DA15C5), n-Phenylaza-15-crown-5(NPA15C5), 18-Crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6),4', 4"(5") ditertbutyl-dicyclohexano-18-crown-6 (t-bu)2DC18C6, dibenzo-21-crown-7(DB21C7) in different percent of dimethylsulfoxide-acetonitrile solvent mixture at various temperature. Formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data and in the case of ammonium found to decrease with increasing mole fraction of dimethylsulfoxide, 100% AN > 90% AN > 80%. In study of the effect of ligand structure, it was found that constant formation will vary in the order of, DA15C5 > DC18C6 > 18C6 > (t-bu)2DC18C6 > DB21C7 > NPA15C5. The enthalpy and entropy of the complexation reactions were determined from the temperature dependence of the formation constants. References: [1] C.J. Pedersen, J.Am.Chem.Soc.,1967, 89, 2495 [2] C. J. Pedersen.,Ibid., 1967, 89,7017 [3] F. Vogtle, H. Sieger, W. M. Muller, Top. Curr Chem.m 1981, 98, 107 [4] L. F. Lindoy " The Chemistry of Macrocyclic Ligand Complexes" Cambridge University Press. Cambridge, New York. Orchester, 1981. P.1
