THE MEDIUM EFFECT ON THE THERMODYNAMICS OF COMPLEXATION OF HOXY)-26,28-BIS[(DIETHYLAMINE)ETHOXY]CALIX(4)ARENE AND THE SILVER CATION

The interaction of 27-bis(methylthioethoxy)-26,28-bis[(diethylamine)- ethoxy]calix(4)arene and the silver cation was investigated by H-1 NMR in CD3OD and CD3CN at 298 K. The results suggest that the hydrophilic cavity of the ligand hosts the metal cation through interaction with the different donor atoms (O, N, S). Conductometric titrations of Agand this ligand in methanol and in ethanol indicate that the stoichiom etry of the metal ion-ligand complex is 1:1. The thermodynamics of com plexation of 1a and silver in six different solvents (methanol, ethano l, propan-1-ol, N,N-dimethylformamide, acetonitrile, and benzonitrile) at 298.15 K was derived from titration calorimetry. Stability constan ts were also checked by direct potentiometry using silver electrodes. Standard Gibbs energies of solution of 5,11,17,23-tetrakis(1, methylet hyl)-25,27-bis(methylthioethoxy)-26,28-bis [(diethylamine)ethoxy]calix (4)arene derived from solubility measurements in different solvents ar e used to calculate transfer Gibbs energies from acetonitrile to vario us solvents. The medium effect on the complexation process is assessed in terms of Gibbs energies taking into account the differences in sol vation of the free and the complex metal cation and the ligand in the appropriate solvents. Representative examples are given to demonstrate that the medium alters the stability of the complex in a selective ma nner which is dependent upon the solvation changes that the reactants and the product undergo upon complexation in the various solvents.