Abstract
A general review on macrocyclic ligands with particular emphasis to dibenzocryptand 222 and dibenzo 18 crown 6 is given in the first part of the thesis (Chapter 1). This is followed by an exhaustive literature survey on the stability constants (hence free energies of complexing), enthalpies and entropies of metal cations with cryptands (dibenzocryptand 222, benzocryptand 222, cryptand 222) and crown ethers (dibenzo 18 crown 6, benzo 18 crown 6, 18 crown 6) in water and in non-aqueous solvents at 298.15 (Chapter 2). The experimental part (Chapter 3) also includes a detailed description of the principals involved in calorimetry as well as the methods used for the calculation of reaction enthalpies. Stability constant data for alkali-metal and silver cations with dibenzocryptand 222 in five dipolar aprotic solvents (N,N dimethyl-formamide, dimethylsulphoxide, acetonitrile, propylene carbonate and nitromethane) at 298.15 K are reported. These data are used to calculate the standard free energies of the complexation process involving metal(I) cations and dibenzocryptand 222 in the dipolar aprotic solvents. Free energy data are combined with enthalpy data obtained in this work in order to evaluate the entropies of complexation of these cations with dibenzocryptand 222 in these solvents. A linear correlation previously shown for metal(I) cations and cryptand 222 in DMF, Me2SO, AN, PC and NM between entropies of complexing and entropies of solvation of metal(I) cations in dipolar aprotic solvents is also found for dibenzocryptand 222. The results obtained in this thesis provide further evidence that the complexation process with metal (I) cations and cryptands is mainly controlled by the state of solvation of the cation in the solvent. Enthalpies of solution of dibenzocryptand 222 in the dipolar aprotic solvents are reported and the thermodynamic parameters for the extraction process in the water + nitromethane solvent system as described by M+(H2O) + 22B2B(NM) → M+22B2B (NM) are calculated (Chapter 4). Thermodynamic parameters of solution and transfer of dibenzo 18 crown 6 are discussed with respect to corresponding data for dibenzocryptand 222. The transfer free energies of metal ion dibenzocoronates from water to a number of solvents are calculated and it is shown that, unlike cryptates, there is an interaction between the complexed cation and the solvent in metal ion dibenzocoronates in dipolar aprotic media. Thermodynamic parameters of complexation for alkali-metal and dibenzo 18 crown 6 in acetonitrile are reported. The complexation process seems to be enthalpically and entropically controlled (Chapter 5). Synthesis of crown compounds and heats of solution of 18 crown 6 carried out at several temperatures as well as DeltaCp values in water are presented in Chapter 6.