This thesis is concerned with an investigation of the thermodynamic parameters of complexation of the calix[4]pyrrole ligands with anionic substrates, and aims to synthesize modified calix[4]pyrrole ligands with selective affinity towards a specific range of anions. From the 1H NMR studies on calix[4]pyrrole and anions in CD3CN at 298 K the pyrrolic protons are the active site of interaction of this ligand and anions. According to the spectra in CD3CN it can be inferred that the calix[4]pyrrole ligands (CP(I) and CP(II)) show selectivity to fluoride over chloride, bromide and iodide ions. This is reflected in the highest chemical shift observed for the pyrrolic protons of this ligand in its complexation with fluoride. Conductometric measurements in solution were carried out to determine the composition of all the ligand-anion complexes. Thermodynamic parameters of complexation of calix[4]pyrrole ligands and anions of interest (as tetra-n-butylammonium salts) reveal the following selectivity trends in acetonitrile at 298.15 K. CP(I) F > H2PO4- ~ Cl > Br- > I. CP(II) F > H2PO4- ~ Cl > Br-. CP(III) F > H2PO4- (DMF) CP(IV)-ααββ H2PO4- > F > Cl > Br-. CP(IV)-αβαβ H2PO4- ~F > Cl > Br-. The enthalpies of solution for the reactants (both CP(I) and CP(II)) and the product were determined calorimetrically in acetonitrile, N,N-dimethylformamide and benzonitrile for CP(I) and its fluoride, chloride and dihydrogen phosphate complexes. In a similar way, enthalpies of solution of CP(II) and its complexes (fluoride and dihydrogen phosphate) in acetonitrile and N,N-dimethylformamide were determined at 298.15 K. The enthalpies of coordination for both complexes (fluoride and dihydrogen phosphate) were then calculated in both solvents and good agreement was found. Final conclusions and suggestions for further research in this area are given.