Abstract
An introduction is given regarding the chemistry and applications of lanthanide complexes. Subsequently, an account is presented on the complexation chemistry of macrocycles and trivalent cations. Thus, it follows that the primary aim of this work is to proceed with a systematic investigation of the complexation chemistry between the trivalent cations (Ln3+) and different macrocycles in two dipolar aprotic solvents (acetonitrile and N, N-dimethylformamide). The investigated macrocycles are, {tetrakis[4-(ethyl) morpholine] oxyl}-p-tert-buty lcalix[4] arene (L1), (tetrakis[1-(ethyl)piperidine] oxyl} -p-tert-butylcalix[4]arene (L2), {tetrakis [1-(ethyl) methyl ketone] oxyl}-p-tert-butylealix[4]arene (L3), {di-substituted [di-methylcarbamyl] ethoxyl di-hydroxyl}-p-tert-butylcalix[4]arene (L4), {tetrakis [tetra-acetamide] oxyl}-p-tert-butylcalix[4]arene (L5), {di-substituted [acetylurethane] oxy dihydroxy}-p-tert-butylcalix[4]arene (L6), {di-[ethyl-phosphate amino]oxyl di-hydroxyl}-p- tert-butylcalix[4]arene (L7) and cryptand 222. This investigation was accomplished through 1H-NMR, conductimetric, potentiometric, UV-spectrophotometric and microcalorimetric titration studies in these solvents at the standard temperature. In general, 1H-NMR titrations in deuterated acetonitrile at 298 K concluded that the active sites of interaction in these ligands with trivalent cations are mainly assigned to the oxygen and to a lesser extent to the nitrogen donor atoms. Conductimetric titration data in acetonitrile at 298.15 K suggested the formation of 1:1 [L]/[M] complex stoichiometry for all of the investigated systems except for L7 and Ln3+ cations. For these systems microcalorimetric titration studies revealed that the interaction of these cations and L7 in this medium leads to the formation of 2:1 [L]/[M] complexes. Studies performed in N, N-dimethylformamide displayed weak or absence of interaction, which emphasises the effect of the media on the complexation of these cations and these macrocycles. The strength of complexation of L1, L2, L3 and L4 and these cations in acetonitrile at 298.15 K was found to be weak and insignificant selectivity was noticed, while the interaction between L5 and the Ln3+ cations showed relatively strong and selective complexation in acetonitrile and to a lesser extent in N,N-dimethylformamide. The thermodynamic parameters for 2:1 [L7]/[Ln 3+] complexes in acetonitrile revealed an unusual pattern. Moreover, strong and selective interaction between cryptand 222 and the Ln3+ cations in acetonitrile at 298.15 K was found. Finally, conclusions and suggestions for further work are given.