Investigation of the selective complex forming properties of some calix [4] arene derivatives

Conical calixarenes which have suitable co-ordination spheres are capable of bonding alkali and alkali earth metal ions as well as aliphatic amines. If a sensitive indicator group is bound to macrocyclic skeleton, the complex formation can be easily observed by UV/Vis spectroscopy. Recently. selective complexation reactions are in the focus of interest, because these ligands can be used in optical sensors for the quantitative determination of particular ions in multi-ionic system, such as physiological liquids. In this work four series of compounds with different substituents were investigated. First 7a and c (for structures see the Hungarian text) were studied which contained one hydroxyl and three alkoxy groups in the coordination sphere. They were found to be highly selective to lithium ions in the presence of triethylamine base, however, they are not ideal to measure the concentration of this cation because of their rather low K, equilibrium constants of complex formation (K-c(7a-Li+)=3,4*10(-2) dm(3) mol(-1) and K-c(7c-Li+)=1,6*10(-2) dm(3) mol(-1)). A model for the evalution of K-c is presented [1,2]. In the next series 8a and 8c were synthesized with ethoxycarbonylmethyl groups substituting alkoxy moieties in the coordination sphere. In this case the complexation constant, K-c, is much higher in the presence of triethylamine traces, however, these compounds are capable of binding lithium, sodium and calcium ions quite selectively, so that the selectivity became lower [2]. The structure of the 8c-Li+ complex was observed by H-1 and Li-7 NMR spectroscopy. It is appearent from the results that the lithium ion is bound in the co-ordination sphere, however, the formation of quinodial structure was not detected. T-1 and T-2 relaxation times of Li-7 nuclei decreased markedly due to the complex formation [3]. The selectivity of opened and bridged ligands could be compared via studying 10a and b calixarenes. 10b contained a diamide bridge - and not a crown ether bridge, as usual - which increased the selectivity significantly. Complex formation with aliphatic amines were also found to be selective to primary amines. The stoichiometry complexes formed was also investigated [4]. The cromophoric unit of series 11 was indophenolic group. Ligands with different diamide bridges were compared with the crown ether bridged 11d reported by Kubo et al. The equlibrium constants of complex formation, K-c, was determined systematically with several aliphatic amines in ethanol and DMSO in order to study the effect of substrate on the equilibrium. The effect of solvent polarity was also observed and polar solvents were found to be favourable for the complex formation [5, 3].