DETERMINATION OF COMPLEX STABILITIES WITH NEARLY INSOLUBLE HOST MOLECULES .2. COMPLEXATION OF ALKALI AND ALKALINE-EARTH METAL-CATIONS WITH DIBENZO CROWN-ETHERS IN AQUEOUS-SOLUTION

An experimental method was developed to determine the stability consta nts with nearly insoluble ligands in homogeneous solution. This method was tested using dibenzo crown ethers, which have a very low solubili ty in aqueous solution. The stability constants for the complexation o f alkali and alkaline earth metal cations with different dibenzo crown ethers were determined in aqueous solution. Owing to the complex form ation the total concentration of the ligand in solution increases. Dib enzo crown ethers absorb in the ultraviolet spectral range, hence the increase in the ligand concentration can be easily detected. Without t he knowledge of the molar absorptivities of the ligands and of the cor responding complexes and of the solubilities, the stabilities of the c omplexes formed can be calculated under certain assumptions. To verify these assumptions, the solubilities of the dibenzo crown ethers and t he molar absorptivities were determined. The kinetics of the solubiliz ation process of the ligands was followed by spectrophotometric measur ements. (C) 1997 John Wiley & Sons, Ltd.