SPECTROPHOTOMETRIC STUDY OF SOME ALKALI AND ALKALINE-EARTH CRYPTATES IN DIMETHYLFORMAMIDE SOLUTION USING MUREXIDE AS A METALLOCHROMIC INDICATOR

The complexation of some alkali and alkaline earth cations by cryptands C222, C221, C211, C111, C22 and C21 has been studied in dimethylformamide solution by means of a competitive spectrophotometric technique using murexide as a metal ion indicator. In most cases, a pronounced "cryptate effect" was observed for bicyclic cryptates over corresponding monocyclic complexes which was characterized by high selectivity and high stability. The origin of the stability sequences is discussed in terms of the ligand structural properties. Optimal fit of the cation into the intramolecular cavity of cryptands agrees well with the observed selectivities of the resulting cryptates; Ba2+ and K+ with C222, Sr2+, Ca2+ and Na+ with C221 and Li+ with C211 form the most stable complexes in the series.