UNUSUAL COMPLEXATION BEHAVIOR OF METALLOMACROCYCLES BASED ON ISOTHIOSEMICARBAZIDES WITH RESPECT TO ALKALI AND ALKALINE-EARTH METAL-IONS - NOVEL 2 1 ASSOCIATES/

The reactions between alkali and alkaline earth metal ions and nickel( II) macrocycles based on S-alkylated isothiosemi-carbazides with diffe rent crown ether cavity size were studied in propylene carbonate by sp ectrophotometric and calorimetric titrations. Metallomacrocycles 1 and 2 exhibit normal behavior on 1:1 complexation with alkali- and alkali ne earth metal ions and resemble in this respect 15C5 and 18C6, respec tively. The most stable complexes are formed by these ''ligands'' when the diameter of the cation and the crown ether hole have approximatel y the same size. The most striking feature of the complexation process es studied is the formation of 1:2 metal-ligand associates even in the case of the smallest cations. These associates are very different fro m ''normal'' crown ether sandwich complexes. In reality, the particle formed is an associate between a 1:1 complex, in which the correspondi ng metal ion is well accommodated inside the ligand cavity, and a seco nd metallomacrocyclic Ligand. Their formation is disfavored by enthalp ic contributions. A special kind of ''switch'' from these associates t o normal sandwich complexes takes place in the case of 1, when the cat ion diameter compared to hole size increases. The macrocycle 2 forms t his kind of associates with all akali and alkaline earth ions.