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Unusual Complexation Behavior of Metallomacrocycles Based on Isothiosemicarbazides with Respect to Alkali and Alkaline Earth Metal Ions: Novel 2:1 Associates
Author(s) -
Reetz Manfred T.,
Arion Vladimir B.,
Trültzsch Rainer,
Buschmann HansJürgen,
Cleve Ernst
Publication year - 1995
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19951281106
Subject(s) - chemistry , alkali metal , alkaline earth metal , crown ether , ligand (biochemistry) , inorganic chemistry , metal , titration , ether , metal ions in aqueous solution , propylene carbonate , ion , crystallography , polymer chemistry , organic chemistry , electrolyte , biochemistry , receptor , electrode
The reactions between alkali and alkaline earth metal ions and nickel(II) macrocycles based on S ‐alkylated isothiosemi‐carbazides with different crown ether cavity size were studied in propylene carbonate by spectrophotometric and calorimetric titrations. Metallomacrocycles 1 and 2 exhibit normal behavior on 1:1 complexation with alkali‐ and alkaline earth metal ions and resemble in this respect 15C5 and 18C6, respectively. The most stable complexes are formed by these “ligands” when the diameter of the cation and the crown ether hole have approximately the same size. The most striking feature of the complexation processes studied is the formation of 1:2 metal‐ligand associates even in the case of the smallest cations. These associates are very different from “normal” crown ether sandwich complexes. In reality, the particle formed is an associate between a 1:1 complex, in which the corresponding metal ion is well accommdated inside the ligand cavity, and a second metallomacrocyclic ligand. Their formation is disfavored by enthalpic contributions. A special kind of “switch” from these associates to normal sandwich complexes takes place in the case of 1 , when the cation diameter compared to hole size increases. The macrocycle 2 forms this kind of associates with all akali and alkaline earth ions.