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Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Polyamines, in Relation with the Chelate Effect
Author(s) -
Delville Alfred,
Detellier Christian,
Gerstmans André,
Laszlo Pierre
Publication year - 1981
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19810640219
Subject(s) - chemistry , chelation , denticity , solvation , diamine , tetrahydrofuran , diethylenetriamine , ethylene diamine , molecule , amine gas treating , inorganic chemistry , crystallography , organic chemistry , solvent , crystal structure , nuclear chemistry
The problem of determining the chelate effect brushes against methodological snags: the choice of concentration units, and of the appropriate standard states. We avoid these pitfalls by defining the chelate effect from measurements on bidentate ligands alone, without recourse to comparison with the corresponding unidentate ligands. Quantitation of the parameters extracted from the data is effected by three independent and mutually consistent procedures. Solvation of the Na + ‐cation by the polyamines follows the sequence: cadaverin < 1, 3‐diaminopropane ≪ ethylene diamine ≪ diethylenetriamine. Entry of the first and of the second diamine molecule into the sodium coordination shell are independent and equiprobable steps: K 1 = K 3 and K 2 = K 4 , within the accuracy of the measurements. For ethylene diamine, the values of K 1 and K 3 are in the range 1.0–1.5 and those for K 2 and K 4 are in the range 83–102: attachment of the second N‐atom is considerably easier, by two orders of magnitude (chelate effect). The chelate effect is strongly reduced in cadaverin, with a longer hydrocarbon chain connecting the two amine functions.