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Metal Complexes with Macrocyclic Ligands, V . Formation and dissociation kinetics of the pentaco‐ordinated Ni 2+ , Cu 2+ , Co 2+ and Zn 2+ complexes with 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane
Author(s) -
Hertli Liselotte,
Kaden Thomas A.
Publication year - 1974
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.19740570509
Subject(s) - chemistry , dissociation (chemistry) , kinetics , reaction rate constant , metal , inorganic chemistry , dissociation constant , dissociation rate , rate determining step , ion , medicinal chemistry , crystallography , stereochemistry , catalysis , organic chemistry , receptor , biochemistry , physics , quantum mechanics
The formation and dissociation kinetics of the pentaco‐ordinated Cu 2+ , Ni 2+ , Co 2+ and Zn 2+ complexes with 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (4‐MeCyclam‐14) was studied by pH‐stat techniques and spectrophotometrically. The rates of the reactions between 4‐MeCyclam‐14 and each of the four metal ions, although slower than normal complexations by a factor of 10 3 −10 4 , closely follow the order Cu 2+ > Zn 2+ > Co 2+ > Ni 2+ , found for the rate of water exchange. This implies that beside water exchange an other constant factor plays an important role in the rate determing step. The dissociation of the pentaco‐ordinated 4‐MeCyclam‐14 complexes is acid catalyzed. The limiting rate for acid dissociation is not reached even in 2.5 M HNO 3 in the case of Ni(4‐MeCyclam‐14) 2+ . From the formation and dissociation rates stability constants have been calculated, which do not show any macrocyclic effect.