The kinetics of the formation of the NiII‐complex with 1,4,8,11 ‐tetraazacyclotetradecan (Cyclam) are studied by spectrophotometric and potentiostatic methods. The reaction of Ni2+ with the cyclic ligand is about 30000 times slower than with the open chain triethylenetetraamine (Trien). Therefore the rate determining step with Cyclam can not be the dissociation of the first coordinated water molecule, as it is usually in complexation reactions, but it must be the formation of the second coordinative bond. This is considered to be due to the more rigid structure of Cyclam in comparison with Trien.
Suvnmary. The interaction between Cu2+ and the terdentate ligands N-picolinoyl-ethylenediamine, glycine-2-pyridylmethylamide, Na-(Z-pyridylmethyl)-glycinamide and Na-(Z-pyridylmethyl)-glycine-ethylamide, respectively, has been studied by spectrophotometry and potentiomctry. At high pH values the ionised amide group undergoes complex formation and the resulting chclates have similar structures and stabilities. In slightly acidic solution however, each ligand gives rise to a different species. These facts are explaincd by assuming that the neutral amide group coordinates through its carbonyl oxygen atom. The stability constant and the absorption spectrum of each complex have been calculated by computer programmes.Rontgen-Strukturanalysen zeigen, dass Amide mit Cu2+ und anderen d-MetallIonen zwei Arten von Komplexen bilden, indem entweder der Carbonylsauerstoff sein Elektronenpaar zur Verfugung stellt (I) oder das Stickstoffatorn der deprotonierten Amidgruppe gebunden wird (11) [l]
Surnrnavy. The protonation and deprotonation rates of the coordinated amide group in the Cu2+ complexes with Na-(2-pyridyl-methyl)-glycinamide (I) and N"-(Z-pyridyl-methyl)-glycineethylamide (11) have been studied by stopped flow techniques. It is shown that the rate determining step of the formation of the complex with the deprotonated amide group is given by the rate of water dissociation from Cu2+. Weaker bases than OH .-or stronger acids than water can react by a different path, in which the proton transfer and/or the rotation from the 0-co-ordinated into the N-co-ordinsted form and vice vevsa is rate determining.In aqueous solution amides form two different types of complexes with heavy metal ions. The neutral amide group is bound through its carbonyl oxygen [ Z ] , whereas the deprotonated group co-ordinates via the nitrogen atom as in (1) [ 3 ] .-
Summary. By potentiometry and spectrophotometry Cuz+ and N-(2-dimethylaminoethy1)-oxamide are shown to form different mononuclear complexes and a binuclear species containing a hydroxo bridge. Visible absorption spectra of each species were obtained by an iterative process and used to assign definite structures to them. Stability constants and concentrations of each complex were calculated from the potentiometric data. The ligand behaves as a tridentate chelating agent, and hydrolysis of one coordinated water molecule predominates over deprotonation of the second amid group.
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