| 摘要: | The stability constants of the nickel(Ⅱ) complexes of 4- methyl- 4, 7- diazadecanediamide (4- Me- L- 2, 2, 2), 4, 7- dimethyl- 4, 7- diazadecanediamide (4, 7- Me2- L- 2, 2, 2), 4 -ethyl- 4, 7- diazadecanediamide (4- Et- L- 2, 2, 2), and 4- methyl- 4, 8- diazaundecanediamide (4- Me- L- 2, 3, 2) and thw two deprotonation constants of each of these complexes have been determined potentiometrically in 0.10 M Na CLO4 , at 25℃. Electronic spectra of these complexes and their deprotonated species formed in aqueous solution were measured and discussed. The complexation and dissociation kinetics of these nickel(Ⅱ) complexes have been studied by using the stopped-flow technique. The possible pathways for the reactions of nickel(Ⅱ) with these ligands are discussed. It is proposed that these diamino diamides react with the nickel(Ⅱ) ion by the stepwise formation of coordinate bonds, where the rate-determining step is the formation of the first nickel-nitrogen bond and the subsequent bonding is rapid. Similarly, the dissociation mechanism proposed involves the preequilibration of intermediately bonded species, with the second nickel-nitrogen bond breakage as the rate-determingin step. The reqctivity order for the dissociation reaction is Ni(4- Me- L- 2, 3, 2)2+>Ni(4, 7- Me2- L- 2, 2, 2) 2+>Ni(4- Me- L- 2, 2, 2) 2+>Ni(4- Et- L- 2, 2, 2) 2+. The thermodynamic, spectroscopic, and kinetic data are discussed in relation to a combination of steric, inductive, statistical, solvation, and ring-strain effects. |
