Abstract
The macrocyclic tetraamine ligand，1.4.8.11-tetraazacyclotetradecane (cyclam)，was obtained by template synthesis；mono-N-substituted tetraazamacrocyclic compound，1-(2-Pyridylmethyl)-1.4.8.11-tetraazacyclotetra- decane，was accomplished by reaction of a fivefold excess of cyclam with 1 equivalent of the alkylating reagent，2-chloromethylpyridine- hydrochloride。A six-coordinated complex was formed by Ni(ClO4)2.6H2O and this ligand。Substitution reactions of [Ni (cyclam-CH2-Py)(H2O)]2+ with some monodentate ligands at different temperatures were studied by spectrophotometric method。Using the Rose Drago equation，we found that the equilibrium constants of these ligands decrease in the order N3- > SCN- > Cl- > Br-，and it was mainly effected by the basicity of these monodentate ligands。The softness and basicity of this Ni(II) complex could be quantitatively correlated by Edwards equation。According to the values of α，β andα/β obtained by Edwards equation，we could know that the character of this Ni(II) complex we used was between hard and soft acid。Furthermore，we used Eyring equation to analyze the character of the transition state。The negative values of ΔS≠ for different monodentate ligands showed an associative mechanism for these substitution reactions。The observed rate constants kobsd of substitution reactions were obtained at different temperatures using stopped-flow method。The formation rate constants kf of these ligands decrease in the order N3- > SCN- > Cl- > Br-，consisting with basicities of the monodentate ligands。Plots of log kf against logKX at different temperatures gave slopes of 0.97 (25℃)、0.96 (30℃)及0.91 (35℃)，showing an associative mechanism for these substitution reactions。The equilibrum constants， KX，obtained by spectrophotometric method under equilibrum conditions were in agreement with kinetically determined values (kf/ksol)。