 kinet studi nickel ii complex sulfur-contain amino acid rate express ethylenediaminetetraacet acid edta ligand exchang reaction nickel cystein rate complex + kedta complex edta two-term rate express characterist squar planar complex agre squar planar configur ni cystein report basi spectral studi edta-independ term rate express acid-catalyz term written complex kn 2 5 10 kedta order 10 -10 edta reaction ni cystein methyl ester reaction ni cystein sulfur-contain amino acid ligand thiol ether kinet differ strike ligand exchang reaction edta triethylenetetramin diethylenetriamin nickel-methionin complex order magnitud faster product mix-ligand complex kinet studi amino acid complex sulfhydryl thiol ether sulfur group support studi equilibrium sulfur coordin squar planar complex sulfhydryl group octahedr complex sulfur coordin thiol ether 