Synthesis and oxidation kinetics of transition metal complexes

The nickel (II) complexes of the deprotonated pendant-arm macrocycles 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-l,8-diacetic acid (L₁) and 5,12 dimethyl - 7, 14-diphenyl-1,4,8,11 tetraazacycIotetradecane-1,8-diacetic acid (L₂) have been prepared. The oxidation kinetics of these complexes with peroxodisulfate have been studied. Enthalpies and entropies of activation for Ni(II)L₁ are 39.5 ± 5.3 kJ.mol⁻¹ and -115 ± 5 J.K⁻¹. Mol⁻¹; and for Ni(II)L₂ the corresponding values are 42.8 ± 5.1 kJ.mol⁻¹ and -115 ± 5 J.K⁻¹. Mol⁻¹. Outer-sphere oxidation of Ni(II)L, by bis - (triazacyclononane)nickel (III), [Ni(III)(tacn)₂]³⁻, has been studied and a self-exchange rate constant for the [Ni(II)L₁]⁰v- system has been estimated at 55 mol⁻¹ dm³ s⁻¹. -- The rac-Ni(II)L₂ complex and meso-Co(III)L₁₋ have been structurally characterized by X-ray crystallography. The rac-Ni(II)L₂ complex shows a distorted cis-geometry about the metal while the meso-Co(III)L₁₋ complex show a trans octahedral geometry