Derivatives of cyclam-1,8-diacetic acid: Synthesis and complexes with divalent transition metal ions
Abstract
1,4,8,11-tetraazacyclotetradecane-1,8-diacetatic acid, H2te2a, and series of its derivative bearing two sub-stituted N-benzyl groups were synthesized and their complexes were studied. Series of Co(II) and Zn(II) complexes was prepared in the solid-state and X-ray diffraction analysis showed that the metal ions are hexacoordinated by four nitrogen atoms of the macrocycle and two oxygen atoms of the carboxylate pendants.
The two oxygen atoms were in cis and trans mutual position in the Co(II) and Zn(II) complexes, respectively. Potentiometric study of Co(II), Zn(II), Cu(II) and Ni(II)-H2te2a systems showed that the complexes are highly thermodynamically stable and the ligand is selective for Cu(II) ions (logK = 27.5) over the other ions (logK = 21-22).
UV-VIS and electrochemical data for the Co(II)-H2te2a system showed that complexation was rather slow (several hours at pH 4.5, 25 °C) and the complex undergoes slow oxidation with air oxygen.