Synthesis, structure and coordination properties of three cyclam-based ligands bearing one scorpionate arm

In this work, three new cyclam-based ligands L1, L2 and L3 bearing N-sulfonylacetamide pendant arm and their Cu(II), Zn(II), Cd(II) and Pb(II) complexes were synthesized and characterized by mass spectrometry, NMR, infrared and UV–Vis spectroscopies. The ligands present an original zwitterionic form in which the nitrogen atom of the sulfonylacetamide is deprotonated and one nitrogen of the macrocycle is protonated. This observation was confirmed by X-ray crystallography. The infrared spectra of the ligands revealed very low CO vibrational band values which can be explained by the fact that the oxygen atom is involved in some hydrogen bonds. The amidate form of the sulfonylacetamide arm is maintained upon complexation. Infrared data revealed a probable different coordination mode for Pb(II) than for the other three cations. Some additional studies by UV–Vis and EPR spectroscopies were performed for the Cu(II) complexes. Finally, the geometry coordination of the Cu(II) L3, Zn(II) L3 and Cd(II) L3 complexes in the solid state was studied by X-ray crystallography.