Toxic metal complexes of macrocyclic cyclen molecule – synthesis, structure and complexing properties

<p>Toxic metal (Cd<sup>2+</sup>, Hg<sup>2+</sup>, Pb<sup>2+</sup>, and Ag<sup>+</sup>) complexes with the tetradentate macrocyclic ligand - cyclen (1,4,7,10-tetraazacyclododecane, [12]aneN<sub>4</sub>, L) were prepared and studied in the solid state by IR, X-ray diffraction, elemental and thermal analysis. Diffraction results have yielded three molecular structures, [Cd([12]ane-<i>κ</i><sup>4</sup>N<sup>1,4,7,10</sup>)(NO<sub>3</sub>)<sub>2</sub>)] (<b>1</b>), [Hg([12]ane-<i>κ</i><sup>4</sup>N<sup>1,4,7,10</sup>)(NO<sub>3</sub>-<i>κ</i><sup>2</sup>O,O`)]NO<sub>3</sub> (<b>2</b>), [Pb<sub>2</sub>([12]ane-<i>κ</i><sup>4</sup>N<sup>1,4,7,10</sup>)<sub>2</sub>][Pb(NO<sub>3</sub>)<sub>6</sub>] (<b>3</b>) and one polymeric structure {[Ag<sub>2</sub>([12]ane-<i>κ</i><sup>3</sup>N<sup>1,4,7</sup>)(<i>μ</i><sub>2</sub>-[12]aneN<sup>10</sup>)](NO<sub>3</sub>)<sub>2</sub>∙2H<sub>2</sub>O)}<sub>n</sub> (<b>4</b>) featuring a unique coordination mode not observed before with cyclen as a ligand. The monodentate (<b>1</b>) and chelate (with small bite angle 50.3(3)°, (<b>2</b>) coordination modes of nitrate ligands were confirmed. Stereochemically active 6s<sup>2</sup> lone pair was suggested in <b>3</b> and DFT results confirmed no significant metal–metal covalent bond. The stability constants of the complexes with Cd<sup>2+</sup> and Pb<sup>2+</sup> ions were determined by potentiometric methods in aqueous solutions. Additionally, the structures of complexes in solution were observed by <sup>1</sup>H NMR. Both methods confirm similar cyclen complexing properties toward Zn<sup>2+</sup> biometal and Cd<sup>2+</sup>, Pb<sup>2+</sup> toxic metals.</p>