Toxic metal (Cd 2+ , Hg 2+ , Pb 2+ , and Ag + ) complexes with the tetradentate macrocyclic ligand - cyclen (1,4,7,10-tetraazacyclododecane, 12aneN 4 , 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(12ane-κ 4 N 1,4,7,10 )(NO 3 ) 2 ) (1), Hg(12ane-κ 4 N 1,4,7,10 )(NO 3 -κ 2 O,O`)NO 3 (2), Pb 2 (12ane-κ 4 N 1,4,7,10 ) 2 Pb(NO 3 ) 6 (3) and one polymeric structure {Ag 2 (12ane-κ 3 N 1,4,7 )(μ 2 -12aneN 10 )(NO 3 ) 2 ∙2H 2 O)} n (4) featuring a unique coordination mode not observed before with cyclen as a ligand. The monodentate (1) and chelate (with small bite angle 50.3(3)°, (2) coordination modes of nitrate ligands were confirmed. Stereochemically active 6s 2 lone pair was suggested in 3 and DFT results confirmed no significant metal-metal covalent bond. The stability constants of the complexes with Cd 2+ and Pb 2+ ions were determined by potentiometric methods in aqueous solutions. Additionally, the structures of complexes in solution were observed by 1 H NMR. Both methods confirm similar cyclen complexing properties toward Zn 2+ biometal and Cd 2+ , Pb 2+ toxic metals.