Toxic metal complexes of macrocyclic cyclen molecule - synthesis, structure and complexing properties
Abstract
Toxic metal (Cd2+, Hg2+, Pb2+, and Ag+) complexes with the tetradentate macrocyclic ligand - cyclen (1,4,7,10-tetraazacyclododecane, [12]aneN(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([12]ane-N-4(1,4,7,10))(NO3)(2))] (1), [Hg([12]ane-N-4(1,4,7,10))(NO3-O-2,O')]NO3 (2), [Pb-2([12]ane-N-4(1,4,7,10))(2)][Pb(NO3)(6)] (3) and one polymeric structure {[Ag-2([12]ane-N-3(1,4,7))((2)-[12]aneN(10))](NO3)(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)degrees, (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 Cd2+ and Pb2+ ions were determined by potentiometric methods in aqueous solutions. Additionally, the structures of complexes in solution were observed by H-1 NMR.
Both methods confirm similar cyclen complexing properties toward Zn2+ biometal and Cd2+, Pb2+ toxic metals.