New mixed-ligand Ni(II) and Zn(II) macrocyclic complexes with bridged (endo,endo)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate: Synthesis, characterization, antimicrobial and cytotoxic activity

Abstract

New carboxylate complexes of the tetraazamacrocyclic ligand N,N',N'',N'''-tetrakis(2-pyridilmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) with Ni(II) and Zn(II) as central ions were prepared. In mixed-ligand com­plexes (endo,endo)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate dianion (C₉H₈O₄^2-) is also coordinated to metal ions. The complexes were characterized by ele­men­tal analysis (C, H, N), FTIR and UV–Vis spectroscopy, molar conductivity determination and magnetic susceptibility measurement at room temperature. The analytical data of the complexes show the formation of binuclear [Ni₂(C₉H₈O₄)tpmc](ClO₄)₂·4H₂O and tetranuclear [Zn₄(C₉H₈O₄)(tpmc)₂](ClO₄)₆· ·CH₃CN·KClO₄·4H₂O complexes. In tetranuclear Zn(II) complex bicyclic dicarboxylate ligand is most likely to be bridge coordinated, and in binuclear Ni(II) complex it is coordinated in a combined bridged manner with chelate rings formation. In both complexes macrocyclic ligand was exo coordinated, out of cyclam ring and adopts a boat conformation. The Zn(II) complex is one of the rare tetranuclear Zn(II)-tpmc complexes with carboxylate ion bridging two Zn₂tpmc units. The complexes were tested for antibacterial activity against Gram-positive bacteria Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6633), Gram-negative bacterium Escherichia coli (ATCC 25922), and yeast Candida albicans (ATCC 10231), and were screened for antiproliferative activity against human cervix adenocarcinoma (HeLa) and human myelogenous leukemia (K562) cell lines.