Cobalt(II) and magnesium(II) complexes with 1,3-pdta-type of ligands: influence of an alkyl substituent at 1,3-propanediamine chain on the structural and antimicrobial properties of the complex

To investigate how modification in the structure of 1,3-propanediamine chain of 1,3-pdta (1,3-propanediamine-<i>N,N,N′,N′</i>-tetraacetate) ligand affects the structural and biological properties of the corresponding metal complexes, two new octahedral complexes, [Co(H₂O)₅Co(2,2-diMe-1,3-pdta)]·H₂O (<b>1</b>) and [Mg(H₂O)₅Mg(2,2-diMe-1,3-pdta)]·1.5H₂O (<b>2</b>) (2,2-diMe-1,3-pdta = 2,2-dimethyl-1,3-propanediamine-<i>N,N,N′,N′</i>-tetraacetate), were synthesized and characterized by IR spectroscopy and single-crystal X-ray diffraction analysis. Additionally, UV-Vis and NMR spectroscopic methods were applied for the characterization of <b>1</b> and <b>2</b>, respectively. Crystallographic data indicate that these complexes contain 2,2-diMe-1,3-pdta coordinated to the metal ion through 2 N and 4 O atoms forming [M(H₂O)₅M′(2,2-diMe-1,3-pdta)] complex unit (M, M′ = Co(II), Co(II) (<b>1</b>) and M, M′ = Mg(II), Mg(II) (<b>2</b>)), which is composed of [M′(2,2-diMe-1,3-pdta)]²⁻ and [M(H₂O)₅O]²⁺ octahedra bridged by one of the axial carboxylate groups. The antimicrobial activities of <b>1</b> and <b>2</b> were evaluated against different bacteria and <i>Candida</i> spp., while their cytotoxic effect was tested on the normal human lung fibroblasts (MRC-5). The ability of <b>1</b> and <b>2</b> to inhibit formation of <i>C. glabrata</i> biofilms was also assessed. The obtained structural parameters and biological properties of the two complexes were compared to Co(II) and Mg(II) complexes with 1,3-pdta ligand.