Structural characterization and antimicrobial evaluation of chromium(III) and cobalt(III) complexes with 2,2-diMe-1,3-pdta: Tuning dimensionality of coordination polymer and the water content by alkyl substitution

Abstract

Hexadentate 2,2-dimethyl-1,3-propanediamine-N,N,N’,N’-tetraacetate (2,2-diMe-1,3-pdta) ligand, containing two methyl substituents at the central carbon atom of a 1,3-propanediamine, has been prepared and used for the synthesis of Na[Cr(2,2-diMe-1,3-pdta)]·3.75H2O (1) and Na[Co(2,2-diMe-1,3-pdta)]·3.88H2O (2) complexes. These complexes were characterized by IR and electronic absorption spectroscopy, and single-crystal X-ray diffraction analysis. NMR (1H and 13C) spectroscopy was additionally applied for the characterization of complex 2. Crystallographic data indicate that the two investigated crystals are isostructural and contain 2,2-diMe-1,3-pdta ligand coordinated to metal ion through 2N and 4O atoms forming an octahedral complex in which the six-membered 1,3-propanediamine chelate ring adopts a twist-boat conformation. There are four such complex anions in the symmetry independent part of the unit cell. Each complex anion is further connected to the sodium counterion(s) via the bridging carboxylate group(s). Structural changes in 2,2-diMe-1,3-pdta-Cr(III) complex stimulated solely by the presence of alkyl side groups are discussed. The present study shows that in 1,3-pdta-type complexes of Cr(III) and Co(III), the environment at coordination centre can be modified by introducing substitution in one of the carbon atoms of the diamine and the resulting difference in the subunit structure can bring about noticeable change in molecular and crystal structure. The examples illustrate the importance of the steric effect for the fine tuning of the dimensionality of the resulting coordination polymer and the water content. The antimicrobial activity of complexes 1 and 2 was evaluated against different bacterial and Candida spp., while their cytotoxic effects were tested on the normal human lung fibroblast cell line (MRC-5).