Synthesis, crystal structure and antifungal activity of an ethylenediammonium-templated nickel(II) pyromellitate coordination polymer

Coordination polymers represent an important class of inorganic-organic hybrid materials constructed from metal nodes interconnected by multidentate organic ligands. Here, a one-dimensional anionic coordination polymer, namely, catena-poly[ethylenediammonium [tetraaquanickel(II)]-μ-benzene-1,2,4,5-tetracarboxylato] dihydrate], {(C₂H₁₀N₂)[Ni(C₁₀H₂O₈)(H₂O)₄]·2H₂O}n, (1), constructed from NiII ions and pyromellitate (benzene-1,2,4,5-tetracarboxylate, btec⁴⁻) ligands has been successfully synthesized through an amine-templating strategy; notably, the polymeric framework does not form in the absence of the amine template, underscoring the decisive structure-directing role of the amine. The obtained polymeric system was characterized by spectral, elemental, thermal and single-crystal X-ray diffraction techniques. Single-crystal X-ray diffraction shows that the centrosymmetric btec⁴⁻ ligand bridges two NiII centres in a trans-monodentate coordination mode through two deprotonated carboxylate groups, forming an extended one-dimensional anionic chain. The remaining two trans-disposed carboxylate groups of btec⁴⁻ remain uncoordinated. Each NiII centre adopts a distorted octahedral coordination geometry, with two sites occupied by carboxylate O atoms of bridging btec⁴⁻ ligands, coordinated in a monodentate fashion, and the remaining four sites occupied by coordinated water molecules. Protonated ethylenediammonium cations are aligned parallel to the polymeric chains and act as counter-ions to maintain charge balance. Extensive O-H...O and N-H...O hydrogen-bonding interactions link the chains into a multidimensional supramolecular architecture. Compound (1) exhibits appreciable water solubility and solvent processability. Preliminary antifungal studies indicate significant inhibitory activity against Candida albicans.