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-polyethylenediammonium [tetraaquanickel (II) -μ-benzene-1, 2, 4, 5-tetracarboxylato] dihydrate], (C2H10N2) Ni (C10H2O8) (H2O) 4·2H2On, (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.