Two Different Coordination Dimers of Pyromellitic Acid in Terms of Molecular Geometry and Supramolecular Architecture

Abstract

Two mixed-ligand coordination dimers, [Ni<inf>2</inf>(pm) (ina)<inf>2</inf>(H<inf>2</inf>O)<inf>4</inf>] (1) and [Mn<inf>2</inf>(Hpm)<inf>2</inf>(ina)<inf>2</inf>(H<inf>2</inf>O)<inf>2</inf>]·H<inf>2</inf>O (2) (pm = tetraanion of pyromellitic acid, Hpm = trianion of pyromellitic acid and ina = isonicotinamide), were comparatively investigated by focusing on their supramolecular architectures. Their structural properties were characterized by X-ray diffraction technique (XRD) and Fourier transform infrared spectroscopy (FT-IR). In 1, each pm4- anion adopts μ<inf>2</inf>-bridging mode to connect two Ni(II) ions through carboxylate groups while in 2 Hpm3- anion bridges Mn(II) ions with tridentate coordination mode of carboxylate groups in cis positions. In 1, 1D H-bonded linear chain consists of R22(8) synthons. Linear chains are inter-connected by O-HO bonds with DA:AD type organization of aqua ligands, resulting in R42(8) synthons to form 2D structure. The increase in the dimensionality of the network is achieved by the involvement of aqua ligands in H-bonds with DD:AA fashion. In 2, the amide group of ina ligand and the aqua ligand involve in DD:AA type H-bond with COO- group of Hpm3- in the formation of ribbon structure. The ribbon structures are inter-connected by H-bonds between the aqua ligands and carboxylate groups, forming 2D supramolecular sheet through R12(4) synthons. Unlike the case of 1, the pyridinium plays an important role to form 3D network of 2 by connecting 2D sheets through R22(22) and R44(30) synthons. The FT-IR investigation of the complexes was performed within the mid-IR region, mainly focusing on the characteristic vibrations of pyromellitic acid and isonicotinamide moieties by considering their free states and ligand behavior in the case of complex formation. © 2015 Elsevier B.V. All rights reserved.