Supramolecular networks assembled from binuclear complexes with pyridazine-3,6-dicarboxylate

Abstract

Solvothermal reactions of dimethyl pyridazine-3,6-dicarboxylate and appropriate metal chlorides in the absence/presence of KCl, NaCl or NH4Cl yielded a series of coordination compounds of pyridazine-3,6-dicarboxylate (pzdc) with Mn(II), Co(II), Ni(II) and Zn(II). All the Mn(II) compounds contain the anionic binuclear motif [Mn2(pzdc)3]2− with the trigonal prismatic shape. Through the K/Na-O electrostatic coordination, charge-assisted N–H⋯O hydrogen bonds, and weak C–H⋯O hydrogen-bonds, the binuclear prismatic anion co-assembles with different cations ([Mn(H2O)6]2+, K+, Na+ or NH4+) to generate 3D architectures. Under similar synthetic conditions, the Co(II) and Ni(II) ions always give the neutral binuclear molecules [M2(pzdc)2(H2O)4], which are self-assembled into 3D hydrogen-bonded networks. The Zn(II) ion seems to be amphibious: in the presence of NH4+, K+ and Na+, it forms the [Zn2(pzdc)3]2− species that are isostructural with the Mn(II) species, but the absence of the above cations leads to [Zn2(pzdc)2(H2O)4], which is isomorphous with the Co(II) and Ni(II) compounds. The different structures have been qualitatively explained based on the metal ionic size, ligand constraints, inter-ligand repulsion, ligand-field effects, and anionic–cationic interactions. Magnetic studies on selected Mn(II) compounds reveal that weak antiferromagnetic coupling is operative through the triple pyridazine bridges within the prismatic anions.