Synthesis, structure and properties of Nickel(II) and Cobalt(II) compounds with 1,5-dinitronaphthalene-3,7-dicarboxylate

Two metal–organic compounds, [Co2(NNDC)2(H2O)6]·2H2O (1) and [Ni(NNDC)(H2O)4]n (2) (where H2NNDC = 1,5-dinitronaphthalene-3,7-dicarboxylic acid) have been synthesized under hydrothermal reaction conditions, which are characterized by single crystal X-ray determination, IR and Thermogravimetric Analysis (TGA). Compound 1 consists of binuclear Co(II) molecules with di(μ-aqua)di(μ-carboxylato) bridges. In the compound, each dicarboxylate ligand bridges metal ions using only one carboxylate group, with the other carboxylate group involved in extensive hydrogen bonding with coordinated and uncoordinated water molecules. The 1,5-dinitronaphthalene groups serve as pillars between the hydrogen-bonded layers in which the dinuclear moieties are connected through the O–H⋯O⋯H–O hydrogen bonds mediated by uncoordinated carboxylate groups and lattice water molecules. In 2, the ligands serve as long bridges to link the metal ions into infinite chains. The uncoordinated oxygen atoms of carboxylate are hydrogen bonded to coordinated water molecules from the same and different chains to link the metal spheres into (4,4) layers, which are formally pillared by the 1,5-dinitronaphthalene spacers to generate a 3D architecture with the α-Po topology. Based on a model taking into account both magnetic coupling and single-ion magnetic effects, detailed magnetic analysis on the Co(II) compound revealed a ferromagnetic intradimer interaction through the mixed aqua and carboxylate bridges.