Multicopper(II) Pyromellitate Compounds: Self-Assembly Synthesis, Structural Topologies, and Magnetic Features

Self-assembly syntheses based on the reactions, in aqueous solution at room temperature, of copper(II) nitrate, triethanolamine (H3tea), pyromellitic acid (H4pma), and ammonia or its derivatives (methylamine, ethylamine) give rise to the new Cu(II) 2D [Cu2(μ6-pma)(NH3)4]n·2nH2O (1) and 3D [Cu2(μ-H2O)2(μ4-pma)(MeNH2)4]n (2) coordination polymers and the dimer [Cu2(μ2-pma)(H3tea)2(EtNH2)2] (3). A crucial synthetic and structural role is played by ammonia and its derivatives, acting also as pH regulators. 1−3 have been isolated as air-stable crystalline solids and characterized by IR spectroscopy and elemental and single-crystal X-ray diffraction analyses, the latter showing the formation of infinite 2D (1) and 3D (2) metal−organic frameworks or discrete dimeric blocks (3) adopting distinct structural topologies. The structures are further extended through numerous H-bonding interactions to give 3D (1, 2) and 1D (3) hydrogen bonded supramolecular assemblies. Magnetic susceptibility measurements reveal weak antiferromagnetic coupling between the copper(II) ions. Compound 1 follows the Bleaney−Bowers dinuclear model, 2 the antiferromagnetic chain model, and 3 the Curie−Weiss law. The weak magnetic coupling is explained in terms of the poor overlap between the magnetic orbitals centered at the copper(II) ions through the bridging ligands.