Organic–inorganic hybrid coordination polymers based on the 5-oxyacetate isophthalic acid (H3OABDC) ligand: syntheses, structures, magnetic and luminescent properties

Abstract

Five new complexes, [Ln(OABDC)(H₂O)₅]_n·2nH₂O [Ln = Sm (1), Eu (2), Dy (3)], [Ni₄(OABDC)₂(OH)₂(H₂O)₄]_n·4nH₂O (4), [Cu₂(OABDC)(4,4′-bipy)_0.5(OH)]_n (5) have been synthesized by the hydrothermal reaction of a unique scorpion-shaped carboxylate ligand (5-oxyacetate isophthalic acid = H₃OABDC) with different lanthanide or transition metals in the presence or absence of auxiliary 4,4′-bipyridine ligand. Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and thermogravimetric analysis. Compounds 1–3 are isostructural: the metal ions are bridged through carboxylate oxygen atoms to form 1D zigzag chains, and adjacent chains are further extended to a 3D supramolecular structure via hydrogen bonds. Compound 4 has a two-dimensional (2D) metal–organic framework based on [Ni₄(μ₃-OH)₂]⁶⁺ clusters, which are further connected by intermolecular hydrogen bonds to form a 3D network. In compound 5, multicarboxylate ligands link Cu centers to generate a 2D sheet structure which is further connected by auxiliary 4,4′-bipyridine ligand to form a 3D structure. Free H₃OABDC ligand and complexes 1, 2 exhibit strong fluorescent emissions in the visible region. Magnetic susceptibility measurements indicate that 4 exhibits weak ferromagnetic coupling between adjacent Ni(II) ions, whereas 5 shows antiferromagnetic coupling between Cu(II) ions.