Structure and spectroscopic properties of a three-dimensional PbII coordination polymer constructed from 1,1′-biphenyl-2,2′,4,4′-tetracarboxylate

The title coordination polymer, poly[aqua(μ ₈ -1,1′-biphenyl-2,2′,4,4′-tetracarboxylate)lead(II)], [Pb ₂ (C ₁₆ H ₆ O ₈ )(H ₂ O) ₂ ] _n , (I), was constructed by a multidentate ligand 1,1′-biphenyl-2,2′,4,4′-tetra- carboxylic acid (abbreviated as H ₄ bpta) under hydrothermal condition. In the structure, two crystallographically independent Pb(II) cations exhibit different coordination geometries, wherein one of the Pb(II) ions is holodirected and coordinated by eight oxygen atoms [PbO ₈ ] and another chelated by carboxylates, is slightly hemidirected and coordinated by seven oxygen atoms [PbO ₇ ] [1]. The bpta ⁴⁻ ligand connects eight Pb(II) atoms by adopting the μ ₈ -bridging mode. The carboxylate groups (2,2′-COO ⁻ ) are in μ ₄ -η ¹ :η ² :η ² :η ² -chelating/bridging, and the other two (4,4′-COO ⁻ ) are in μ ₄ -η ¹ :η ² :η ¹ :η ² fashion. In addition, the structure of (I) consists of 1D chains built by carboxylate groups bridging a pair of quad-core cluster [Pb ₄ O ₄ ] units, which is further linked through bpta ⁴⁻ to generate a unique 3D open framework. The coordination polymer is reinforced by intermolecular hydrogen bonding between oxygen atoms of the carboxylate groups, and coordination water molecules. The complex has also been characterized by PXRD, thermoanalysis, and luminescence.