Structural analyses and luminescent properties of a series of lead(ii) metal–organic frameworks based on 2-sulfoterephthalate

Abstract

Hydrothermal reaction of lead(II) salt with monosodium 2-sulfoterephthalate (2-NaH₂stp) and three N-donor auxiliary ligands gives rise to a series of 1D–3D Pb(II) coordination polymers:[Pb(2-Hstp)(o-phen)] (1), [Pb(2-Hstp)(2,2′-bipy)(H₂O)]·H₂O (2), [Pb(2-Hstp) (4,4′-bipy)(H₂O)] (3), [Pb(2-Hstp)(H₂O)] (4), [Pb₃(2-Hstp)(2-stp)(OH)(4,4′-bipy)] (5) and [Pb₂(2-stp) (OH)] (6) (o-phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine and 4,4′-bipy = 4,4′-bipyridine). X-ray diffraction structural analyses of these complexes reveal 1, 3, 4 and 6 crystallize in the monoclinic crystal system of the P2₁/c Space group, while 2 and 5 crystallize in the triclinic Pī space group. Complex 1 possesses 1D left- and right-handed helical double-stranded chains sharing a common axis and Pb nodes, and a great deal of H-bonds and π⋯π interactions between o-phen molecules. For 2, the square H-bond clusters link two left- and right-handed helical single-stranded chains to form 1D dual-chain supramolecular structures. Complex 3 features a 1D bimetallic chain structure containing four left-handed helical chains sharing one common axis: one main helix and three auxiliary helixes in ⋯ABC⋯ order twisting up the main helix. Structural analysis shows that complex 4 presents a 3D 5-connected architecture with the topology symbol as (4⁴, 6⁶). In 5, a 2D double-layer structure arises from the μ₃-OH bridged [Pb₃(OH)] triangle clusters with 2-stp³⁻ anions. The 3D framework of 6 is constructed from a unique tetra-nuclear lead(II) [Pb₄(OH)₂] chair-like motif based on two μ₃-OH groups and 2-stp³⁻ anions, resulting in the (4², 6⁶) topology. Solid-state fluorescence properties for these crystalline materials are also presented.