The cosolvent-dependent assembly of a family of three blue fluorescent lead(ii)-coordination polymers with 5-amino-2,4,6-tribromoisophthalic acid

Abstract

By modulating the synthetic strategy based on changing the cosolvent in the synthesis, the aqueous medium assembly of lead(II) with H₂ATBIP in the presence of different cosolvents, N,N-dimethylacetamide (DMA), methanol (CH₃OH) or N,N-dimethylformamide (DMF), leads to a family of three lead(II) coordination polymers: [Pb(ATBIP)(H₂O)₂]·2H₂O (1), [Pb(ATBIP)(H₂O)(CH₃OH)]·H₂O (2) and [Pb(ATBIP)(H₂O)(DMF)]·H₂O (3) [H₂ATBIP = 5-amino-2,4,6-tribromoisophthalic acid]. Complex 1 exhibits an interesting double chain structure with [Pb₂(OH₂)₂] as the secondary building unit (SBU), which further assembles into a 3D supramolecular framework through the C–Br⋯Br halogen bonds and hydrogen bonds. Furthermore, the discrete water octamer (H₂O)₈ is found. The cosolvents, DMF and CH₃OH, which simultaneously act as the coordinated small molecules, have significant influences on the formation of different crystalline architectures. Complex 2 features a 2D network constructed by the 2₁ helical carboxylate-bridged Pb(II) chains [Pb₂(COO)₂]_n (SBUs) linked by the ligand ATBIP²⁻. The intralayer C–Br⋯Br halogen bond is found and a 3D supramolecular framework is formed by the interlayer hydrogen bonds. Complex 3 crystallizes in the chiral space group P4₁2₁2 and possesses a 2D (4,4)-homochiral layer built from the centrosymmetrical SBU [Pb₂(COO)₂] bridged by the ligand ATBIP²⁻. The interlayer hydrogen bonds further extend the chiral layers in 3 into a 3D supramolecular homochiral framework. The coordination modes of the ligand ATBIP²⁻ are greatly dependent on the cosolvents. Complex 3 loses crystallinity in the air and forms the material [Pb(ATBIP)(DMF)] (3A). Thermal stability and solid state fluorescent properties of 1, 2 and 3A have been studied. The second harmonic generation (SHG) property of 3A is also studied.