Exploring the syntheses, structures, topologies, luminescence sensing and magnetism of Zn(ii) and Mn(ii) coordination polymers based on a semirigid tricarboxylate ligand

Abstract

Solvothermal reactions of Zn(II) or Mn(II) salts and 2-(4-carboxyphenoxy)terephthalic acid (H₃cpota) in the presence of N-heterocyclic group ligands (1,10-phenanthroline (phen) or 1,4-di(1H-imidazol-1-yl)benzene (bib) or 4,4′-bipyridine (4,4′-bpy)) produced four multi-dimensional coordination polymers, namely, [Mn(μ₃-Hcpota)(phen)]_n·nH₂O 1 (1D), [Mn₂(μ₄-Hcpota)(μ₃-Hcpota)(μ₂-bib)₂(H₂O)]_n2 (3D), [Zn(μ₃-Hcpota)(phen)]_n·nH₂O 3 (2D), and [Zn₂(μ₄-cpota)(μ₂-4,4′-bpy)(μ₃-OH)]_n·nH₂O 4 (3D). Complex 1 features a one-dimensional double ladder formed by syn–anti carboxylate-bridged dimeric Mn(II) units with 8- and 26-membered rings in an alternating pattern sharing three atoms and gives a (4²·6) topology. Complex 2 is formed by linear inorganic chains sharing Mn(II) 8-membered rings in double syn–syn carboxylate bridges and H-bond R¹₁(8) alternate modes, which are further connected to each other by two symmetry independent Hcpota²⁻ ligands as well as coordinated bib bridges giving rise to a three-dimensional net with a novel (4·6²)(4·6⁸·8)(4³·6¹¹·8)(4³·6³) topology. Complex 3 exhibits a two-dimensional layered structure containing 36-membered rings based on 8-membered dinuclear Zn(II) units with (3²·4⁴)(3⁴·4⁶·6⁴·7) fes-net topology. The phen and benzoic acid groups are like two kinds of blades in the two sides of the two-dimensional structure of 3. Complex 4 is an interesting three-dimensional (3,8)-connected network including tetranuclear tricyclic [Zn₄(OH)₂(COO)₆] clusters with a new (4·5·6)₂(4²·5⁶·6¹⁶·7²·8²) topology. The semirigid tricarboxylate ligand (H₃cpota) shows three geometric modes in the self-assembly of four coordination polymers: a) ‘L’ shape in 1, b) ‘I’ shape in 2 and 3, and c) ‘T’ shape in 4. Magnetization analyses disclose the antiferromagnetic behaviors of 1 and 2. Complexes 3 and 4 feature good solvent stability and can withstand ten common solvents. Luminescence investigations reveal that complex 3 has a highly sensitive, selective, low detection limit and well-recyclable properties in the detection of hexavalent chromium anions in aqueous solution. Quenching mechanisms are also studied in detail.