Three novel Co(ii)/Ni(ii)-based coordination polymers as efficient heterogeneous catalysts for dye degradation

Abstract

Three novel networks, namely, {[Co(HL)₂]}_n (1), {[Co(L)(H₂O)]·[Co_3/2(L)(OH-Hbdc)(H₂O)₂]·H₂O}_n (2), and [Ni(L)(H₂O)₅]·DMF·4H₂O (3), where H₂L = 4′-pyridin-4-yl-biphenyl-3,5-dicarboxylic acid and OH-H₂bdc = 5-hydroxyisophthalic acid, have been hydrothermally synthesized and characterized. Compound 1 is a two-dimensional (2D) layered structure of Co²⁺ ions coordinated with incompletely deprotonated HL⁻ ligands. Compound 2 is a crystal in the triclinic space group P and shows a very rare 2D + 2D heterogeneous framework built from 3-connected {6³} hcb layers and 4-connected {4⁴·6²} sql layers. Compound 3 is a 0-D molecular complex crystallized in the chiral space group P2₁2₁2₁, which suggests that symmetry breaking can be driven by the solvent-assisted homochiral helix without any chiral building blocks. In addition, their heterogeneous catalytic oxidation activities toward methyl orange (MO), methyl blue (MB), neutral red (NR), methylene blue (MEB), and safranine T (ST) and the mechanisms in the presence of H₂O₂ have been investigated in detail in aqueous solutions. The results show that the photocatalytic efficiency of NR is the highest for compounds 1–3.