Synthesis, structure and photocatalytic properties of coordination polymers based on pyrazole carboxylic acid ligands

Abstract

Three new compounds, namely, [Mn(hpcH)(H₂O)₂]·H₂O (1), [Cd(hpcH)(DMF)(H₂O)] (2), [Cu(hpcH₂)₂(H₂O)₂] (3), (hpcH₃ = 5-hydroxy-1H-pyrazole-3-carboxylic acid) were solvothermally synthesized and characterized in detail. Compounds 1 and 2 are coordination polymers (CPs), exhibit two-dimensional (2D) layered structures and crystallize in monoclinic lattices with the C₂/c and P2₁/c space groups, respectively. Compound 3 shows a 3D supramolecular structure constructed from six-coordinated mononuclear Cu²⁺ through hydrogen bonds and π–π stacking interactions. The hpcH₃ ligand behaved in different coordinated modes in the three compounds. It lost two protons in compounds 1 and 2 and one proton in compounds 3. Furthermore, the photocatalytic degradation properties of compounds 1 and 2 were investigated. The results indicate that 1 and 2 show excellent photocatalytic activities for methylene blue (MB) under visible light. The photocatalytic degradation efficiency of 2 reached 96.7% in 90 minutes. The possible photocatalytic mechanisms displayed by CPs 1–2 for the photodegradation of MB have been addressed through the trapping experiment and theoretical calculations.