Synthesis, Structural Characterization and Hirshfeld Surface Analysis of a Novel Cd(II) Coordination Polymer with Mixed N- and O-donor Linker

Abstract

In the present study, we report the room temperature synthesis of a novel two-dimensional (2D) coordination polymer (CP) having the formula {[Cd(H-PCA)₂(H₂O)]·0.5(H₂O)·0.5(CH₃OH)}_n (CP1), where H-PCA represents 4-pyrazolecarboxylate. The synthesis of CP1 was achieved through a one-pot reaction, involving the self-assembly of Cd(OAc)₂·2H₂O and the multitopic mixed N- and O-donor ligand, 4-pyrazolecarboxylic acid (H₂-PCA), in methanol. This method demonstrated high yield and purity, enabling the facile production of multigram quantities of CP1 within a short timeframe. Notably, the synthetic procedure selectively deprotonates the carboxylic acid group while retaining the pyrazole moiety in its protonated form. CP1 has been thoroughly characterized using various analytical techniques, including single-crystal X-ray diffraction, FTIR spectroscopy, elemental analysis, scanning electron microscopy, thermogravimetric analysis, and powder X-ray diffraction. The structural analysis revealed that CP1 features a 3, 5-connected binodal net with the point symbol {4.5.6}{4.5⁵.6³.7}, leading to a unique -ths net topology. Through hydrogen bonding connections between adjacent 2D sheets, CP1 further extends into a three-dimensional (3D) supramolecular network due to the presence of coordinated water molecules and the protonated pyrazole group. Additionally, a 3D Hirshfeld Surface analysis accompanied by quantitative 2D fingerprint plots was also investigated to explore the intermolecular interactions.