A novel Ca(II) coordination polymer with 3-(3-carboxyphenyl)-isonicotinic acid: design, DFT analysis, and catalytic efficiency

The traditional strategies to improve the catalytic performance of metal complexes mainly focus on the selection of ligands and central metal ions. Herein, a novel calcium(II) coordination polymer, abbreviated as [Ca(L)(H₂O)₃]_n·H₂O, was synthesized by assembling 3-(3-carboxyphenyl)-isonicotinic acid (H₂L), NaOH, and calcium perchlorate tetrahydrate. Its structure was thoroughly investigated using elemental analysis, infrared spectroscopy, UV/vis spectroscopy, and thermogravimetric analysis. The structure of the calcium(II) coordination polymer was further ascertained by single-crystal X-ray diffraction, revealing that each Ca(II) ion is eight-coordinated with five oxygen atoms from three different L ligands and three oxygen atoms from three coordinated water molecules, forming a distorted square antiprism geometry. To gain further insight into the structure, DFT studies were also conducted. The frontier molecular orbitals of the Ca(II) coordination polymer show that the DFT energy gap is 0.12279 Ha (3.34 eV). The electrostatic potential results reveal that regions with higher electrostatic potential are primarily concentrated in the six-member carbon ring structures of the Ca(II) coordination polymer. Conversely, areas with lower potential are mainly located near oxygen and nitrogen atoms. Additionally, the catalytic efficiency of the studied polymer showed that it can achieve a 68.7% conversion of benzyl alcohol and a 40.1% yield of benzaldehyde under 5 bar of O₂ for 2 h in THF.