Synthesis, Structural Characterization, Hirschfeld Surface Analysis, Density Functional Theory, and Photocatalytic CO₂ Reduction Activity of a New Ca(II) Complex with a Bis-Schiff Base Ligand

A new bis-Schiff base (L) Ca(II) complex, CaL, was synthesized by the reaction of calcium perchlorate tetrahydrate, 1,3-diamino-2-hydroxypropane, and 2-formyl phenoxyacetic acid in an ethanol-water (v:v = 2:1) solution and characterized by IR, UV-vis, TG-DTA, and X-ray single crystal diffraction analysis. The structural analysis indicates that the Ca(II) complex crystallizes in the monoclinic system, space group P12(1)/n1, and the Ca(II) ions are six-coordinated with four O atoms (O8, O9, O11, O12, or O1, O2, O4, O6) and two N atoms (N1, N2, or N3, N4) of one bis-Schiff base ligand. The Ca(II) complex forms a tetramer by intermolecular O-H horizontal ellipsis O hydrogen bonds. The tetramer units further form a three-dimensional network structure by pi-pi stacking interactions of benzene rings. The Hirschfeld surface of the Ca(II) complex shows that the H & sdot;& sdot;& sdot;H contacts represent the largest contribution (41.6%) to the Hirschfeld surface, followed by O & sdot;& sdot;& sdot;H/H & sdot;& sdot;& sdot;O and C & sdot;& sdot;& sdot;& sdot;H/H & sdot;& sdot;& sdot;C contacts with contributions of 35.1% and 18.1%, respectively. To understand the electronic structure of the Ca(II) complex, the DFT calculations were carried out. The photocatalytic CO2 reduction test of the Ca(II) complex exhibited a yield of 47.9 mu mol/g (CO) and a CO selectivity of 99.3% after six hours.