Solvothermal self-assembly of a novel metal-organic square grid complex using a biscarbohydrazone ligand building block: Crystal structures, Hirshfeld and void surface analyses, band gap calculations and DFT studies

Abstract

Here we report the solvothermal self-assembly of a novel metal–organic square complex [Zn(HL)]4Cl2·ZnCl4·16H2O (1) using 1,5-bis(2-benzoylpyridine) carbohydrazone (H2L) ligand building block. Single-crystal X-ray diffraction (SCXRD) study confirm the structure of the complex, which is characterized by other physicochemical methods. The crystal study reveals the presence of a tetrahedral ZnCl42- counter anion also. The DFT quantum chemical calculations and analysis of the square grid cation are explored first time and are compared with the crystal structure and DFT calculations of the ligand building block H2L also. The solid-state band gap (Eg) of the ligand and the square grid complex are determined experimentally using the Kubelka-Munk model and are found to be 3.22 and 1.74 eV respectively. Hirshfeld surface (HS) analyses of both the building block and the complex were also explored to quantify the intermolecular interactions in their crystal lattices. The molecular packing of the complex and the ligand were found to be dominated by isotropic H···H contacts. However, strong H···Cl contacts are contributing the most in the crystal structure cohesion of the complex, while the C···H interactions are the dominating anisotropic forces contributing to the overall Hirshfeld surface in the ligand lattice. The theoretical void space calculations of the complex [Zn(HL)]4Cl2·ZnCl4 (1a) were then carried out. The close packing in the crystal lattice possesses small voids and cavities and an isosurface value of 0.0008 au was found suitable for crystal void calculation, in agreement with PLATON calculations. The corresponding pore volume and the surface area per unit cell were found to be 940.58 Å3 and 1656.04 Å2 respectively.