Synthesis, Crystal structure, Hirshfeld surface, Thermal analysis and DFT Calculations of Zn(II) complex of mixed ligand from 2,4-dichlorophenoxy acid (2, 4-D) and ethylenediamine (en)

Abstract

A novel Zn(II) complex, [Zn(2,4-D)₂(en)], has been synthesized via the reaction of zinc acetate with 2,4-dichlorophenoxy acid (2,4-D) and ethylenediamine (en). The complex was characterized entirely by spectroscopic, elemental analysis, and single X-ray crystallography techniques. According to the crystallographic analysis of the metal complex, it was revealed that the structure exhibited a tetrahedral shape, with coordination with two carboxylate oxygen atoms and two nitrogen atoms; those donating atoms come from the 2,4-D and ethyleniamine groups, respectively. Using Density Functional Theory (DFT) with the B3LYP/def2-TZVP basis set, the analysis of the complex provided insights into its electronic structure. The frontier molecular orbitals, with a HOMO at -5.90 eV and a LUMO at -0.53 eV, showed a HOMO-LUMO gap of 5.37 eV, reflecting potential stability and reactivity. Electrostatic potential (ESP) analysis also revealed significant charge distributions, particularly at oxygen atoms, highlighting their importance in stability and intermolecular interactions. Hirshfeld surface analysis elucidated significant intermolecular contacts in the packing, with H•••Cl/Cl•••H interactions being the most prevalent (30.6%), followed by H•••O/O•••H interactions (23.9%). Moreover, thermal decomposition studies illustrated a ca. 60% mass reduction observed in the temperature range of 236-384°C.