Structural dynamics of a phenoxy-bridged heteronuclear Cu(II)/Hg(II)-Salen complex: synthesis, characterization, DFT insights, and Hirshfeld surface analysis

The synthesis and characterization of a novel heteronuclear Salen complex, CuL–HgI₂, are reported. The complex was characterized using a variety of analytical techniques, including FTIR, UV–Vis, and single-crystal X-ray diffraction. The X-ray diffraction analysis revealed a square planar geometry (CuN₂O₂) for the Cu(II) ion, with the deprotonated phenoxide-type ligand L²⁻ forming N₂O₂. In contrast, the Hg(II) ion is surrounded by two iodine atoms and two oxygen atoms, resulting in a tetrahedral geometry. In the complex, intermolecular interactions were facilitated by weak C−H···I hydrogen bonding; while, the overall framework was stabilized through weak C−H···π and π···π stacking interactions. Using the DFT/B3LYP method and the LanL2DZ basis set, MEP, HOMO, and LUMO analyses were conducted to gain insights into specific molecular properties such as electronegativity, chemical reactivity, chemical hardness, and softness. Calculations of the energies of frontier orbitals were carried out to provide a comprehensive understanding of these properties. To explore the contributions of various intermolecular contacts within the complex, Hirshfeld surface analysis was employed. The analysis revealed that the major contributions to the main interactions originated from H···H (48.5%), I···H (22.5%), and C···H (17.8%) contacts.