Synthesis, structural characterization, and DFT analysis of zinc(ii) Schiff base complexes featuring noncovalent spodium bonds

Abstract

In this study, we report the synthesis and comprehensive characterization of five novel zinc(II) complexes with Schiff base ligands: [Zn(HL¹)₂] (1), [Zn(HL²)₂]·DMSO·2H₂O (2A), [Zn(HL²)₂]·DMF (2B), [Zn₂(HL³)₄] (3), and [Zn₂(HL⁴)₄]·H₂O (4). SC-XRD confirms the structures of the complexes, revealing diverse coordination environments and noncovalent interactions, including spodium bonds. The role of hydroxyalkyl groups in stabilizing these complexes is highlighted, showing their contribution to both hydrogen and spodium bonds. Theoretical studies, including DFT geometry optimizations using periodic boundary conditions, QTAIM, and NCIPlot analyses, elucidate the nature of these weak interactions. Natural bond orbital (NBO) analysis further demonstrates charge transfer from the lone pair of oxygen atoms to the Zn(II) centers, emphasizing the polarization of the zinc orbitals. These findings advance the understanding of spodium bonding in coordination chemistry and its role in stabilizing supramolecular assemblies.