Electrical Properties of Cu-Based Coordination Complexes: Insights from In Situ Impedance Spectroscopy

This study examines the influence of ligand design on the structural, optical, and electrical properties of copper-based coordination complexes. Ligands H₂L¹ and H₂L² were synthesized via the reaction of 5-nitrosalicylaldehyde with 2-hydroxy- or 4-hydroxybenzhydrazide. H₄L³ was obtained from the reaction of carbohydrazide and salicylaldehyde, while H₄L⁴ was prepared by condensing 4-methoxysalicylaldehyde with thiocarbohydrazide. The research focuses on two key design elements: (1) the effect of hydroxyl group positioning on the aroyl ring in hydrazide ligands (H₂L¹ vs. H₂L²) and (2) the impact of carbonyl versus thiocarbonyl groups and aldehyde substituents in hydrazone ligands (H₄L³ vs. H₄L⁴). The resulting complexes, [Cu₂(L¹)₂], [Cu₂(L²)₂(MeOH)₃], [Cu₂(L³)(H₂O)₂], and [Cu₂(L⁴)(H₂O)₂], were synthesized and characterized using attenuated total reflectance infrared (IR-ATR) spectroscopy, thermogravimetric analysis (TG), and UV-Vis diffuse reflectance spectroscopy. Their electrical properties were investigated using solid-state impedance spectroscopy (IS). The crystal and molecular structure of the complex [Cu₂(L²)₂(MeOH)₃]∙MeOH was determined by single-crystal X-ray diffraction (SCXRD). This study underscores the pivotal role of ligand modifications in modulating the functional properties of coordination complexes, offering valuable insights for the advancement of materials chemistry.