Crystalline features of Schiff base and transition metal complexes: an overview

Abstract

Crystalline Schiff bases (SBs) and their metal complexes play important roles in materials science owing to their distinct physical and chemical properties, diverse compositions, and intriguing structures. These materials exhibit highly ordered geometric arrangements, high solubility, thermal stability, mechanical strength, conductivity, and biodegradability. The crystalline nature of compounds, whether ordered or orientationally ordered liquids, arises from the introduction of various functional groups, such as hydroxyl, carboxyl, nitro, methoxy groups, and halogen atoms, which are responsible for forming hydrogen bonds, interionic interactions, molecular bonding, π–π interactions and van der Waals bonding within metal–organic frameworks (MOFs). The degree of crystallinity and structural order of SB and metal complexes are evaluated using various techniques, including polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Studies on crystalline SB and their complexes will explore their properties and potential future developments to advance their diverse applications, including semiconductors, superconductors, sensors and energy storage devices. This review highlights the design and synthesis of organic–inorganic hybrid assemblies aimed at modifying their properties for next-generation technological advancements, while also discussing how these crystalline features influence the stability, processability and electronic properties of materials, particularly in systems exhibiting or closely related to liquid–crystalline (LC) behaviour.