The spin-crossover (SCO) phenomenon is one of the most prominent examples of bi-stability in molecular chemistry, and the SCO complexes are proposed for nanotechnological applications such as memory units, sensors, and displays. Since the discovery of the SCO phenomenon in tris(N,N-dialkyldithiocarbamato)iron(III) complexes, numerous investigations have been made to obtain bi-stable SCO complexes undergoing spin-state switching at or around room temperature (RT). Valiant efforts have also been made to elucidate the structure–property relationship in SCO complexes to understand the factors—such as ligand-field strength, molecular geometry, and intermolecular interactions—governing the SCO. Schiff base ligands are an important class of nitrogen-rich chelating ligands used to prepare SCO complexes, because the Schiff base ligands are easy to synthesize and tailor with additional functionalities. Iron(II)-Schiff base SCO complexes are a well-studied class of SCO active complexes due to the propensity of the complexes to undergo bi-stable SCO. In this context, this perspective attempts to elucidate the structure–SCO property relationships governing SCO in selected mono-, bi-, and multi-nuclear iron(II)-Schiff base complexes.

The breakthrough in Ln(III)-based SMMs with Schiff base ligands have been occurred for the last decade on account of their magnetic behavior, anisotropy and relaxation pathways. Herein, we review the synthetic strategy, from a structural point of view and magnetic properties of mono, di, tri and polynuclear Ln(III)-based single-molecule magnets mainly with Schiff bases of Salicylaldehyde origin. Special attention has been given to some important breakthroughs that are changing the perspective of this field with a special emphasis on slow magnetic relaxation. An overview of 50 Ln(III)-Schiff base complexes with SMM behavior, covering the period 2008–2020, which have been critical in understanding the magnetic interactions between the Ln(III)-centers, are presented and discussed in detail.

Magnetically recyclable C-doped TiO₂/Fe₃O₄ (C-TiO₂/Fe₃O₄) nanocomposite was successfully synthesized via a sol–gel method. The synthesized samples were characterized using SEM, energy-dispersive X-ray spectroscopy (EDS), FTIR, and UV-VIS diffuse reflectance spectroscopy (DRS) techniques. The results clearly showed that a C-TiO₂/Fe₃O₄ nanocomposite was produced. The photocatalytic activities of the prepared pristine (TiO₂), C-doped TiO₂ (C-TiO₂) and C-TiO₂/Fe₃O₄ were evaluated by the photodegradation of methyl orange (MO) under natural sunlight. The effect of catalyst loading and MO concentration were studied and optimized. The C-TiO₂/Fe₃O₄ nanocomposite exhibited an excellent photocatalytic activity (99.68%) that was higher than the TiO₂ (55.41%) and C-TiO₂ (70%) photocatalysts within 150 min. The magnetic nanocomposite could be easily recovered from the treated solution by applying external magnetic field. The C-TiO₂/Fe₃O₄ composite showed excellent photocatalytic performance for four consecutive photocatalytic reactions. Thus, this work could provide a simple method for the mass production of highly photoactive and stable C-TiO₂/Fe₃O₄ photocatalyst for environmental remediation.

Supramolecular architectures, which are formed through the combination of inorganic metal cations and organic ligands by self-assembly, are one of the techniques in modern chemical science. This kind of multi-nuclear system in various dimensionalities can be implemented in various applications such as sensing, storage/cargo, display and molecular switching. Iron(II) mediated spin-crossover (SCO) supramolecular architectures with Schiff bases have attracted the attention of many investigators due to their structural novelty as well as their potential application possibilities. In this paper, we review a number of supramolecular SCO architectures of iron(II) with Schiff base ligands exhibiting varying geometrical possibilities. The structural and SCO behavior of these complexes are also discussed in detail.

A mononuclear Co(II) complex of a Schiff base ligand derived from 5-Bromo-vanillin and 4-aminoantipyrine, that has a compressed tetragonal bipyramidal geometry and exhibiting field-induced slow magnetic relaxation, has been synthesized and characterized by single crystal X-ray diffraction, elemental analysis and molecular spectroscopy. In the crystal packing, a hydrogen-bonded dimer structural topology has been observed with two distinct metal centers having slightly different bond parameters. The complex has been further investigated for its magnetic nature on a SQUID magnetometer. The DC magnetic data confirm that the complex behaves as a typical S = 3/2 spin system with a sizable axial zero-field splitting parameter D/hc = 38 cm⁻¹. The AC susceptibility data reveal that the relaxation time for the single-mode relaxation process is τ = 0.16(1) ms at T = 2.0 K and B_DC = 0.12 T.