Design and characterization of Fe(II) complexes with tetradentate ligands exhibiting spin-crossover near room temperature

Construction of spin-crossover (SCO) materials is very appealing for applications such as molecular switches and information storage. This study focuses on the design of Fe(II) complexes using N,N′-bis(2-pyridinylmethyl)-1,2-ethanediamine-based ligands with an N4 structure for SCO material development. By incorporating para-substituted benzene groups into the ligand's pyridine moiety, two polymorphs, α and β, were obtained, both exhibiting SCO activity. Notably, the β polymorph displayed a spin crossover temperature of 270 K, which is approaching room temperature. Structural analyses were conducted to compare the differences between the polymorphs, along with a literature review of related complexes, providing insights into the characteristics of SCO behavior.