The role of ligand design affecting the thermal and light-induced spin transition in mononuclear iron(II) complexes

Molecules are increasingly considered for information processing and sensing applications. Therefore, much research has focused on the improvement of such property changes, especially the ability to observe the switching at room temperature. The relationship between chemical structure and spin state in a transition metal complex has an important bearing on the design of spin crossover materials. Thus, ligand design has been the focus of much attention. It has allowed generation of highly cooperative spin-transition iron (II) complexes to promote hysteretic effects. We present herein the thermal and light-induced magnetic properties of several photoswitchable precursors based on a bidentate ligand (phenanthroline), and a monodentate ligand such as a pyridine or picoline derivative. These results were discussed on the basis of the alkyl-substituted pyridine ligand effects on the magnetic and phtomagnetic properties of mononuclear iron (II) complexes. Interestingly, single crystals were obtained for the 4-cyano-pyridine derivate allowing the X-ray diffraction crystal-structure determination.