Spin crossover tuning through ligand design: Magnetic measurements, Mõssbauer and crystal structures of two isomeric Fe(ll) complexes with 2-aryl-imidazole ligands

Designing coordination complexes that are stable and exhibit spin crossover (SCO) phenomenon are highly in vogue because of their applications in memory storage and switching devices. lmidazole has a bifunctional character i.e., the presence of pyrrolic and pyridinic N-atom, in addition to its -NH functional group which makes it a perfect candidate for manipulation of the ligand field strength, to trigger interesting electrochemical and magnetic properties in the corresponding metal complexes. ln the present work, Mõssbauer Spectroscopy and magnetic susceptibility measurements were used to study the spin crossover phenomena in two complexes [Fe(M)3](CIQ4)2 (1) and [Fe(Z)3](CIQ4)2 (2). Single crystals of both the complexes showed distorted octahedral form of the meridional isomers with a space group P 21 / c at 150 K. Mõssbauer Spectroscopy (Figure 1) for complex (1) proves the existence of both HS and low spin configurations at ambient temperature whereas only LS state ata lower temperature (22K). However, complex (2) was found to exist in low spin only ata wide range from ambient temperature to 22K. Magnetic susceptibility experiments also endorsed the aforementioned results. Complex (1) was found to be a spin crossover compound with a spin transition at 225 K, whereas complex (2) had a stable magnetic behavior between 0- 300 K. Therefore, ligand design can be considered as a potential tool to manipulate and fine tune the magnetic properties of these complexes.