A Hobson's Choice Co‐Ligand in Imparting Spin Crossover in Fe(II) Complexes Based on 1,3,4‐Oxadiazole Ligands

Abstract In this manuscript we report the synthesis of three methanol solvatomorphs of Fe(II) complexes with the 2‐(2‐phenyl)‐5‐[N,N‐bis(2‐pyridylmethyl)aminomethyl]‐1,3,4‐oxadiazole ( L Ph−ODA ) ligand and three different NCE co‐ligands where E=S, Se and BH 3 ( C1 – C3 ). The complexes obtained were characterized by single crystal X‐ray crystallography and SQUID magnetometry between 2 and 300 K. Complexes C1 and C2 remain in the high spin state over the entire measured temperature window, whereas complex C3 exhibits a solvent dependent spin transition with a T 1/2 of 166 K. Upon heating the sample to 400 K and removing methanol, the complex exhibited a two‐step spin transition with the first step having a T 1/2 of 215 K and a second step having a T 1/2 of 137 K.