• electrochemistry;
  • iron;
  • spin crossover;
  • supramolecular chemistry;
  • X-ray diffraction


A new synthesis of (8-quinolyl)-5-methoxysalicylaldimine (Hqsal-5-OMe) is reported and its crystal structure is presented. Two FeIII complexes, [Fe(qsal-5-OMe)2]Clsolvent (solvent=2 MeOH0.5 H2O (1) and MeCNH2O (2)) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal-5-OMe)2] Cl2 MeOH0.5 H2O (1) exhibits rare crystallographically independent high-spin and low-spin FeIII centres at 150 K, whereas [Fe(qsal-5-OMe)2]Cl MeCNH2O (2) is low spin at 100 K. In both structures there are extensive π–π and C[BOND]H⋅⋅⋅π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped-spin crossover with T1/2=245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half-spin crossover also with a hysteresis of 10 K. The two compounds are the first FeIII complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by 57Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to FeII at −0.18 V and irreversible oxidation of the coordinated qsal-5-OMe ligand at +1.10 V.