The hydrate of a neutral iron() complex based on the pyruvic acid thiosemicarbazone ligand with abrupt spin-crossover with = 340 K and a wide hysteresis loop of 45 K

The hydrate of a neutral iron( iii ) complex based on the pyruvic acid thiosemicarbazone ligand [Fe III (Hthpy)(thpy)]·H 2 O ( 1 ) was synthesized and characterized using FT-IR spectroscopy, powder and single-crystal X-ray diffraction, dc magnetic measurements, EPR and 57 Fe Mössbauer spectroscopy. The crystal structure of 1 was determined for the first time. Two distinct chelating ligands Hthpy − and thpy 2− coordinate the Fe( iii ) ion to form the FeN 2 O 2 S 2 octahedron which shows a low spin geometry at 150-350 K. The crystal packing contains infinite chains of the Fe( iii ) complexes as well as water molecules located in cavities. Along the chain, π-π interacting pairs of the Fe complexes are linked by H-bonding. According to the dc magnetic measurements, the complete abrupt spin-crossover with half-transition temperature T 1/2 = 340 K and a hysteresis loop of 45 K occurs in the temperature range of 300-363 K. Based on the X-ray structure of 1 , the Bleaney-Bowers equation for the isolated dimer model was used to approximate the temperature dependence of the magnetic susceptibility in the range of 2-50 K. The defined intradimer exchange constant J exp = −0.498(1) K corresponds to a weak antiferromagnetic exchange between the iron( iii ) magnetic centers. DFT calculations of H- and π-π bonded fragments of the crystal structure of 1 in the HS and LS states were carried out. Moreover, BS-DFT calculations confirm the presence of antiferromagnetic exchange J calc = −0.92 K in the π-π bonded pairs of the ferric complexes and show the exchange pathway between Fe( iii ) ions by the calculated spin density distribution. The iron( iii ) SCO complex based on the pyruvic acid thiosemicarbazone ligand [Fe(Hthpy)(thpy)]·H 2 O was synthesized and characterized using powder and single-crystal X-ray diffraction, dc magnetic measurements, FT-IR, EPR and Mössbauer spectroscopy.