The First 1,3,4-Oxadiazole Based Dinuclear Iron(II) Complexes Showing Spin Crossover Behavior with Hysteresis.

Three new dinuclear complexes [FeII2(μ- L)2]X4 ( L is the bis-tridentate ligand 2,5-bis{[(2-pyridylmethyl)amino]methyl}-1,3,4-oxadiazole and X = ClO4-, BF4- and CF3SO3-) have been synthesized and fully characterized by single-crystal X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility measurements. Upon cooling, a trapped [high-spin-low-spin] state of the iron(II) centres is detected. Depending on the counterion, a pronounced thermal hysteresis is found. In one case, it was possible to observe a space group change that accompanies the spin transition. This is the first system showing spin crossover based on an oxadiazole ligand. [ABSTRACT FROM AUTHOR]