The Synthesis, Magnetic, and Spectroscopic Properties of Binuclear Iron(III) Complexes Bridged by Pyrazine, 1,1′-Tetramethylenebis(imidazol), or Bis(pyridine) Compounds Exhibiting a Spin-Equilibrium Behavior

Five binuclear iron(III) complexes bridged by pyrazine, 1,1′-tetramethylenebis(imidazol), or bis(pyridine) compounds with the formula of [LFe(Bge)FeL](BPh4)2 have been prepared, and their spin-equilibrium behavior between high-spin(S=5/2) and low-spin(S=1/2) states has been investigated by means of the temperature dependences of the magnetic susceptibilities and the electronic spectra, where Bge denotes pyrazine, 1,1′-tetramethylenebis(imidazol), 4,4′-bipyridine, 4,4′-ethylenebis(pyridine), or 4,4′-vinylenebis(pyridine), L=bis(3-salicylideneaminopropyl)amine, and BPh4−=tetraphenylborate. The pyrazine complex is low-spin, while the bis(imidazole) and the bis(pyridine) complexes snowed a spin-equilibrium between high-spin and low-spin states, accompanied by a striking thermochromism in both the solids and solutions.