Spin Crossover in Bipyridine Derivative Bridged One-Dimensional Iron(III) Coordination Polymer

Herein, the syntheses, solid-state molecular structures, and characterization of two types of one-dimensional Fe-III coordination polymers showing thermally induced spin crossover are reported. The reaction of [Fe(acen)Cl] (acen(2-) = N,N'-ethylenebis(acetylacetonylideneaminate) with 3,3'-bpy or 4,4'-bpy (bpy = bipyridine) produced zigzag and linear one-dimensional chain complexes, [Fe(acen)(3,3'-bpy)][BPh4] (1) or [NEt3I-1][Fe(acen)(4,4'-bpy)][BPh4](2)center dot 0.5(4,4'-bpy) (2), respectively, as confirmed by single crystal X-ray diffraction analysis. Variable-temperature single crystal X-ray diffraction measurements, continuous-wave X-band electron paramagnetic resonance (EPR) spectra, Fe-57 Mossssauer spectra, and DC magnetic susceptibility data revealed that complex 1 exhibited a gradual and complete spin crossover at a transition temperature of 212 K, while complex 2 undergoes an incomplete spin crossover even at 400 K.