Synthesis, Crystal Structure, Magnetic Properties and57Fe Mössbauer Spectroscopy of the New Trinuclear [Fe3(4-(2′-hydroxyethyl)-1,2,4-triazole)6(H2O)6](CF3SO3)6 Spin Crossover Compound

Abstract

[Fe3(hyetrz)6(H2O)6](CF3SO3)6 [hyetrz = 4-(2′-hydroxyethyl)-1,2,4-triazole] represents the first structurally characterized iron(II) spin crossover compound for which the structure has been solved above and below room temperature in both spin states. The compound crystallizes in the trigonal system, space group R3¯, a = 12.763(1) Å, β = 67.144(1)°, V = 1684.3(1) Å3, Z = 6 at 120 K. At 330 K the space group is retained and a = 13.0183(3) Å, β = 67.376(3)°, V = 1805.8(1) Å3. The molecular structure consists of trinuclear FeII entities linked together by an unprecedented three-dimensional network of hydrogen bonds. This compound shows a gradual spin crossover behavior centered around room temperature, which has been followed by temperature-dependent magnetic susceptibility measurements as well as by 57Fe Mössbauer spectroscopy. The nature of the spin crossover behavior is discussed on the basis of the structural features.