Spin transition in three-dimensional bridged coordination polymers of iron(II)–urea-triazoles

Three-dimensional spin-crossover (SCO) networks of [Fe2(n-Rdubtrz)3](X)4 · nH2O (n-R = (CH2)y, y = 4, 6, 8, 12; du = diurea; btrz = bis-triazole; X = BF 4 - , ClO 4 - , triflate, tosylate) coordination polymers are prepared by reaction of bridging aliphatic bis-urea triazoles (n-Rdubtrz) with the iron-salts (FeX2). Investigations of the properties are supported by studies of one-dimensional compounds of [Fe(Rtrzu)3](X)2 (R = n-propyl, t-butyl; trzu = urea triazole). Characterization of the complexes is carried out with IR-spectroscopy, elemental analysis, TGA and atomic absorption spectroscopy. SCO-behaviour of all complexes is inspected by magnetic susceptibility measurements and 57Fe Mِssbauer. While the SCO in the polymeric networks shows strong dependency on the counter ions, in the complexes no pronounced change is observed for different methylene bridging lengths. For [Fe(Rtrzu)3](X)2 compounds hysteresis effects are ascertained.