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

Three-dimensional spin-crossover (SCO) networks of [Fe-2(n-Rdubtrz)(3)](X)(4) center dot nH(2)O (n-R = (CH2)(y), y = 4, 6, 8, 12; du = diurea; btrz = bis-triazole; X = BF4-, ClO4-, 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 Fe-57 Mossbauer. 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. (c) 2008 Elsevier B.V. All rights reserved.