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O zjawisku spin-crossover. Polimeryczne kompleksy Fe(II) z pochodnymi 1,2,4-triazolu

Połomka P.

Wiadomości Chemiczne

2004

[Z] 58, 5-6

477--496

This paper is a short review of a spin-crossover phenomenon in complexes of iron(II). This phenomenon is related to the thermally induced transition between a diamagnetic low spin ground state (LS or S=0) and the excited paramagnetic high spin state (HS or S=2). Numerous compounds switch from a stable electronic state to another state in a reversible and detectable fashion in response to an appropriate and controllable external perturbation. This transition is accompanied by a strong thermochromism between rose and white colors. In certain cases, a hysteresis effect is accompanying this transition, which confers a memory effect to the system. The potential applications of spin transition (ST) molecular materials in the field of display and data processing has led to intensive studies of this phenomenon in the last ten years. For this purpose the compounds need to show a large thermal hysteresis, with the middle of the hysteresis loop falling as close as possible to room temperature. To achieve this goal iron(II) ST molecular materials are designed and synthesized as polymers in order to increase intermolecular interactions. In this paper some polymers based on 1,2,4-triazole derivatives are described because of their bridging nature leading to a strong cooperativity. The influence of various parameters, namely type of counter ion, R substituent in 4- position in the triazole ring, number of noncoordinated lattice water molecules, on the structure and ST regime of Fe(II)-1,2,4-triazole polymers is depicted. Some of the compounds presented might be of potential use as the electronic displays or switches.