Spin-Transition Polymers: From Molecular Materials Toward Memory Devices

Abstract

Some 3d n (4 ≤ n ≤ 7) transition metal compounds exhibit a cooperative transition between a low-spin (LS) and a high-spin (HS) state. This transition is abrupt and occurs with a thermal hysteresis, which confers a memory effect on the system. The intersite interactions and thus the cooperativity are magnified in polymeric compounds such as [Fe(Rtrz) 3 ]A 2 ·nH 2 O in which the Fe 2+ ions are triply bridged by 4-R-substituted-1,2,4-triazole molecules. Moreover, in these compounds, the spin transition is accompanied by a well-pronounced change of color between violet in the LS state and white in the HS state. The transition temperatures of these materials can be fine tuned, using an approach based on the concept of a molecular alloy. In particular, it is possible to design a compound for which room temperature falls in the middle of the thermal hysteresis loop. These materials have many potential applications, for example, as temperature sensors, as active elements of various types of displays, and in information storage and retrieval.

Spin Switching in Electronic Devices Based on 2D Assemblies of Spin‐Crossover Nanoparticles

“…Such a cooperativity can result in a thermal hysteresis cycle, a property that can be used for memory applications in electronic devices. [5,13] In recent years the size of the SCO solid has been reduced to the nanoscale, while preserving the memory effect near room temperature. In particular, nanoparticles (NPs) of ~10 nm [14,15] have been obtained, based on the polymeric one-dimensional (1D) compound ([Fe(Htrz) 2 (trz)](BF 4 )), (Htrz = 1,2,4-triazole), [16,17] which is one of the most promising SCO systems for designing electronic devices working at room temperature.…”

“…[1][2][3][4] It has been a long standing dream to use this phenomenon in solid-state electronic devices. [5] Only recently several research groups succeeded in electrically addressing SCO materials based on Fe (II) coordination compounds at the nanoscopic [6][7][8] and microscopic [8][9][10] levels. This electric control of the spin has even been achieved in individual SCO molecules.…”

Iron(II) complexes of 2,6-di(1-alkylpyrazol-3-yl)pyridine derivatives – The influence of distal substituents on the spin state of the iron centre

“…The chemistry of spin-crossover complexes [1][2][3] continues to be heavily studied, because of their potential applications as switchable components in memory and display devices [4], in nanoscience [2] and in MRI contrast agents [5]. A class of compound that has been heavily used in spin-crossover research during the past ten years are iron(II) complexes of the isomeric 2,6-di(pyrazolyl)pyridine ligands, 1-bpp and 3-bpp [6, 7].…”

The foundation of modern spin-crossover

“…4), 22 and then used it in a prototype display device. 23 Twenty years later only one more compound is known with similarly favourable spin-switching properties, namely the 5 coordination network [Fe(-pyrazine)Pt(-CN) 4 ]. 24 Most studies of spin-crossover applications use one of those iron(II) materials, or a derivative of them.…”