Polymorphism in spin-crossover systems

Abstract

The occurrence of spin-crossover (SCO) highly depends on external influences, i.e. temperature, pressure, light irradiation or magnetic field, this electronic switching phenomenon is accompanied by drastic changes in magnetic and optical properties, dielectric constants, colour and structures. Thus, SCO materials are particularly attractive for potential applications in molecular sensing, switching, data storage, display, and other electronic devices at nanometric scale. Polymorphism is widely encountered in the studies of crystallization, phase transition, materials synthesis, biomineralization, and in the manufacture of drugs. Because different crystal forms of the same substance can possess very different properties and behave as different materials, so they are particularly meaningful for investigating SCO phenomena. Studying polymorphism of SCO compounds is therefore important for better understanding the structural factors contributing to spin transition and the structure-function relationship. This critical review is aimed to provide general readers with a comprehensive view of polymorphism in SCO systems. The article is generally structured according to specific metal ions and the dimensionality of compounds in the field. This paper is addressed to readers who are interested in multifunctional materials and tuning magnetic properties through supramolecular chemistry principles (129 references).

A High Pressure Investigation of the Order-Disorder Phase Transition and Accompanying Spin Crossover in [FeL12](ClO4)2 (L1 = 2,6-bis{3-methylpyrazol-1-yl}-pyrazine)

“…More generally, hydrostatic pressure can be used as a tool to probe structure-property correlations, often modifying crystallographic phase transitions and tuning intermolecular interactions without changing the chemical connectivity of the material. The latter point is particularly pertinent in the case of molecular SCO materials where both the chemical connectivity and the intermolecular interactions have strong influence on properties: small changes in chemistry of ligands can significantly alter switching properties, while different polymorphs of the same molecule can show vastly different SCO properties [15]. Pressure has also been used to decouple crystallographic phase transitions from SCO properties in order to probe their interrelationship [16].…”

Surface induces different crystal structures in a room temperature switchable spin crossover compound

“…[1][2][3][4][5] This setback, which manifests itself in phenomena such as polymorphism and solvatomorphism, is particularly relevant in the drug industry; however, it is common in many materials, such as organic semiconductors, 6,7 supramolecular systems 1 and spin crossover (SCO) compounds. 5,[8][9][10][11][12][13][14][15][16][17][18][19][20] Despite some exceptions, in which polymorphism is exploited as an advantageous property, [21][22][23][24] usually it is thought to be a drawback for many technological applications, which often compromises the development of materials. On the contrary, gaining a detailed knowledge of different crystal forms and their influence on the functionalities can be the manner to select the best performing phase.…”

“…), the crystal structure have a crucial impact on SCO properties. 5 SCO compounds are processable by conventional 34 or unconventional methods [35][36][37][38] and were proposed for several applications ranging from permanent/rewritable information storage and spintronic 27,[39][40][41] to chemical actuators, 42 multimodal sensors 43 of chemicals 44,45 and pressure sensors. 46 Several exhaustive reviews encompass the synthesis, properties and applications of SCO compounds.…”

Disclosing the Ligand- and Solvent-Induced Changes on the Spin Transition and Optical Properties of Fe(II)-Indazolylpyridine Complexes

“…Consequently, dense networks have been designed in order to enhance cooperativity by means of strong covalent [6,7] or van der Waals interactions [8][9][10] between SCO molecules. However, even if few remarkable computational studies have dealt with the effect of crystal packing and cooperativity on SCO materials [11,12], (including phenomenological models [13,14]) progress in the field has been hindered by the difficulty of establishing general structure-function correlations in the solid state, which should incorporate the effect of counterions and solvent molecules beyond the SCO molecules itself (not to mention the importance of polymorphism [15,16]). …”