Spin‐State Modulation in Fe^II‐Based Hofmann‐Type Coordination Polymers: From Molecules to Materials

Abstract

Spin crossover complexes that reversibly interconvert between two stable states imitate a binary state of 0 and 1, delivering a promising possibility to address the data processing concept in smart materials. Thus, a comprehensive understanding of the modulation of magnetic transition between high spin and low spin and the factors responsible for stabilizing the spin states is an essential theme in modern materials design. In this context, the present review attempts to provide a concise outline of the design strategy employed at the molecular level for fine-tuning the spin-state switching in Fe II -based Hofmann-type coordination polymers and their effects on the optical and magnetic response. In addition, development towards the nanoscale architectures of HCPs, i. e., in terms of nanoparticles and thin films, are emphasized to bridge the gap between the laboratory and reality.

Pressure-Induced Hysteretic and Abrupt Spin Transition in Amine Functionalized Isoquinoline-Based Two-Dimensional FeII Hofmann Frameworks

“…In the cooling cycle, the magnetic susceptibility plot did not superimpose on the heating cycle, which indicates the presence of a hysteresis loop. With lowering of the temperature, χ M T attains a value of 3.51 mol −1 K cm 3 , which remains constant in the temperature range of 300−210 K. Upon a further decrease in temperature, the susceptibility suddenly drops to a value close to zero at 200 K. The derivative plot of magnetic susceptibility data reveals a hysteretic loop of 7 K, with cooling and heating transition temperatures, 208 K (T ↓ 1/2 ) and 215 K (T ↑ 1/2 ) respectively. A similar magnetic susceptibility curve has been observed for 1Pd with an increase in the transition temperature.…”

“…Variable-temperature (VT) magnetic susceptibility measurements were performed on a bulk crystalline sample of 1Pt at a scan rate of 1 K min −1 and in the temperature range of 2−300 K. The magnetic properties have been expressed as the product χ M T, where χ M is the molar magnetic susceptibility and T is the temperature, as displayed in Figure 2, revealing a one-step spin crossover behavior. In the low-temperature region (2−205 K), the molar magnetic susceptibility value is 0.2 mol −1 K cm 3 , and the value remains constant until 205 K indicating the presence of Fe II in the LS state. On further heating, the magnetic susceptibility value abruptly increases to 3.51 mol −1 K cm 3 at 210 K and remains constant on further heating until 300 K, indicating the 100% conversion of Fe II centers from the LS to HS state.…”

An iron(II) complex shows bistable spin-state switching characteristic with T1/2 centred at room temperature

“…Finally, the grand old phenomenon of SCO continues to evolve keeping abreast with the contemporary developments in molecular magnetism and related topics. 5,[28][29][30][31][32][33][34][35][36][37][38][39] We are happy that the topic has chosen us to express interesting facets, as discussed in this script.…”

Iron(II) Mediated Supramolecular Architectures with Schiff Bases and Their Spin-Crossover Properties

“…Hence, the designing of hysteretic SCO materials for specific application requires controlling of the interactions in metal ion switching sites in the architecture. Materials that exhibit large SCO hysteresis are mostly molecular complexes [ 39 , 40 , 41 ], and many of the compounds are iron(II) complexes of N-donor ligands such as Schiff bases that are suited to cooperative spin transitions as they show large structural differences between HS and LS states [ 42 , 43 , 44 ].…”