Spin‐Crossover Tuned Rotation of Pyrazolyl Rings in a 2D Iron(II) Complex towards Synergetic Magnetic and Dielectric Transitions

Abstract

Materials showing synergy of magnetic and dielectric transitions are promising candidates for future molecular devices. The challenge is how to realize synergy between spin and dielectric transitions with responses to external stimuli. Herein, we design a 2D spin crossover (SCO) complex, [Fe II (dpa)][(pzTp)Fe III -(CN) 3 ] 2 (1) (dpa = 1,2-bis(4-pyridyl)ethyne and pzTp = tetrakis(pyrazolyl)borate). The local structural changes about the Fe II ion were propagated to the whole crystal through the rigid bridging ligands (dpa), leading to elastic interactions to realize the abrupt SCO and rotational movements of polar apical pyrazolyl rings in the [(pzTp)Fe III (CN) 3 ] À units. Dielectric measurements confirmed a substantial dielectric change (Δɛ' = 2.3) upon the spin transition. This work provides a rational strategy to couple the spin transition and rotation of polar components, which is crucial for the synergetic switch of magnetism and dielectricity.

Simultaneous magneto-dielectric transitions in a fluorescent Hofmann-type coordination polymer

“…44,45 This means that the coordination geometry for the Fe II center was significantly changed upon the spin transition, compared with reported SCO complexes showing dielectric transition properties. 14,46 These structural changes would inevitably cause geometric changes in charge distribution and the electric dipole of the local Fe-centered coordination sphere. In addition, the rearrangement of 3d electrons in t 2g and e g orbitals affects the chemical bonding interactions and polarizations.…”

“…47,48 It should be noted that the extended layer structure can more effectively achieve simultaneous magneto-dielectric transitions than those of discrete mono-and dinuclear SCO complexes. 14,49 This can be explained by the fact that the local variations of the Fe II centers and the elastic interactions between SCO centers can be propagated to the whole crystal structure through the bridging linkers, 35,50 which are different from those in discrete mono-and dinuclear SCO complexes, where the van der Waals interactions play the dominant role. This leads to the enhanced cooperativity of Fe II centers and efficient magneto-dielectric switching.…”

“…9,10 In recent years, considerable progress has been achieved in developing bifunctional materials that combine SCO with a certain property, such as luminescence, dielectricity, conductivity, or chirality. [11][12][13][14][15][16] However, the integration of multiple properties into one material remains a hard task. This difficulty arises from the fact that several properties are governed by the substituent or molecular units (e.g., chirality, SCO, and luminescence), while others depend on the molecular arrangements and packings (e.g., porosity, ferroelectricity, and ferromagnetism).…”

Structural phase transition and dielectric responses in two novel cyano-bridged coordination polymers synthesized by sealing the incomplete cyano-bridged cage

“…Switchable molecular materials possess two or more different phases, which can be driven from one phase to another phase by complex external stimuli, such as temperature, pressure, light, magnetism and so on. [1][2][3][4] When a phase transition occurs, the materials' physical properties including nonlinear optical properties, dielectric properties and magnetic pro-perties may also change, which allows their use as sensors, memory devices, switches, etc. [5][6][7] Compared with traditional pure organic/inorganic materials, organic-inorganic hybrid materials have greater potential to change the internal molecular arrangement and act as a temperature responsive phase transition material.…”

Magnetic and Dielectric Switchings Actuated by the Rotation of the Picoline Ligand in an Iron-Based Dinuclear Phase-Transition Complex

“…One of the intriguing physical properties that associates with lattice variation is dielectric switching wherein the dielectric constant of materials can be interconverted between the high-value and low-value states. Such a shift in the electric susceptibility is conceptionally parallel to magnetic switching, providing a new avenue to prepare molecular materials with switchable properties. − However, it remains difficult to realize synergetic magnetic and dielectric switches in a molecular material.…”