scholarly journals Elastic Modeling of Two-Step Transitions in Sterically Frustrated 1D Binuclear Spin-Crossover Chains

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1836
Author(s):  
Rachid Traiche ◽  
Hassane Oubouchou ◽  
Kamel Boukheddaden
Keyword(s):  
Spin State ◽  
Spin Crossover ◽  
Spin Transition ◽  
Large Family ◽  
Relaxation Dynamics ◽  
Thermal Dependence ◽  
Competing Interactions ◽  
Open Chain ◽  
Self Organized ◽  
Binuclear Unit

Among the large family of spin-crossover materials, binuclear systems play an important role due to their specific molecular configurations, allowing the presence of multi-step transitions and elastic frustration. Although this issue benefited from a significant number of spin-based theories, there is almost no elastic description of the spin transition phenomenon in binuclear systems. To overcome this deficiency, in this work we develop the first elastic modeling of thermal properties of binuclear spin-crossover solids. At this end, we investigated a finite spin-crossover open chain constituted of elastically coupled binuclear (A = B) blocks, ⋯A=B−A=B−A=B⋯, in which the considered equivalent A and B sites may occupy two configurations, namely low-spin (LS) and high-spin (HS) states. The sites of the binuclear unit interact via an intramolecular spring and couple to the neighboring binuclear units via other springs. The model also includes the change of length inside and between the binuclear units subsequent to the spin state changes. When injecting an elastic frustration inside the binuclear unit in the LS state, competing interactions between the intra- and the inter-binuclear couplings emerge. The latter shows that according to the intra- and inter-binuclear elastic constants and the strength of the frustration, multi-step transitions are derived, for which a specific self-organization of type (HS = HS)-(LS-LS)-(HS = HS)⋯ is revealed and discussed. Finally, we have also studied the relaxation of the metastable photoinduced HS states at low temperature, in which two relaxation regimes with transient self-organized states were identified when monitoring the elastic frustration rate or the ratio of intra- and intermolecular elastic interactions. These behaviors are reminiscent of the thermal dependence of the order parameters of the system. The present model opens several possibilities of extensions of elastic frustrations acting in polynuclear spin-crossover systems, which may lead to other types of spin-state self-organizations and relaxation dynamics.

scholarly journals Spin state switching in iron coordination compounds

2013 ◽  
Vol 9 ◽  
pp. 342-391 ◽  
Author(s):  
Philipp Gütlich ◽  
Ana B Gaspar ◽  
Yann Garcia
Keyword(s):  
Spin State ◽  
Coordination Compounds ◽  
Spin Crossover ◽  
Spin Transition ◽  
Pressure Sensors ◽  
Ligand Field ◽  
Thermally Induced ◽  
Practical Applications ◽  
State Switching ◽  
Switching Phenomenon

The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors as well as optical devices. The article begins with a brief description of the principle of molecular spin state switching using simple concepts of ligand field theory. Conditions to be fulfilled in order to observe spin crossover will be explained and general remarks regarding the chemical nature that is important for the occurrence of spin crossover will be made. A subsequent section describes the molecular consequences of spin crossover and the variety of physical techniques usually applied for their characterization. The effects of light irradiation (LIESST) and application of pressure are subjects of two separate sections. The major part of this account concentrates on selected spin crossover compounds of iron(II), with particular emphasis on the chemical and physical influences on the spin crossover behavior. The vast variety of compounds exhibiting this fascinating switching phenomenon encompasses mono-, oligo- and polynuclear iron(II) complexes and cages, polymeric 1D, 2D and 3D systems, nanomaterials, and polyfunctional materials that combine spin crossover with another physical or chemical property.

Frequency Dependent Charge Transport and Spin State Switching Characteristics of Fe(phen)2(NCS)2 in Polymer

2020 ◽  
Vol 20 (5) ◽  
pp. 2803-2812
Author(s):  
Chaitali Mondal ◽  
M. L. Nanda Goswami ◽  
Swapan K. Mandal
Keyword(s):  
Charge Transport ◽  
Spin State ◽  
Ac Conductivity ◽  
Spin Transition ◽  
Hysteresis Loops ◽  
State Dependence ◽  
Temperature Dependent ◽  
Thermal Dependence ◽  
The Difference ◽  
Composite Samples

We report on the bistability in spin states of spin crossover (SCO) compound Fe(phen)2(NCS)2 in polymer (polypyrrole) by frequency (1–100 kHz) and temperature dependent (305–457 K) electrical conductivity measurements. The structure and growth of SCO compounds in conducting polymer are obtained by scanning electron microscopy, X-ray diffraction and optical absorption measurements. The thermal dependence of ac conductivity σ(ω) shows the clear formation of a hysteresis loop in its cooling and heating cycle due to the difference in conductivity in high spin and low spin state. The size, shape and width of the hysteresis loops are found to be critically dependent on the applied frequency and/or the ratio between SCO and polymer. The ac conductivity is found to exhibit a dispersive behavior following Jonscher’s law: σ(ω) ∝ ωn below a critical frequency ωc, above which it is found to monotonically decrease with increasing frequency. The thermal dependence of the exponent n and ωc is also explored. The charge transport phenomena are explained in the framework of hopping of charge carriers. The data reveals that addition of polymer can play an important role to tune the conductivity of SCO compounds and its spin state dependence characteristics which may be quite helpful for fabricating future spin-based devices. Temperature dependent magnetic susceptibility measurement also confirms the spin transition behavior of the SCO/ppy composite samples. These SCO/ppy composite samples can be taken as the reliable nanomaterials fabricated with the concept of future spin based nanoarchitectonics.

scholarly journals Structure:function relationships for thermal and light-induced spin-crossover in isomorphous molecular materials

2020 ◽  
Vol 8 (25) ◽  
pp. 8420-8429
Author(s):  
Rafal Kulmaczewski ◽  
Elzbieta Trzop ◽  
Eric Collet ◽  
Sergi Vela ◽  
Malcolm A. Halcrow
Keyword(s):  
High Spin ◽  
Spin State ◽  
Spin Crossover ◽  
Spin Transition ◽  
Molecular Materials

The complicated light-induced spin state trapping behaviour of a family of isomorphous solvate crystals reflects reorientation of the lattice solvent during the spin-transition (white = high-spin, brown = low-spin).

scholarly journals Thermal Spin Crossover in Fe(II) and Fe(III). Accurate Spin State Energetics at the Solid State

2019 ◽  
Author(s):  
Sergi Vela ◽  
Maria Fumanal ◽  
Jordi Cirera ◽  
Jordi Ribas
Keyword(s):  
Solid State ◽  
Spin State ◽  
Metal Ion ◽  
Density Functional ◽  
Spin Crossover ◽  
Spin Transition ◽  
Computational Modelling ◽  
Dispersion Correction ◽  
Correction Scheme ◽  
The Impact

<p>The thermal Spin Crossover (SCO) phenomenon refers to an entropy-driven spin transition in some materials based on d<sub>6</sub>-d<sub>9</sub> transition metal complexes. While its molecular origin is well known, intricate SCO behaviours are increasingly common, in which the spin transition occurs concomitantly to <i>e.g.</i> phase transformations, solvent absorption/desorption, or order-disorder processes. The computational modelling of such cases is challenging, as it requires accurate spin state energies in the solid state. Density Functional Theory (DFT) is the best framework, but most DFT functionals are unable to balance the spin state energies. While few hybrid functionals perform better, they are still too expensive solid-state minima searches in moderate-size systems. The best alternative is to dress cheap local (LDA) or semi-local (GGA) DFT functionals with a Hubbard-type correction (DFT+<i>U</i>). However, the parametrization of U is not straightforward due to the lack of reference values, and because ab initio parametrization methods perform poorly. Moreover, SCO complexes undergo notable structural changes upon transition, so intra- and inter-molecular interactions might play an important role in stabilizing either spin state. As a consequence, the U parameter depends strongly on the dispersion correction scheme that is used. In this paper, we parametrize U for nine reported SCO compounds (five based on Fe<sup>II</sup>, <b>1</b>-<b>5</b> and four based on Fe<sup>III</sup>, <b>6</b>-<b>9</b>) when using the D3 and D3-BJ dispersion corrections. We analyze the impact of the dispersion correction treatments on the SCO energetics, structure, and the unit cell dimensions. The average U values are different for each type of metal ion (Fe<sup>II</sup> vs. Fe<sup>III</sup>), and dispersion correction scheme (D3 vs. D3-BJ) but they all show excellent transferability, with mean absolute errors (MAE) below chemical accuracy (i.e. MAE < 4 kJ/mol). This enables a better description of SCO processes and, more generally, of spin state energetics, in materials containing Fe<sup>II</sup> and Fe<sup>III</sup> ions.</p>

scholarly journals Structural studies of a flexible 2D layer spin crossover coordination polymer

2014 ◽  
Vol 70 (a1) ◽  
pp. C1238-C1238
Author(s):  
Yu-Chun Chuang ◽  
Chung-Kai Chang ◽  
Ching-Che Kao ◽  
Jey-Jau Lee ◽  
Chih-Chieh Wang
Keyword(s):  
Magnetic Property ◽  
Spin State ◽  
Spin Crossover ◽  
Layer Structure ◽  
Dominant Role ◽  
Spin Transition ◽  
High Spin State ◽  
Structural Studies ◽  
Synchrotron Powder Diffraction ◽  
Solvent Molecules

The first coordination sphere of spin crossover material has been comprehended to play a dominant role to its magnetic property. However, the intermolecular interactions, such as π···π interaction and hydrogen bonding, also play a crucial factor. The contents of the solvent in a 2D layer structure, Fe (μ-atrz)(μ-pyz)(NCS)2·nH2O where n=4, 2 and 0, has been reported to be able to affect the spin transition behavior dramatically.[1] As loss of solvent molecules, the inter-layer distance becomes shorter and the transition temperature shifts to lower temperature and accompanies a larger hysteresis loop. To further understand the correlation between the inter-layer distance and magnetic property, the guest ab/desorption and pressure-induced synchrotron powder diffraction experiments were performed at BL01C2 in NSRRC. Based on the cyclic TGA measurements, the guest molecules, H2O, MeOH and EtOH, all can be removed and retaken repeatedly. The pressure-induced PXRD experiment was performed using a Boehler-Almax design diamond anvil cell (DAC). The detail structural studies attempt to understand not only the spin state changes from HS (high spin state) to LS (low spin state) but also the cooperative effect through the inter-layer distance.

scholarly journals Thermal Spin Crossover in Fe(II) and Fe(III). Accurate Spin State Energetics at the Solid State

2019 ◽  
Author(s):  
Sergi Vela ◽  
Maria Fumanal ◽  
Jordi Cirera ◽  
Jordi Ribas
Keyword(s):  
Solid State ◽  
Spin State ◽  
Metal Ion ◽  
Density Functional ◽  
Spin Crossover ◽  
Spin Transition ◽  
Computational Modelling ◽  
Dispersion Correction ◽  
Correction Scheme ◽  
The Impact

<p>The thermal Spin Crossover (SCO) phenomenon refers to an entropy-driven spin transition in some materials based on d<sub>6</sub>-d<sub>9</sub> transition metal complexes. While its molecular origin is well known, intricate SCO behaviours are increasingly common, in which the spin transition occurs concomitantly to <i>e.g.</i> phase transformations, solvent absorption/desorption, or order-disorder processes. The computational modelling of such cases is challenging, as it requires accurate spin state energies in the solid state. Density Functional Theory (DFT) is the best framework, but most DFT functionals are unable to balance the spin state energies. While few hybrid functionals perform better, they are still too expensive solid-state minima searches in moderate-size systems. The best alternative is to dress cheap local (LDA) or semi-local (GGA) DFT functionals with a Hubbard-type correction (DFT+<i>U</i>). However, the parametrization of U is not straightforward due to the lack of reference values, and because ab initio parametrization methods perform poorly. Moreover, SCO complexes undergo notable structural changes upon transition, so intra- and inter-molecular interactions might play an important role in stabilizing either spin state. As a consequence, the U parameter depends strongly on the dispersion correction scheme that is used. In this paper, we parametrize U for nine reported SCO compounds (five based on Fe<sup>II</sup>, <b>1</b>-<b>5</b> and four based on Fe<sup>III</sup>, <b>6</b>-<b>9</b>) when using the D3 and D3-BJ dispersion corrections. We analyze the impact of the dispersion correction treatments on the SCO energetics, structure, and the unit cell dimensions. The average U values are different for each type of metal ion (Fe<sup>II</sup> vs. Fe<sup>III</sup>), and dispersion correction scheme (D3 vs. D3-BJ) but they all show excellent transferability, with mean absolute errors (MAE) below chemical accuracy (i.e. MAE < 4 kJ/mol). This enables a better description of SCO processes and, more generally, of spin state energetics, in materials containing Fe<sup>II</sup> and Fe<sup>III</sup> ions.</p>

scholarly journals Spin transition and relaxation dynamics coupled to a crystallographic phase transition in a polymeric iron(II) spin-crossover system

2008 ◽  
Vol 455 (4-6) ◽  
pp. 192-196 ◽  
Author(s):  
Itana Krivokapic ◽  
Cristian Enachescu ◽  
Robert Bronisz ◽  
Andreas Hauser
Keyword(s):  
Phase Transition ◽  
Spin Crossover ◽  
Spin Transition ◽  
Relaxation Dynamics

Isomorphism between the electro-elastic modeling of the spin transition and Ising-like model with competing interactions: Elastic generation of self-organized spin states

2021 ◽  
Vol 129 (15) ◽  
pp. 153901
Author(s):  
Mamadou Ndiaye ◽  
Yogendra Singh ◽  
Houcem Fourati ◽  
Mouhamadou Sy ◽  
Bassirou Lo ◽  
...  
Keyword(s):  
Spin Transition ◽  
Spin States ◽  
Competing Interactions ◽  
Self Organized

scholarly journals Spin-Crossover 2-D Hofmann Frameworks Incorporating an Amide-Functionalized Ligand: N-(pyridin-4-yl)benzamide

Chemistry ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 360-372
Author(s):  
Xandria Ong ◽  
Manan Ahmed ◽  
Luonan Xu ◽  
Ashley T. Brennan ◽  
Carol Hua ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Spin State ◽  
Spin Crossover ◽  
Variable Temperature ◽  
Spin Transition ◽  
Single Step ◽  
Amide Group ◽  
State Transitions ◽  
Structure Property ◽  
Scanning Calorimetry

Two analogous 2-D Hofmann-type frameworks, which incorporate the novel ligand N-(pyridin-4-yl)benzamide (benpy) [FeII(benpy)2M(CN)4]·2H2O (M = Pd (Pd(benpy)) and Pt (Pt(benpy))) are reported. The benpy ligand was explored to facilitate spin-crossover (SCO) cooperativity via amide group hydrogen bonding. Structural analyses of the 2-D Hofmann frameworks revealed benpy-guest hydrogen bonding and benpy-benpy aromatic contacts. Both analogues exhibited single-step hysteretic spin-crossover (SCO) transitions, with the metal-cyanide linker (M = Pd or Pt) impacting the SCO spin-state transition temperature and hysteresis loop width (Pd(benpy): T½↓↑: 201, 218 K, ∆T: 17 K and Pt(benpy): T½↓↑: 206, 226 K, ∆T: 20 K). The parallel structural and SCO changes over the high-spin to low-spin transition were investigated using variable-temperature, single-crystal, and powder X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. These studies indicated that the ligand–guest interactions facilitated by the amide group acted to support the cooperative spin-state transitions displayed by these two Hofmann-type frameworks, providing further insight into cooperativity and structure–property relationships.

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