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José Antonio Real - One of the best experts on this subject based on the ideXlab platform.
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Thermochromic Meltable Materials with Reverse Spin Transition Controlled by Chemical Design.
Angewandte Chemie (International ed. in English), 2020Co-Authors: Francisco Javier Valverde-muñoz, Maksym Seredyuk, M. Carmen Muñoz, Gábor Molnár, Yurii S. Bibik, José Antonio RealAbstract:We report a series of meltable FeII complexes, which, depending on the length of aliphatic chains, display abrupt forward low-Spin to high-Spin Transition or unprecedented melting-triggered reverse high-Spin to low-Spin Transition on temperature rise. The reverse Spin Transition is perfectly reproducible on thermal cycling and the obtained materials are easily processable in the form of thin film owing to their soft-matter nature. We found that the discovered approach represents a potentially generalizable new avenue to control both the location in temperature and the direction of the Spin Transition in meltable compounds.
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Variable Cooperative Interactions in the Pressure and Thermally Induced Multistep Spin Transition in a Two-Dimensional Iron(II) Coordination Polymer
Inorganic chemistry, 2020Co-Authors: Mengyun Yuan, Maksym Seredyuk, G. G. Levchenko, Ludmila Berezhnaya, Hennagii Fylymonov, Ana B. Gaspar, José Antonio RealAbstract:Two types of experiments conducted to investigate the effect of pressure on the Spin crossover (SCO) properties of the 2D Fe(II) coordination polymer formulated {Fe[bipy(ttr)2]}n are reported, namely, (1) magnetic measurements performed at variable temperature and at fixed pressure and (2) visible spectroscopy at variable pressure and fixed temperature. The magnetic experiments carried out under a hydrostatic pressure constraint of 0.04, 0.08, and 0.8 GPa reveal a two-step Spin Transition behavior. The characteristic critical temperatures of the Spin Transition are shifted upward in temperature as pressure increases. The slope of the straight-line of the Tc vs P plot, dTc/dP, is 775 K/GPa and 300 K/GPa, for the high temperature and the low temperature steps, respectively. These values are remarkably large and denote the extreme sensitivity of the material to the application of pressure. Indeed, the visible spectroscopic measurements performed at 293 K show that a complete Spin Transition is induced at pressures as low as 0.4 GPa. Moreover, the pressure-induced Spin Transition is reversible and shows an asymmetric hysteresis. An analysis of the cooperative interactions of the thermal- and pressure-induced Spin Transition in the framework of the model of elastic interactions reveals that the elastic energy of the lattice as well as the interaction parameter between the SCO centers change during the course of the Spin Transition. Consequently, the character of the Spin Transition varies from abrupt for the high temperature step to continuous for the low temperature step.
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exploiting pressure to induce a guest blocked Spin Transition in a framework material
Inorganic Chemistry, 2016Co-Authors: Natasha F Sciortino, José Antonio Real, Florence Ragon, Katrina A Zenere, Peter D Southon, Gregory J Halder, Karena W Chapman, Lucia Pineirolopez, Cameron J Kepert, Suzanne M NevilleAbstract:A new functionalized 1,2,4-triazole ligand, 4-[(E)-2-(5-methyl-2-thienyl)vinyl]-1,2,4-triazole (thiome), was prepared to assess the broad applicability of strategically producing multistep Spin Transitions in two-dimensional Hofmann-type materials of the type [FeIIPd(CN)4(R-1,2,4-trz)2]·nH2O (R-1,2,4-trz = a 4-functionalized 1,2,4-triazole ligand). A variety of structural and magnetic investigations on the resultant framework material [FeIIPd(CN)4(thiome)2]·2H2O (A·2H2O) reveal that a high-Spin (HS) to low-Spin (LS) Transition is inhibited in A·2H2O due to a combination of guest and ligand steric bulk effects. The water molecules can be reversibly removed with retention of the porous host framework and result in the emergence of an abrupt and hysteretic one-step Spin Transition due to the removal of guest internal pressure. A Spin Transition can, furthermore, be induced in A·2H2O (0–0.68 GPa) under hydrostatic pressure, as evidenced by variable-pressure structure and magnetic studies, resulting in a two-s...
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Exploiting Pressure To Induce a “Guest-Blocked” Spin Transition in a Framework Material
Inorganic chemistry, 2016Co-Authors: Natasha F Sciortino, José Antonio Real, Florence Ragon, Katrina A Zenere, Peter D Southon, Gregory J Halder, Karena W Chapman, Cameron J Kepert, Lucía Piñeiro-lópez, Suzanne M NevilleAbstract:A new functionalized 1,2,4-triazole ligand, 4-[(E)-2-(5-methyl-2-thienyl)vinyl]-1,2,4-triazole (thiome), was prepared to assess the broad applicability of strategically producing multistep Spin Transitions in two-dimensional Hofmann-type materials of the type [FeIIPd(CN)4(R-1,2,4-trz)2]·nH2O (R-1,2,4-trz = a 4-functionalized 1,2,4-triazole ligand). A variety of structural and magnetic investigations on the resultant framework material [FeIIPd(CN)4(thiome)2]·2H2O (A·2H2O) reveal that a high-Spin (HS) to low-Spin (LS) Transition is inhibited in A·2H2O due to a combination of guest and ligand steric bulk effects. The water molecules can be reversibly removed with retention of the porous host framework and result in the emergence of an abrupt and hysteretic one-step Spin Transition due to the removal of guest internal pressure. A Spin Transition can, furthermore, be induced in A·2H2O (0–0.68 GPa) under hydrostatic pressure, as evidenced by variable-pressure structure and magnetic studies, resulting in a two-s...
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Imparting hysteretic behavior to Spin Transition in neutral mononuclear complexes
RSC Advances, 2016Co-Authors: Maksym Seredyuk, M. Carmen Muñoz, Kateryna O. Znovjyak, Yurii Galyametdinov, Igor O. Fritsky, José Antonio RealAbstract:A series of Spin Transition neutral compounds [FeL(NCS)2] has been synthesized and characterized by means of magnetic susceptibility studies, X-ray diffraction, IR and Mossbauer spectroscopic, and calorimetric measurements (L = N,N-bis((3-alkoxypyridin-2-yl)methylene)-propane-1,3-diamine, number of carbon atoms in chains (n) = 4, 12, 14, 16, 18, 20). The shortest chain compound is crystalline and displays a gradual Spin Transition above ambient temperature. Growing the aliphatic substituent up to n = 12 and 14 leads to loss of crystalline order and deterioration of magnetic properties. At the critical chain length n = 16 and above, the compounds undergo a phase Transition reflected by a Spin Transition and resulting in the appearance of susceptibility hysteresis initially not observed for the short chain congener. For the compound with n = 20, hysteresis becomes the most pronounced. The study shows the importance of chain length optimization for effective feedback between phase and Spin Transitions.
Yann Garcia - One of the best experts on this subject based on the ideXlab platform.
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Cooperative Spin Transition in a lipid layer like system.
Chemical communications (Cambridge, England), 2011Co-Authors: Stephan Schlamp, Anil D Naik, Birgit Weber, Yann GarciaAbstract:A novel iron(II) mononuclear Spin Transition complex [FeL(py)(2)] displays an abrupt Spin Transition around 225 K accompanied by a very wide thermal hysteresis loop (?50 K) that spreads out over 100 K. Crystal structure analysis in both low-Spin and high-Spin states reveals a lipid layer-like arrangement of the complex molecules and provides insights into the Spin switching mechanism.
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Spin Transition charted in a fluorophore-tagged thermochromic dinuclear iron(II) complex
Journal of the American Chemical Society, 2011Co-Authors: Yann Garcia, Sébastien Michotte, Anil D Naik, Guangyuan Zhou, Koen Robeyns, François Robert, Bernard Tinant, Luc PirauxAbstract:The first crystal structures of a dinuclear iron(II) complex with three N1,N2-1,2,4-triazole bridges in the high-Spin and low-Spin states are reported. Its sharp Spin Transition, which was probed using X-ray, calorimetric, magnetic, and (57)Fe Mossbauer analyses, is also delineated in the crystalline state by variable-temperature fluorimetry for the first time.
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Spin Transition in [Fe(phen)2(NCS)2]- μSR study
Physica Status Solidi (a), 2004Co-Authors: Yann Garcia, Vadim Ksenofontov, Stewart J Campbell, James S. Lord, Yves Boland, P. GütlichAbstract:The reversible thermal Spin Transition which occurs in [Fe(phen) 3 (NCS) 2 ) around T 1/2 ∼ 177 K has been investigated by muon Spin relaxation (μSR) (-10-280 K). The depolarisation curves are well described by two Lorentzian lines represent fast and slow components in the decay curves, with the initial asymmetry parameter of the fast component found to track the Spin Transition in [Fe(phen) 2 (NCS) 2 ]. Comparison of zero-field and transverse field (20 Oe) μSR measurements shows that diamagnetic muonic species occur over the entire temperature range.
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Spin Transition in [Fe(phen)2(NCS)2] - SR study
physica status solidi (a), 2004Co-Authors: Yann Garcia, Vadim Ksenofontov, Stewart J Campbell, James S. Lord, Yves Boland, P. GtlichAbstract:The reversible thermal Spin Transition which occurs in [Fe(phen)2(NCS)2] around T1/2 ∼ 177 K has been investigated by muon Spin relaxation (µSR) (∼10–280 K). The depolarisation curves are well described by two Lorentzian lines represent fast and slow components in the decay curves, with the initial asymmetry parameter of the fast component found to track the Spin Transition in [Fe(phen)2(NCS)2]. Comparison of zero-field and transverse field (20 Oe) µSR measurements shows that diamagnetic muonic species occur over the entire temperature range. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Spin Transition in [Fe(phen)(2)(NCS)(2)] - mu SR study
Physica Status Solidi (a), 2004Co-Authors: Yann Garcia, Stewart J Campbell, James S. Lord, Yves Boland, Ksenofontov, P. GütlichAbstract:The reversible thermal Spin Transition which occurs in [Fe(phen)(2)(NCS)(2)] around T-1/2 similar to 177 K has been investigated by muon Spin relaxation (muSR) (similar to10-280 K). The depolarisation curves are well described by two Lorentzian lines represent fast and slow components in the decay curves, with the initial asymmetry parameter of the fast component found to track the Spin Transition in [Fe(phen)2(NCS),]. Comparison of zero-field and transverse field (20 Oe) muSR measurements shows that diamagnetic muonic species occur over the entire temperature range.
Jean-françois Létard - One of the best experts on this subject based on the ideXlab platform.
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Neutron powder diffraction studies of two Spin Transition Fe(II)-complexes under pressure
Journal of Applied Crystallography, 2008Co-Authors: Vincent Legrand, Philippe Guionneau, Frédéric Le Gac, Jean-françois LétardAbstract:The pressure dependences of the lattice parameters of two Spin Transition compounds have been derived from neutron powder diffraction measurements at ambient temperature. The study of Fe(PM–AzA)2(NCS)2 [PM is N-20-pyridylmethylene and AzA is 4-(phenylazo)aniline] has been used to validate this new type of investigation of Spin crossover compounds, and the study of Fe(PM–BiA)2(NCS)2 (BiA is 4-aminobiphenyl) has allowed the atypical Spin crossover behaviour of this compound under pressure to be explained. In addition, this complex exhibits a pressure-induced structural Transition with an associated symmetry change, inducing the transformation of Fe(PM–BiA)2-(NCS)2 into a different polymorph that avoids a first-order Spin Transition in favour of continuous Transition.
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Stepwise Spin Transition in a mononuclear iron(II) complex with unusually wide plateau
European Journal of Inorganic Chemistry, 2008Co-Authors: Birgit Weber, Chiara Carbonera, Cédric Desplanches, Jean-françois LétardAbstract:The reaction of the Schiff-base like ligand H2L [L2- = (E,E)-({diethyl 2,2-[1,2-phenylenebis(iminomethylidyne)]bis(3-oxobutanato)})] with iron(II) acetate in methanol in the presence of 4-cyanopyridine leads to the formation of an octahedral iron(II) complex with the formula FeL(CNpy)2·0.25CNpy (1). The magnetic properties of this complex were investigated using temperature-dependent susceptibility measurements (SQUID) and Mössbauer spectroscopy. Both measurements indicate that the complex performs a stepwise Spin Transition with a large plateau in the region from 225 K to 125 K and HS 0.25. The molecule structure of the compound was determined at room temperature, 240 K (HS 0.5 according to susceptibility measurements) and 100 K. Two complex molecules were found in the asymmetric unit with strong - interactions between the phenylene rings of H2L. In agreement with outcomes from the magnetic measurements, both iron centres are in the high-Spin state at room temperature and in the low-Spin state at 100 K. At 240 K one of the two iron centres is high-Spin and the other one low-Spin. The reason for the wide step with one fourth of the iron centres in the high-Spin state is the additional distorted 4-cyanopyridine in the crystal that influences the Transition temperature of the surrounding iron centres. The Spin Transition was followed in solution by using 1H NMR spectroscopy. A gradual Spin Transition with T1/2 = 238 K is obtained. Temperature-dependent diffuse reflectivity spectra show the occurrence of photoconversion at the surface of the sample but only about 6 % of the complex could be switched in bulk condition using a SQUID magnetometer and the stability of the photoinduced HS state with TLIESST = 40 K is very weak.
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Effect of metal dilution on the light-induced Spin Transition in [FexZn1-x(phen)2(NCS)2] (phen = 1,10-phenanthroline)
Dalton Transactions, 2008Co-Authors: Cherif Baldé, Philipp Gütlich, Philippe Guionneau, Cédric Desplanches, Alain Wattiaux, Jean-françois LétardAbstract:The thermal and light-induced Spin Transitions in [FexZn1-x(phen)2(NCS)2] (phen = 1,10-phenantholine) have been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal Spin Transition and undergo the light-induced excited Spin state trapping (LIESST) effect at low temperatures. For each compound, the thermal Spin Transition temperature, T1/2, and the relaxation temperature of the photo-induced high-Spin state, T(LIESST), have been systematically determined. It appears that T1/2 decreases with the metal dilution while T(LIESST) remains unchanged. This behaviour is discussed on the basis of the kinetic study governing the photo-induced back conversion.
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structural magnetic and photomagnetic studies of a mononuclear iron ii derivative exhibiting an exceptionally abrupt Spin Transition light induced thermal hysteresis phenomenon
Inorganic Chemistry, 1998Co-Authors: Jean-françois Létard, Daniel Chasseau, Philippe Guionneau, Judith A. K. Howard, Andrés E. Goeta, Louis Rabardel, Olivier KahnAbstract:The new Spin-crossover compound Fe(PM-BiA)2(NCS)2 with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of χMT (χM = molar magnetic susceptibility and T = temperature) has revealed an exceptionally abrupt Transition between low-Spin (LS) (S = 0) and high-Spin (HS) (S = 2) states with a well-reproducible hysteresis loop of 5 K (T1/2↓ = 168 K and T1/2↑ = 173 K). The crystal structure has been determined both at 298 K in the HS state and at 140 K in the LS state. The Spin Transition takes place without change of crystallographic space group (Pccn with Z = 4). The determination of the intermolecular contacts in the LS and HS forms has revealed a two-dimensional structural character. The enthalpy and entropy variations, ΔH and ΔS, associated with the Spin Transition have been deduced from heat capacity measurements. ΔS (= 58 J K-1 mol-1) is larger than for other Spin Transition bis(thiocyanato) iron(II) derivatives. At 10 K the well-known LIESST (light-induced excit...
Kamel Boukheddaden - One of the best experts on this subject based on the ideXlab platform.
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Spatio-temporal Investigations of the Incomplete Spin Transition in a Single Crystal of [Fe(2-pytrz)2{Pt(CN)4}]·3H2O: Experiment and Theory
Crystals, 2019Co-Authors: Houcem Fourati, Smail Triki, Guillaume Bouchez, Miguel Paez-espejo, Kamel BoukheddadenAbstract:Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the Spin-crossover single crystal [Fe(2-pytrz) 2 {Pt(CN) 4 }]·3H 2 O, which exhibits a first-order Spin Transition from a full high-Spin (HS) state at high temperature to an intermediate, high-Spin low-Spin (HS-LS) state, below 153 K, where only one of the two crystallographic Fe(II) centers switches from the HS to HS-LS state. In comparison with crystals undergoing a complete Spin Transition, the present transformation involves smaller volume changes at the Transition, which helps to preserving the crystal’s integrity. By analyzing the spatio-temporal properties of this Spin Transition, we evidenced a direct correlation between the orientation and shape of HS/HS-LS domain wall with the crystal’s shape. Thanks to the small volume change accompanying this Spin Transition, the analysis of the experimental data by an anisotropic reaction-diffusion model becomes very relevant and leads to an excellent agreement with the experimental observations.
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Interplay between a crystal's shape and spatiotemporal dynamics in a Spin Transition material
Physical Chemistry Chemical Physics, 2018Co-Authors: Houcem Fourati, Eric Milin, Ahmed Slimani, Guillaume Chastanet, Younes Abid, Smail Triki, Kamel BoukheddadenAbstract:We investigated by means of optical microscopy (OM) the spatiotemporal features of the thermo-induced Spin Transition of [Fe(2-pytrz)2{Pd(CN)4}]·3H2O (1) (2-pytrz = 4-(2-pyridyl)-1,2,4,4H-triazole) single crystals having two different shapes (triangle and rectangle). While magnetic and calorimetric measurements, performed on a polycrystalline material, showed the respective average heating and cooling Transition temperatures of (Tdown1/2 ∼ 152 K, Tup1/2 ∼ 154 K) and (Tdown1/2 ∼ 160.0 K, Tup1/2 ∼ 163.5 K), OM studies performed on a unique single crystal revealed significantly different switching temperatures (Tdown1/2 ∼ 152 K and Tup1/2 ∼ 162 K). OM investigations showed an interface spreading over all crystals during the Spin Transition. Thanks to the color contrast between the low-Spin (LS) and the high-Spin (HS) states, we have been able to follow the real time dynamics of the Spin Transition between these two Spin states, as well as access the thermal hysteresis loop of each single crystal. After image processing, the HS–LS interface's velocity was carefully estimated in the ranges [4.4–8.5] μm s−1 and [2.5–5.5] μm s−1 on cooling and heating, respectively. In addition, we found that the velocity of the interface is shape-dependent, and accelerates nearby the crystal's borders. Interestingly, we observed that during the propagation process, the interface optimizes its shape so as to minimize the excess of elastic energy arising from the lattice parameter misfit between the LS and HS phases. All of these original experimental results are well reproduced using a spatiotemporal model based on the description of the Spin-crossover problem as a reaction diffusion phenomenon.
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Unprecedented trinuclear FeII triazole-based complex exhibiting a concerted and complete sharp Spin Transition above room temperature
Chemical Communications, 2017Co-Authors: Narsimhulu Pittala, Kamel Boukheddaden, Guillaume Chastanet, Smail Triki, Franck Thétiot, Catherine Charles, Mathieu MarchivieAbstract:We report an original triazole-based trinuclear FeII complex [Fe3(bntrz)6(tcnset)6] (1) (bntrz = 4-(benzyl)-1,2,4-triazole, tcnset- = 1,1,3,3-tetracyano-2-thioethylpropenide anion) as the first related example to date that displays a complete Spin Transition involving the three Fe(II) metal centers. Magnetic and heat capacity measurements, and variable temperature X-ray diffraction revealed a one-step first-order [HS-HS-HS]/[LS-LS-LS] Transition above room temperature (T1/2 = 318 K) despite the presence of two chemically different metal centers in the trimer (Fe2-Fe1-Fe2). The strong ferro-elastic interactions, between the three metal centers, have been identified as the source of the concerted Spin Transition in this trinuclear complex
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Neutral ferric complexes of salicylaldehyde thiosemicarbazone ligands: An exceptional family of complexes exhibiting discontinuous Spin Transition behavior
Polyhedron, 2014Co-Authors: Sébastien Floquet, Kamel Boukheddaden, Eric Rivière, Denis Morineau, Marie-laure BoillotAbstract:Three neutral thiosemicarbazone ferric complexes of general formulas [Fe(H5XThsa)(5XThsa)]*H2O have been prepared and studied by magnetic susceptibility, DSC and Mössbauer measurements. The three compounds exhibit an abrupt Spin Transition associated with thermal hysteresis, a still rarely observed behavior for ferric complexes. DSC and Mössbauer measurements allowed confirming that these Spin Transition processes are coupled with a first order crystallographic phase Transition whose thermodynamical parameters have been determined. Finally, it can be highlighted from the comparison of properties observed for these compounds with the literature that the synthetic procedures are a crucial point for the magnetic properties.
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Dynamic triggering of a Spin-Transition by a pulsed magnetic field
European Physical Journal B, 2000Co-Authors: Azzedine Bousseksou, N. Negre, M. Goiran, Lionel Salmon, Jean-pierre Tuchagues, Marie-laure Boillot, Kamel Boukheddaden, François VarretAbstract:We report the first study of the effect of a high pulsed magnetic field on a Spin Transition complex in the solid state. The high Spin fraction was determined by optical reflectivity. Sizeable effects are observed for the well-known Spin Transition solid Fe(Phen)2(NCS)2. In the hysteresis loop temperature range, an increase in the HS fraction is obtained, with an irreversible (reversible) character in the ascending (descending) branch of the loop. The time dependence of the HS fraction provides information on the kinetics of the Spin-crossover process at the Spin Transition.
Olivier Kahn - One of the best experts on this subject based on the ideXlab platform.
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structural magnetic and photomagnetic studies of a mononuclear iron ii derivative exhibiting an exceptionally abrupt Spin Transition light induced thermal hysteresis phenomenon
Inorganic Chemistry, 1998Co-Authors: Jean-françois Létard, Daniel Chasseau, Philippe Guionneau, Judith A. K. Howard, Andrés E. Goeta, Louis Rabardel, Olivier KahnAbstract:The new Spin-crossover compound Fe(PM-BiA)2(NCS)2 with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of χMT (χM = molar magnetic susceptibility and T = temperature) has revealed an exceptionally abrupt Transition between low-Spin (LS) (S = 0) and high-Spin (HS) (S = 2) states with a well-reproducible hysteresis loop of 5 K (T1/2↓ = 168 K and T1/2↑ = 173 K). The crystal structure has been determined both at 298 K in the HS state and at 140 K in the LS state. The Spin Transition takes place without change of crystallographic space group (Pccn with Z = 4). The determination of the intermolecular contacts in the LS and HS forms has revealed a two-dimensional structural character. The enthalpy and entropy variations, ΔH and ΔS, associated with the Spin Transition have been deduced from heat capacity measurements. ΔS (= 58 J K-1 mol-1) is larger than for other Spin Transition bis(thiocyanato) iron(II) derivatives. At 10 K the well-known LIESST (light-induced excit...
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Spin Transition Molecular Alloys: An Attempt of Fine Tuning of the Transition Temperatures
Chemistry of Materials, 1997Co-Authors: Olivier Kahn, Line Sommier, Epiphane CodjoviAbstract:The goal of this work has been to propose a novel approach to fine tune the Transition temperatures of Spin Transition materials, based on the concept of Spin Transition molecular alloys. It has concerned the alloys of composition [Fe(R1trz)3-3x(R2trz)3x]A2, where R1trz and R2trz stand for two different 4-substituted-1,2,4-triazole ligands, and A- stands for a counteranion. It has been shown that for any composition defined by x the alloy gives a unique Spin Transition regime, while the mixture (1 − x)[Fe(R1trz)3]A2 + x[Fe(R2trz)3]A2 of the same chemical composition shows two Spin Transition regimes with the relative intensities 1 − x and x, respectively. In the case of the alloys [Fe(Htrz)3-3x(NH2trz)3x](ClO4)2·H2O, the inversion temperatures T1/2↑ and T1/2↓ in the warming and cooling modes, respectively, have been found to vary almost linearly as a function of x. For x = 0.15, the alloy is bistable at room temperature. A theoretical treatment of this molecular alloy effect in the mean-field approximatio...
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Iron(II)-1,2,4-Triazole Spin Transition Molecular Materials
Philosophical Transactions of the Royal Society of London. Series A: Mathematical Physical and Engineering Sciences, 1996Co-Authors: Olivier Kahn, Epiphane CodjoviAbstract:The phenomenon of Spin Transition is probably one of the most spectacular examples of molecular bistability. Our main goal along this line concerns the design of molecular materials exhibiting abrupt Spin Transitions accompanied by thermochromic and large thermal hysteresis effects. The ideal situation, in terms of possible application of these compounds as active elements of memory devices, is realized when room temperature falls in the middle of the thermal hysteresis loop. In this context, we review our work concerning iron(II)-1,2,4-triazole compounds. We first introduce the idea that the cooperativity should be more pronounced in polymeric than in mononuclear compounds. Then we present some results concerning trinuclear iron(II)-1,2,4-triazole species. The heart of the paper is devoted to the polymeric compounds of formulae \[Fe(Htrz)$\_{2}$(trz)\](BF$\_{4}$) and \[Fe(Htrz)$\_{3}$\](BF$\_{4}$)$\_{2}\cdot $ H$\_{2}$O. We report first on the magnetic, optical and calorimetric, then on the structural properties of these compounds. Afterwards, we introduce the concept of Spin Transition molecular alloy, and emphasize that it is possible to fine tune the Spin Transition regime of these alloys through their chemical composition. For some alloys, room temperature falls within the thermal hysteresis loop. In the conclusion, the mechanism of cooperativity in the Spin Transition polymeric compounds is briefly discussed.
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Cooperativity and Anticooperativity in Spin Transition Compounds; Macroscopic Approach and Orbital Modelization
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1993Co-Authors: Hélène Bolvin, Olivier KahnAbstract:The intermolecular interaction parameter occuring in the thermodynamical approach of Spin Transition proposed by Slichter and Drickamer is analyzed at the microscopic level. Then, an orbital model is proposed, to estimate this microscopic interaction between two neighbouring Spin Transition molecules. It shows that there is a competition between the direct interaction between the two metal centers and the indirect interaction through the ligands
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From Spin Transition to display and memory devices
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1993Co-Authors: Charlotte Jay, Olivier Kahn, Françoise Groliere, J. KröberAbstract:Abstract After a presentation of a user-friendly and reliable optical technique to characterize the Spin Transition phenomenon in iron II derivatives, this paper describes the first realization of a thermally addressed display. This new technology, still at the beginning of its development, is promising for further recording or display applications.
