Quasi-static nature of the light induced thermal hysteresis in [Fe(ptz)6](BF4)2 spin-transition solid

Jeftić, Jelena; Matsarski, Marie; Hauser, Andreas; Goujon, Antoine; Codjovi, Épiphane; Linarès, Jorge; Varret, F.

doi:10.1016/s0277-5387(01)00660-x

Cited by 19 publications

(7 citation statements)

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“…We interpreted this threshold behavior in terms of the dynamical phase transition 21 of the photoexcited steady state from the ͗n HS ͘Ϸ0 state ͑I ഛ 2 mW/mm 2 ͒ to the ͗n HS ͘Ϸ1͑I ജ 2 mW/mm 2 ͒ state. We further observed optical hysteresis 26 between the I-increasing run and the I-decreasing run, perhaps due to the significant structural change at the PIPT of ͓Fe͑ptz͒ 6 ͔͑BF 4 ͒ 2 . 25 Now, let us qualitatively analyze the experimentally obtained n HS -T curve ͑see ation process of the HS species.…”

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confidence: 67%

Cooperative formation of high-spin species in a photoexcited spin-crossover complex

et al. 2006

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The dynamics of the photoinduced phase transition was investigated in a prototypical spin crossover complex, ͓Fe͑ptz͒ 6 ͔͑BF 4 ͒ 2 ͑ptz= 1-propyltetrazole͒, under photoexcitation at 77 K near the transition temperature ͑T c = 130 K͒. When the excitation power I exceeds Ϸ1 mW/mm 2 , we observed an "acceleration" of the creation rate of the density n HS of the high-spin ͑HS͒ species after a characteristic incubation period. The "acceleration" is interpreted in terms of the negative pressure effect; the photocreated HS species with a larger ionic radius expands the volume to cause the structural phase transition.

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confidence: 67%

Cooperative formation of high-spin species in a photoexcited spin-crossover complex

et al. 2006

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“…The F M 's s may be directly deduced from the experimental flipping ratios if the crystal structure of the compound is known. 6 The sample rod of the 5C1 diffractometer has been modified to carry out photoexcitation experiments. The principle of the experimental setup is shown in Fig.…”

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“…The kinetics of the photoswitching is in good agreement with previous results obtained by Mössbauer spectroscopy and magnetization measurements. 2,6 The magnetization curves of the photoinduced state as a function of field, at 2 K, obtained by PND and SQUID experiments, are presented in Fig. 3.…”

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Photoinduced molecular switching studied by polarized neutron diffraction

et al. 2003

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The photo-induced magnetization density of the photoswitchable ͓Fe͑ptz͒ 6 ͔(BF 4 ) 2 (ptzϭ1-propyltetrazole) spin crossover compound is reported. The photoswitching process is observed by using a experimental setup allowing both light illumination and polarized neutron diffraction measurements ͑PND͒. We studied the photoexcitation kinetics, and the photoinduced magnetic properties of the ͓Fe͑ptz͒ 6 ͔(BF 4 ) 2 compound by PND, which evidenced a complete photoprocess. The temperature dependence of the photoinduced magnetization obtained by PND is well described by an Ising model taking into account the magnetic anisotropy and the spin-orbit coupling. The thermal relaxation towards the stable electronic state was observed in the 55-60-K temperature interval. The magnetization density around the Fe position is well described by the Fe 2ϩ magnetic form factor.

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“…The discontinuity observed in the thermal variation of δ(LS) is also associated with the occurrence of SCO. These significant variations are due to the fact that HS and LS molecules have different geometries, as evidenced by X-ray analysis, and these two crystallographic phases afford different lattice contributions. 9a, …”

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confidence: 99%

“…Such a magnetic behavior can be triggered by cooperative interactions between the active metal sites in the crystal, and two strategies have been developed: the polymeric approach, where metal centers are covalently linked by chemical bridges, and the supramolecular approach, using intermolecular interactions in the crystal (π−π stacking, hydrogen bonding). Moreover, few examples of first-order (hysteretic) SCO triggered by a structural phase transition have been reported …”

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Structural−Electronic Correlation in the First-Order Phase Transition of [FeH₂L^2-Me](ClO₄)₂ (H₂L^2-Me = Bis[((2-methylimidazol-4-yl)methylidene)-3- aminopropyl]ethylenediamine)

et al. 2006

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The synthesis and detailed study of the new mononuclear spin crossover complex [Fe(II)H2L(2-Me)](ClO4)2 (where H2L(2-Me) = bis[((2-methylimidazol-4-yl)methylidene)-3-aminopropyl]ethylenediamine) are reported. Variable-temperature magnetic susceptibility measurements show the occurrence of a steep spin crossover centered at 171.5 K with a hysteresis loop of ca. 5 K width (T(/2)(increasing) = 174 K and T(1/2)(decreasing) = 169 K, for increasing and decreasing temperatures, respectively). The crystal structure has been resolved for the high-spin (HS) and low-spin (LS) states at 200 and 123 K, respectively, revealing a crystallographic phase transition that occurs concomitantly to the spin crossover: at 200 K, the complex crystallizes in the monoclinic system, space group P2(1)/n, while the space group is P2(1) at 123 K. The mean Fe-N distances are shortened by 0.2 A, but the thermal spin crossover is accompanied by significant structural changes: the rearrangement of the central atom C12 of a six-membered chelate ring of [Fe(II)H2L(2-Me)]2+ to two positions (C12A and C12B) and, consequently, the lack of an inversion center at 123 K (P2(1) space group). Both HS and LS supramolecular structures involve all possible hydrogen bonds between imidazole and amine NH functions, and perchlorate anions; however, the HS supramolecular structure is a one-dimensional (1D) network, and the LS phase may better be described as a two-dimensional (2D) extended structure of A and B molecules. The structural phase transition of [FeH2L(2-Me)](ClO4)2 seems to trigger the steep and hysteretic spin crossover. Discontinuities in the temperature dependence of the Mössbauer parameters (isomer shift and quadrupole splitting) at the spin crossover temperature confirmed the occurrence of a structural phase transition. The experimental enthalpy and entropy variations were determined by differential scanning calorimetry (DSC) as 7.5 +/- 0.4 kJ/mol and 45 +/- 3 J K(-1) mol(-1), respectively. The regular solution theory was applied to the experimental data, yielding an interaction parameter of Gamma = 3.36 kJ/mol, which is larger than 2RT(1/2), which fulfills the condition for observing hysteresis.

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Quasi-static nature of the light induced thermal hysteresis in [Fe(ptz)6](BF4)2 spin-transition solid

Cited by 19 publications

References 15 publications

Cooperative formation of high-spin species in a photoexcited spin-crossover complex

Cooperative formation of high-spin species in a photoexcited spin-crossover complex

Photoinduced molecular switching studied by polarized neutron diffraction

Structural−Electronic Correlation in the First-Order Phase Transition of [FeH₂L^2-Me](ClO₄)₂ (H₂L^2-Me = Bis[((2-methylimidazol-4-yl)methylidene)-3- aminopropyl]ethylenediamine)

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Quasi-static nature of the light induced thermal hysteresis in [Fe(ptz)6](BF4)2 spin-transition solid

Cited by 19 publications

References 15 publications

Cooperative formation of high-spin species in a photoexcited spin-crossover complex

Cooperative formation of high-spin species in a photoexcited spin-crossover complex

Photoinduced molecular switching studied by polarized neutron diffraction

Structural−Electronic Correlation in the First-Order Phase Transition of [FeH2L2-Me](ClO4)2 (H2L2-Me = Bis[((2-methylimidazol-4-yl)methylidene)-3- aminopropyl]ethylenediamine)

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Structural−Electronic Correlation in the First-Order Phase Transition of [FeH₂L^2-Me](ClO₄)₂ (H₂L^2-Me = Bis[((2-methylimidazol-4-yl)methylidene)-3- aminopropyl]ethylenediamine)