Total free energy of a spin-crossover molecular system

Spiering, H.; Boukheddaden, Kamel; Linarès, Jorge; Varret, F.

doi:10.1103/physrevb.70.184106

Cited by 130 publications

(114 citation statements)

References 42 publications

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“…The vibrational contribution to the entropy, which can be derived from vibrational spectra and DFT calculations [30,[46][47][48] is not only the additional driving force of the spin transition. Additionally, low energy phonons contribute to the cooperativity as suggested by theoretical considerations based on the Ising model [49] and on elasticity theory [50]. As already stated, we have, by use of the DFT procedure described in [47], previously calculated the vibrational contribution to the entropy for the HLLLH to HLHLH and the HHLHH to HHHHH transitions of the systems described here [28].…”

Section: Hhhhllh Isomersmentioning

confidence: 84%

Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study

et al. 2016

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Abstract:The nuclear inelastic scattering signatures of the low-spin centers of the methanosulphonate, tosylate, and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole) 3 ] 2+ ) n have been compared for the low-spin phase, for the mixed high-spin and low-spin phases, as well as for Zn(II) diluted samples. Within this series a change in the vibrational pattern in the 320-500 cm´1 region is observed. Significant shifts and decreasing intensity of bands at~320 cm´1 and bands over 400 cm´1 are observed as the molar fraction of the low-spin (LS) centers decrease. Density functional theory calculations using Gaussian09 (B3LYP/CEP-31G) for pentameric, heptameric, and nonameric model molecules yielded the normal modes of several spin isomers: these include the all high-spin (HS) and the all low-spin (LS) configuration but also mixtures of LS and HS centers, with a special focus on those with LS centers in a HS matrix and vice versa. The calculations reproduce the observed spectral changes and show that they are caused by strain extorted on a LS Fe(II) center by its HS neighbors due to the rigid character of the bridging aminotriazole ligand. Additionally, the normal mode analysis of several spin isomers points towards a coupling of the vibrations of the iron centers of the same spin: the metal-ligand stretching modes of the all LS and the all HS spin isomers reveal a collective character: all centers of the same spin are involved in characteristic normal modes. For the isomers containing both LS and HS centers, the vibrational behavior corresponds to two different subsets (sublattices) the vibrational modes of which are not coupled. Finally, the calculation of nuclear inelastic scattering data of spin isomers containing a ca. 1:1 mixture of HS and LS Fe(II) points towards the formation of blocks of the same spin during the spin transition, rather than to alternate structures with a HS-LS-HS-LS-HS motif.

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Section: Hhhhllh Isomersmentioning

confidence: 84%

Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study

et al. 2016

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“…Another approach-the so-called elasticity theory-was proposed by Spiering et al for modeling of various SCO behaviors-including stepped transition curves. 44,56 Monte Carlo techniques have been also implemented with good fit to the experimental two-step n HS (T) curves in the isobaric regime. 57 These authors were also the first to predict the establishment of a "chessboard structure" in the IP.…”

Section: Discussionmentioning

confidence: 99%

Pressure-induced two-step spin transition with structural symmetry breaking: X-ray diffraction, magnetic, and Raman studies

et al. 2011

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We have used single-crystal x-ray diffraction, Raman spectroscopy, and magnetometry to investigate the effect of hydrostatic pressures up to 16 kbar on the molecular spin crossover complex [Fe II (bapbpy)(NCS) 2 ]. A stepped first-order transition from the high-spin (HS) to low-spin (LS) phase was observed upon compression of single-crystal samples. The intermediate phase (IP) is stable between 4 and 11 kbar at room temperature. This phase is characterized by supercell reflections and tripling of the c-axis of the unit cell (C2/c) due to the formation of a periodic [HS-LS-LS] structural motif, as seen in the thermal stepped transition. The pressure-temperature phase diagram reveals an anomalous increase of the thermal hysteresis widths with increasing pressure and the stabilization of the IP across the investigated P-T space.

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“…In fact, many properties (mechanical, thermal, structural, morphological) might have an impact on the observed features. Mechanical (elastic) properties have to be considered because large elastic modulus (stiffness) is known to be an essential ingredient for cooperativity [35]. Information about lattice stiffness of (1) could be extracted through the measurement of the Debye temperature ( D = 198 K in the LS state [29]) from Mössbauer data [36].…”

Section: µMmentioning

confidence: 99%

Spatiotemporal dynamics of the spin transition in[Fe(HB(tz)3)2]single crystals

et al. 2017

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Azzedine (2017) Spatiotemporal dynamics of the spin transition in [Fe(HB(tz) ABSTRACTThe spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex [Fe(HB(tz)3)2] (tz = 1,2,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of ca. 1 K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic lowspin/high-spin phase boundaries up to 500 µm/s and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin high-spin transition induced by a local photothermal excitation generated by a spatially localized (Ø = 2 µm) continuous laser beam. Interesting phenomena have been evidenced both in quasi-static and dynamic conditions (threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, thermal cut-off frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics and allowed an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model. 2

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Total free energy of a spin-crossover molecular system

Cited by 130 publications

References 42 publications

Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study

Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study

Pressure-induced two-step spin transition with structural symmetry breaking: X-ray diffraction, magnetic, and Raman studies

Spatiotemporal dynamics of the spin transition in[Fe(HB(tz)3)2]single crystals

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