Heat capacity and dual spin-transitions in the crossover system [Fe(2-pic)3]Cl2·EtOH

Calorimetric investigations of phase transitions in which electrons are directly involved

“…The observation of double peaks accords with the reinvestigation of Mössbauer spectroscopy and magnetic susceptibility measurements by Gütlich and his collaborators, (45) showing that a two-step spin conversion in the crossover region occurs at T = 114.0 K and T = 120.7 K. Sasaki and Kambara (46) suggested a theoretical model for the two-step spin crossover assuming a sublattice structure for the HS and LS complexes, between which a quasi "antiferromagnetic" interaction is assumed. Real et al (47) also supported the short-range (44) antiferromagnetic interactions as the source of step-like spin crossover. Recent interpretation by Spiering et al (48,49) is based on a short-range interaction which is present in addition to the long-range elastic interaction between the spin-changing molecules.…”

“…In order to elucidate the spin crossover behaviour of these complexes from energetic and entropic viewpoints, we measured their heat capacities by adiabatic calorimetry. Figure 7 shows temperature dependence of the molar heat capacity (44) of [Fe(2-pic) 3 ]Cl 2 · C 2 H 5 OH. This complex exhibited two heat capacity peaks due to phase transitions at T = 114.04 K and T = 122.21 K. As the peak temperatures agree with the spin transition temperature estimated from the Mössbauer spectroscopy, these two peaks are closely related to the spin crossover event.…”

Interplay of Spin Conversion and Structural Phase Transformations: Re‐Entrant Phase Transitions in the 2‐Propanol Solvate of Tris(2‐picolylamine)iron(II) Dichloride

“…[23,24] It was suggested that solvent disorder in the [Fe II (2-pic) 3 ]Cl 2 ethanol solvate modifies the elastic properties and therefore affects spin conversion. [25] We note that the role of the solvent molecules is more complex, at least in the series of [Fe II (2-pic) 3 ]Cl 2 solvates.…”

Photoinduced spin crossover in a Fe-picolylamine complex: A far-infrared study on single crystals

“…Consequently, the phonon density of states is modified, leading to the large ∆S ph . 18,19 Since the photoinduced crossover is observed at much lower temperatures, high-frequency phonons are quenched, and phonons with much lower frequencies may play important roles in terms of the entropy in PIHS. It is interesting that, in Fig.…”

“…18 For the thermal crossover in Fe-pic, the phonon part (∆S ph ) of the observed entropy change is as large as 56 %. 19 This acts as a strong driving force for the crossover and also increases the cooperativity. 3, 20 The large ∆S ph results from the strong anharmonicity of the FeN 6 vibrations: When the average lattice constants change upon the crossover, the phonon frequencies also change due to the anharmonicity.…”