Phonon coupled cooperative low-spin 1A1high-spin 5T2 transition in [Fe(phen)2(NCS)2] and [Fe(phen)2(NCSe)2] crystals

Sorai, Michio; Seki, Syûzô

doi:10.1016/s0022-3697(74)80010-7

Cited by 486 publications

(387 citation statements)

References 33 publications

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“…The energy loss arising at the boundary surface between the two phases may be quite small and the energy gain due to mixing entropy would compensate for it, giving rise to the coexistence of the two phases. This phenomenon might correspond to the model proposed by Frenkel (1947) and Sorai & Seki (1974). The twinning observed in the low-temperature modification is suggestive of a small energy loss.…”

Section: Structural Change With the Transitionsupporting

confidence: 87%

The crystal structure of sodium 7,7,8,8-tetracyanoquinodimethanide at 80°C

Konno¹,

Saitō²

1975

Acta Crystallogr Sect B

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The crystal structure of the high-temperature modification of Na+TCNQ -has been determined by X-ray diffraction at 80°C. The crystals are monoclinic with space group P21/n and lattice constants: a=3.512 (1), b=11.866 (2), e=12.465 (3) A, p=98.21 (2) ° and Z=2. Weak reflexions with h and k both odd in the low-temperature phase disappeared completely at about 73 °C. The intensity variations of two selected reflexions with temperature indicated that the transition is essentially first-order and the low-and high-temperature phases coexist in the range 59 to 73 °C. The structure was refined by the full-matrix least-squares method to an R of 0.033 for the 675 observed reflexions collected by diffractometry. TCNQ-ions are stacked face-to-face to form columns along the a axis with an equal interplanar spacing of 3.385 A above the transition temperature, whereas in the low-temperature phase they are arranged with alternate spacings of 3.21 and 3-49 A, and TCNQ dimers are present.

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Section: Structural Change With the Transitionsupporting

confidence: 87%

The crystal structure of sodium 7,7,8,8-tetracyanoquinodimethanide at 80°C

Konno¹,

Saitō²

1975

Acta Crystallogr Sect B

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“…The overall variations DH = 8.4 kJ mol À1 and DS = 53 J K À1 mol À1 are within the experimental range generally observed for iron(ii) SCO compounds. [30] It is worth noting that a symmetric distribution of DS between the two steps should be expected. However, DS 1 is significantly smaller than DS 2 .…”

Section: Differential Scanning Calorimetry (Dsc) Measurementsmentioning

confidence: 99%

Thermal‐ and Photoinduced Spin‐State Switching in an Unprecedented Three‐Dimensional Bimetallic Coordination Polymer

Niel

Thompson

Goeta

et al. 2005

Chemistry A European J

129

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The compound {Fe(pmd)[Ag(CN)2][Ag2(CN)3]} (pmd=pyrimidine) was synthesized and characterized. Magnetic, calorimetric and single crystal visible spectroscopic studies demonstrate the occurrence of a two-step high-spin (HS) low-spin (LS) transition. The critical temperatures are Tc1=185 and Tc2=148 K. Each step involves 50 % of the iron centers, with the low-temperature step showing a hysteresis of 2.5 K. The enthalpy and entropy variations associated with the two steps are H1=3.6±0.4 kJ mol-1 and S1=19.5±3 J K-1 mol-1; H2=4.8±0.4 kJ mol-1 and S2=33.5±3 J K-1 mol-1. Photomagnetic and visible spectroscopy experiments show that below 50 K, where the LS state is the thermodynamically stable state, the compound can be switched quantitatively to the HS state using green-red light (550-650 nm). HS-to-LS relaxation experiments in the dark at temperatures between 15 and 55 K show that the relaxation takes place via a two-step cooperative process, which was analyzed in the context of the mean field theory. The crystal structure has been studied at 290, 220, 170, 90 and 30 K together with 30 K after irradiation. The compound adopts monoclinic symmetry (P21/c, Z=16) at all temperatures. There are five [FeN6] pseudo-octahedral sites linked by pmd, [Ag(CN)2]- and [Ag2(CN)3]- bridging ligands to form an unprecedented three-dimensional (6,6) topology. The structural analysis allows for an understanding of the microscopic mechanism of the two-step behavior of the thermally induced spin transition as well as the corresponding relaxation of the photoexcited compound based on the individual changes of the five sites. Synergy between metallophilic interactions and the spin transition is also shown by the variation of the AgAg distances. Correlations between the variation of the unit-cell volume and the change of AgAg interactions within each step with the asymmetric change of the anomalous heat capacity have also been inferred

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“…This results in a drastic change in the density of vibrational states, mainly in the metal-ligand skeletal vibrational modes. This leads, of course, to significantly higher vibrational entropy in the HS state [31]. The entropy change accompanying the SC can be represented as the sum of electronic, configurational and motional, i.e.…”

Section: Hs Lsmentioning

confidence: 99%

Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

Szilágyi¹,

Dorbes²,

Molnár³

et al. 2008

Journal of Physics and Chemistry of Solids

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A c c e p t e d m a n u s c r i p t

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Phonon coupled cooperative low-spin 1A1high-spin 5T2 transition in [Fe(phen)2(NCS)2] and [Fe(phen)2(NCSe)2] crystals

Cited by 486 publications

References 33 publications

The crystal structure of sodium 7,7,8,8-tetracyanoquinodimethanide at 80°C

The crystal structure of sodium 7,7,8,8-tetracyanoquinodimethanide at 80°C

Thermal‐ and Photoinduced Spin‐State Switching in an Unprecedented Three‐Dimensional Bimetallic Coordination Polymer

Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

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