Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

Sorai, Michio; Nakano, Motohiro; Miyazaki, Yuji

doi:10.1021/cr960049g

Cited by 161 publications

(84 citation statements)

References 452 publications

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“…5(a). The d value obtained from the low temperature fit is very close to the T 3 dependence expected for 3D AFM spin waves 60,61 . Hence, it is likely that 1 goes through a transition to LRO within the experimental temperature range.…”

Section: A Crystal Structuressupporting

confidence: 78%

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

et al. 2016

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Magnetism in a family of S = 1 square lattice antiferromagnets NiX 2 (pyz) 2 (X = Cl, Br, I, NCS; pyz = pyrazine) The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3) and NCS (4)) were determined at 298 K by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]ZF6 (Z = P, Sb) which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggering of adjacent layers. Long-range antiferromagnetic order occurs below 1.5 (Cl), 1.9 (Br and NCS) and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3 and 4 are measured by electron spin resonance where no zero-field splitting was found. The magnetism of 1-4 crosses a spectrum from quasi-two-dimensional to three-dimensional antiferromagnetism. An excellent agreement was found between the pulsedfield magnetization, magnetic susceptibility and TN of 2 and 4. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. 3 is characterized as a three-dimensional antiferromagnet with the interlayer interaction (J ⊥ ) slightly stronger than the interaction within the two-dimensional [Ni(pyz)2] 2+ square planes (Jpyz).

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Section: A Crystal Structuressupporting

confidence: 78%

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

et al. 2016

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“…Reversible transition between low-spin (LS, 1 A 1 ) and high-spin (HS, 5 T 2 ) states, triggered by temperature, pressure, magnetic field, or light, is a well-established phenomenon, which has been observed mainly in pseudo-octahedral iron(II) compounds. [1][2][3][4][5][6][7][8][9] It induces a change in the metal-ligand distances, which for N-ligands are, on average, 0.16 shorter in the LS than in the HS state. The ability of the crystal lattice to efficiently transmit the changes in the coordination sphere geometry from one metal site to another is what defines the steepness of the spin transition.…”

Section: Introductionmentioning

confidence: 99%

First Dicyanamide‐Bridged Spin‐Crossover Coordination Polymer: Synthesis, Structural, Magnetic, and Spectroscopic Studies

Genre

Jeanneau

Bousseksou

et al. 2007

Chemistry A European J

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We report here on the synthesis and characterisation of a first iron(II) spin-crossover coordination polymer with the dca spacer ligand, having the formula [Fe(aqin)2(dca)]ClO4.MeOH (aqin=8-aminoquinoline, dca=dicyanamide), which displays a two-step complete spin transition. Variable-temperature magnetic susceptibility measurements and Mössbauer spectroscopy have revealed that the two relatively gradual steps are centred at 215 and 186 K and are separated by an inflection point at about 201 K, at which 50 % of the complex molecules undergo a spin transition. The two steps are related to the existence of two crystallographically inequivalent metal sites, as confirmed by the structural and Mössbauer studies. The crystal structure was resolved at 293 K (HS form) and 130 K (LS form). Both spin-state structures belong to the triclinic P1 space group (Z=2). The complex assumes a linear chain structure, in which the active iron(II) sites are linked to each other by anionic dicyanamide ligands acting as chemical bridges. The Fe-Fe distances through the dca ligand are 8.119(1) and 7.835(1) A in the high-spin and low-spin structures, respectively. The polymeric chains extend along a (1, 0, -1) axis and are packed in sheets, between which the perchlorate anions and methanol molecules are inserted. The complex molecules are linked together by pi-stacking interactions and H-bonding between the H-donor aqin ligands and the perchlorate ions. These structural features provide a basis for cooperative interactions in the crystal lattice. Analysis of the two-step spin-crossover character in this compound suggests that covalent interactions through the spacer ligand do not provide the main mechanism of cooperativity.

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“…All features presented here are also expected in other switchable molecular solids, such as Prussian Blue Analogs, Valence tautomers, Jahn-Teller switches, charge-transfer salts, which are frequently reviewed (recent refs. [43][44][45][46][47]), because of their potential applications in optical data storage. * * * …”

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confidence: 99%

Light-induced phase separation in the [Fe(ptz)₆] (BF₄)₂spin-crossover single crystal

et al. 2007

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-We present novel insight on like-spin domains (LSD) in cooperative spin transition solids by following the photo-transformation and the subsequent relaxation of a [Fe(ptz)6](BF4)2 single crystal in the vicinity of the light-induced instability. Self-organization under light is observed, accompanied by Barkhausen-like noise and jumps which reveal the presence of elastic interactions between LSDs. The light-induced phase separation process is discussed in terms of a dynamic potential providing spinodal instability in the corresponding temperature range. This useful concept is applicable to all types of switchable molecular solids.

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Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

Cited by 161 publications

References 452 publications

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

First Dicyanamide‐Bridged Spin‐Crossover Coordination Polymer: Synthesis, Structural, Magnetic, and Spectroscopic Studies

Light-induced phase separation in the [Fe(ptz)₆] (BF₄)₂spin-crossover single crystal

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Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

Cited by 161 publications

References 452 publications

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine)

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine)

First Dicyanamide‐Bridged Spin‐Crossover Coordination Polymer: Synthesis, Structural, Magnetic, and Spectroscopic Studies

Light-induced phase separation in the [Fe(ptz)6] (BF4)2spin-crossover single crystal

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Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

Light-induced phase separation in the [Fe(ptz)₆] (BF₄)₂spin-crossover single crystal