Polymorphism-Dependent Spin-Crossover: Hysteretic Two-Step Spin Transition with an Ordered [HS–HS–LS] Intermediate Phase

Luan, Jie; Zhou, Jian; Li, Zhan; Zhu, Bowen; Wang, Huisi; Bao, Xin; Liu, Wei; Tong, Ming‐Liang; Peng, Guo; Peng, Haonan; Salmon, Lionel; Bousseksou, Azzedine

doi:10.1021/acs.inorgchem.5b00629

Cited by 52 publications

(45 citation statements)

References 34 publications

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“…The crystal structure was determined at 123 K (crystallographic data and refinement parameters are listed in Tables S1 and S2, Supporting Information). Complex 1 crystallizes in the monoclinic C 2/ c space group and its molecular structure (Figure ) is comparable to those of reported analogues based on related tetradentate ligands . The asymmetric unit contains half of a complex centered on a twofold axis.…”

Section: Figuresupporting

confidence: 62%

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear Fe^II Complex

Chen

Cai

et al. 2019

Angewandte Chemie

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A mononuclear FeII complex that shows a high‐spin (S=2) paramagnetic behavior at all temperatures (with standard temperature‐scan rates, ≈1 K min−1) has, in fact, a low‐spin (S=0) ground state below 100 K. This low‐spin state is not easily accessible due to the extremely slow dynamics of the spin‐crossover process—a full relaxation from the metastable high‐spin state to the low‐spin ground state takes more than 5 h below 80 K. Bidirectional photo‐switching of the FeII state is achieved reproducibly by two selective irradiations (at 530–590 and 830–850 nm). The slow dynamics of the spin‐crossover and the strong structural cooperativity result in a remarkably wide 95‐K hysteresis loop induced by both temperature and selected light stimuli.

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Section: Figuresupporting

confidence: 62%

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear Fe^II Complex

Chen

Cai

et al. 2019

Angewandte Chemie

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“…At 100 K (IP state) the unit cell triples displaying a HS-HS-LS pattern. However, the order in this IP = 2HS-1LS is produced in a different way to that described in the previous example, namely a layer constituted of Fe2(LS) sites is separated by two consecutive identical layers made up of Fe1(HS) sites (Figure 3) [35]. 3 •K•mol −1 ), characterized by a hysteresis loop 10 K wide centered at Tc1 = 101 K, involves the remaining 2/3 of the HS species.…”

Section: Introductionmentioning

confidence: 93%

“…At 100 K (IP state) the unit cell triples displaying a HS-HS-LS pattern. However, the order in this IP = 2HS-1LS is produced in a different way to that described in the previous example, namely a layer constituted of Fe2(LS) sites is separated by two consecutive identical layers made up of Fe1(HS) sites ( Figure 3) [35]. The multicomponent mononuclear complex [Fe II (dpp)2][Ni(mnt)2]2•MeNO2, (dpp = 2,6-bis(pyrazol-1-yl)pyridine (see Appendix Figure A1) and mnt = maleonitriledithiolate) displays a complicated SCO behavior.…”

Section: Introductionmentioning

confidence: 93%

Symmetry Breaking in Iron(II) Spin-Crossover Molecular Crystals

2016

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Abstract:This review provides an up to date survey of a singular class of iron(II) spin crossover (SCO) molecular materials that undergo high-spin (HS) Ø low-spin (LS) phase transitions accompanied by crystallographic symmetry breaking (CSB). Particular interest has been focused on a variety of complexes that exhibit one-step or stepwise SCO behavior and CSB. Most of them afford excellent examples of well-ordered 1HS-1LS, 2HS-1LS or 1HS-2LS intermediate phases (IP) and represent an important platform to disclose microscopic mechanisms responsible for cooperativity and ordering in such multistable materials.

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“…However, even if there is a unique SCO center in the crystal, inequivalence between SCO centers may spontaneously originate as a consequence of crystallographic symmetry breaking. Although, crystallographic symmetry breaking giving intermediate steps was previously observed for the mononuclear SCO complexes [Fe 27-29 So far, a relatively small number of complete two-step or incomplete (only one step of two expected) SCO events with symmetry breaking have been observed in mononuclear, [30][31][32][33][34][35][36][37][38][39] polynuclear, [40][41][42][43] and polymeric [44][45][46][47][48][49][50][51][52][53] Fe II SCO complexes, and reviewed recently. 54,55 This phenomenology has also been described for a reduced number of Fe III , [56][57][58][59][60] Co II 61 and Mn III 62 complexes.…”

Section: Introductionmentioning

confidence: 99%

Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer

Trzop

Valverde‐Muñoz

Piñeiro‐López

et al. 2017

Crystal Growth & Design

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Competition between spin-crossover (SCO) and structural ligand ordering is identified as responsible for multi-stability and generation of six different phases in a rigid two-dimensional (2D) coordination polymer formulated {Fe Furthermore, two additional phases are generated at low temperature. One, LS2 (HS = 0, phase 5), is due to spontaneous symmetry breaking of the LS1 state below 85 K. The other, results from irradiating the low-temperature LS2 phase at 15 K with red light to photo-generate a HS phase of low symmetry (HS*) (HS = 1, phase 6). Detailed structural studies of the six phases unravel the pivotal role played by the internal dihedral angle of the 4,4'-bipy ligands in the microscopic mechanism responsible for multistability and multi-step behavior in 1.Competing phases involving spin-state and ligand structural orderings in a multistable two-dimensional spin crossover coordination polymer INTRODUCTIONIron(II) spin crossover (SCO) complexes are switchable molecular materials that respond to environmental stimuli (T, P, light, analytes) through changes in magnetic, optical, electrical and mechanical properties associated with the high-(HS) and low-spin (LS) states of the SCO centre. The intrinsic on-off nature of the LSHS switch has attracted much interest not only because it constitutes an excellent platform for investigating models of thermal-, pressure and photoinduced phase transitions 1-13 in molecular materials but also because many expectancies have been created regarding to the conception of SCO-based devices, i.e. sensors, actuators and memories. [14][15][16][17][18][19][20][21][22][23][24] This has led to an impressive growth of the SCO field in the last decade as a result of cross-seeding interaction between different areas of research ranging from coordination chemistry, materials science and solid state physics.A pivotal current aspect that transcends the SCO research is the understanding of the elusive principles underlying cooperativity in multi-step spin transitions in the solid-state.Steps may occur when elastic forces favor competition between spatial periodicities of structural inequivalent SCO centers. For example, the presence of crystallographically distinct sites with different ligand field strengths. However, even if there is a unique SCO center in the crystal, inequivalence between SCO centers may spontaneously originate as a consequence of crystallographic symmetry breaking. Although, crystallographic symmetry breaking giving intermediate steps was previously observed for the mononuclear SCO complexes [Fe

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Polymorphism-Dependent Spin-Crossover: Hysteretic Two-Step Spin Transition with an Ordered [HS–HS–LS] Intermediate Phase

Abstract: A mononuclear iron(II) complex has been isolated in two polymorphs. Polymorph 1b remains high-spin over all temperatures, whereas polymorph 1a undergoes a cooperative two-step spin crossover accompanied by symmetry breaking, showing an ordered 2:1 high-spin-low-spin intermediate phase.

Cited by 52 publications

References 34 publications

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear Fe^II Complex

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear Fe^II Complex

Symmetry Breaking in Iron(II) Spin-Crossover Molecular Crystals

Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer

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Polymorphism-Dependent Spin-Crossover: Hysteretic Two-Step Spin Transition with an Ordered [HS–HS–LS] Intermediate Phase

Abstract: A mononuclear iron(II) complex has been isolated in two polymorphs. Polymorph 1b remains high-spin over all temperatures, whereas polymorph 1a undergoes a cooperative two-step spin crossover accompanied by symmetry breaking, showing an ordered 2:1 high-spin-low-spin intermediate phase.

Cited by 52 publications

References 34 publications

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear FeII Complex

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear FeII Complex

Symmetry Breaking in Iron(II) Spin-Crossover Molecular Crystals

Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer

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Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear Fe^II Complex

Slow Dynamics of the Spin‐Crossover Process in an Apparent High‐Spin Mononuclear Fe^II Complex