Special Issue "Spin Crossover (SCO) Research"

A special issue of Magnetochemistry (ISSN 2312-7481).

Deadline for manuscript submissions: closed (15 January 2016).

Special Issue Editors

Dr. Guillem Aromí
E-Mail Website
Guest Editor
Grup de Magnetisme i Molècules Funcionals (GMMF), Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
Fax: +34 93 490 7725
Interests: functional molecular materials, molecular magnetism, molecular based quantum computing, spin cross-over, spin transition, lanthanide coordination chemistry, transition metal coordination chemistry, supramolecular chemistry, ligand design
Prof. José Antonio Real
E-Mail Website
Guest Editor
Switchable Molecular Materials (SMolMat) group, Molecular Science Institute (ICMol), University of València, Catedràtic José Beltrán Martínez, 2, 46980 Paterna (València), Spain
Interests: molecular magnetism; spin crossover phenomena; coordination polymers; metallosupramolecular chemistry; multiproperty materials; functional materials

Special Issue Information

Dear Colleagues,

The awareness on the phenomenon of spin crossover dates back to almost a century ago, however, it still attracts increasing attention by researchers from various disciplines. Thus, the desire to better explain its fundamentals and exploit its potential as a molecular switching property illuminates new contributions by synthetic chemists, theoreticians, physicists, spectroscopists or materials scientists. New improvements on analytical tools, manipulation and detection of nano-objects, increased computing capacities, or faster time-resolved characterization techniques are exerting a profound impact in the development of this promising field, which is seeing its range of possible applications expanded. We are hoping to offer a portal for some of this exciting new research with a promotional Special Issue of the new Open Access journal, Magnetochemistry, which aims at being a reference among the journals on the old but futuristic discipline after which it has been named.

Dr. Guillem Aromí
Prof. José Antonio Real
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Magnetochemistry is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Spin Crossover (SCO)
  • Fe, Co, Mn coordination chemistry
  • Valence Tautomerism
  • Dioxolene Cobalt complexes
  • Prussian-blue Valence tautomers
  • Light induced SCO (LIESST effect)
  • Guest-exchange Induced SCO
  • Nanostructured SCO materials
  • Transport through single SCO molecules
  • Theoretical calculations on SCO materials
  • Time resolved characterization of the SCO
  • Crystallographic transitions and SCO

Published Papers (21 papers)

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Editorial

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Open AccessEditorial
Special Issue “Spin Crossover (SCO) Research”
Magnetochemistry 2016, 2(3), 28; https://doi.org/10.3390/magnetochemistry2030028 - 04 Jul 2016
Cited by 5
Abstract
This special issue, entitled “Spin Crossover (SCO) Research”, illustrates the current relevance of a focused topic, which is inturn highly versatile. Indeed, the collection of papers presented constitutes a sampler that shows the topical importance of this area by attracting the interest of [...] Read more.
This special issue, entitled “Spin Crossover (SCO) Research”, illustrates the current relevance of a focused topic, which is inturn highly versatile. Indeed, the collection of papers presented constitutes a sampler that shows the topical importance of this area by attracting the interest of many top researchers and how it is approached under a multidisciplinary perspective.[...] Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)

Research

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Open AccessArticle
Surface Effects Leading to Unusual Size Dependence of the Thermal Hysteresis Behavior in Spin-Crossover Nanoparticles
Magnetochemistry 2016, 2(2), 24; https://doi.org/10.3390/magnetochemistry2020024 - 03 May 2016
Cited by 18
Abstract
We analyze the size effect on spin-crossover transition nanoparticles in a 2D Ising-like model subject to a specific ligand-field at the surface. By anisotropic sampling method applied to the finite 2D square Ising lattices with various sizes, we determined the density of macro [...] Read more.
We analyze the size effect on spin-crossover transition nanoparticles in a 2D Ising-like model subject to a specific ligand-field at the surface. By anisotropic sampling method applied to the finite 2D square Ising lattices with various sizes, we determined the density of macro states by scanning the spin configurations. This information, which is independent on the system parameters, is used to exactly calculate the thermal behavior of spin-crossover nanoparticles whose ligand-field of the atoms at the surface is lower than those of the bulk. We found that decreasing the size of the nanoparticles leads to a global increase of the effective interaction, which has the consequence to enhance the width of the thermal hysteresis. This unusual behavior opens a new avenue in controlling the bistability characteristics at small scale, one of the important conditions of applicability of these materials at the nanometric scale. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Spin Transition Kinetics in the Salt [H2N(CH3)2]6[Fe3(L)6(H2O)6] (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate)
Magnetochemistry 2016, 2(2), 20; https://doi.org/10.3390/magnetochemistry2020020 - 28 Mar 2016
Cited by 8
Abstract
The dimethylammonium salt of the FeII polyanionic trimer [Fe3(μ-L)6(H2O)6]6− (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) exhibits a thermally induced spin transition above room temperature with one of the widest hysteresis cycles observed in a spin crossover [...] Read more.
The dimethylammonium salt of the FeII polyanionic trimer [Fe3(μ-L)6(H2O)6]6− (L = 4-(1,2,4-triazol-4-yl)ethanedisulfonate) exhibits a thermally induced spin transition above room temperature with one of the widest hysteresis cycles observed in a spin crossover compound (>85 K). Furthermore, the metastable high-spin (HS) state can be thermally trapped via relatively slow cooling, remaining metastable near room temperature, with a characteristic TTIESST = 250 K (TIESST = temperature-induced excited spin-state trapping). The origin for this unique behavior is still uncertain. In this manuscript, we report detailed studies on the relaxation kinetics of this system in order to disclose the mechanism and cooperativity controlling this process. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Vibrational Coupling of Nearest Neighbors in 1-D Spin Crossover Polymers of Rigid Bridging Ligands. A Nuclear Inelastic Scattering and DFT Study
Magnetochemistry 2016, 2(2), 19; https://doi.org/10.3390/magnetochemistry2020019 - 25 Mar 2016
Cited by 7
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Multistep Relaxations in a Spin-Crossover Lattice with Defect: A Spatiotemporal Study of the Domain Propagation
Magnetochemistry 2016, 2(1), 17; https://doi.org/10.3390/magnetochemistry2010017 - 11 Mar 2016
Cited by 3
Abstract
We study the spatio-temporal formation and spreading of the low-spin state (LS) during the thermal spin transition and the cooperative relaxation of the photo-induced metastable high spin (HS) state at low temperature, in the presence of a structural defect. The model is made [...] Read more.
We study the spatio-temporal formation and spreading of the low-spin state (LS) during the thermal spin transition and the cooperative relaxation of the photo-induced metastable high spin (HS) state at low temperature, in the presence of a structural defect. The model is made of a two-dimensional rectangular-shaped lattice with discrete spins coupled by springs. The investigations are performed for a perfect lattice and a lattice with a hole (simulating the defect) with a fixed size. We found that the presence of the defect affects the thermal equilibrium by reducing the size of the thermal hysteresis at the transition, although the transition temperature remains unchanged. The study of the low-temperature relaxation of the defect-free lattice from HS to LS state indicated the existence of three different regimes of the growth process: (i) a first regime of growth from one corner of the rectangle along the width, then followed by (ii) a second regime of longitudinal propagation at almost constant velocity, and (iii) a third rapid regime when the system feels the surface or the border of the crystal. When a hole is injected inside the lattice, it results in (i) the deformation of the HS/LS interface’s shape when it approaches the defect position; and (ii) the slowing down of its propagation velocity. These results, which are in good agreement with available experimental data, are discussed in terms of elastic energy stored in the system during the relaxation process. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Effects of Internal and External Pressure on the [Fe(PM-PEA)2(NCS)2] Spin-Crossover Compound (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline)
Magnetochemistry 2016, 2(1), 15; https://doi.org/10.3390/magnetochemistry2010015 - 04 Mar 2016
Cited by 7
Abstract
The spin-crossover properties of the strongly cooperative compound [Fe(PM-PEA)2(NCS)2] (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline) have been investigated under external in situ pressure, external ex situ pressure and internal pressure. In situ single-crystal X-ray diffraction investigations under pressure indicate a [...] Read more.
The spin-crossover properties of the strongly cooperative compound [Fe(PM-PEA)2(NCS)2] (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline) have been investigated under external in situ pressure, external ex situ pressure and internal pressure. In situ single-crystal X-ray diffraction investigations under pressure indicate a Spin-Crossover (SCO) at about 400 MPa and room temperature. Interestingly, application of ex situ pressure induces the irreversible enlargement of the hysteresis width, almost independently from the pressure value. Elsewhere, the internal pressure effects are examined through the magnetic and photomagnetic investigations on powders of the solid-solutions based on the Mn ion, [FexMn1−x(PM-PEA)2(NCS)2]. Growing the Mn ratio increases the internal pressure, allowing to control the hysteresis width and the paramagnetic residue but also to enhance the efficiency of the photo-induced SCO. The comparison of the quenching and light-induced behaviors reveals a complex phase-diagram governed by internal pressure, temperature and light. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Periodic Density Functional Calculations in Order to Assess the Cooperativity of the Spin Transition in Fe(phen)2(NCS)2
Magnetochemistry 2016, 2(1), 14; https://doi.org/10.3390/magnetochemistry2010014 - 02 Mar 2016
Cited by 9
Abstract
Periodic density functional calculations combined with the Hubbard model (DFT+U) have been performed for the archetype spin crossover complex Fe(phen) 2 (NCS) 2 with phen = 1,2-phenanthroline. The relative energies of the 16 different configurations of two possible spin states for each of [...] Read more.
Periodic density functional calculations combined with the Hubbard model (DFT+U) have been performed for the archetype spin crossover complex Fe(phen) 2 (NCS) 2 with phen = 1,2-phenanthroline. The relative energies of the 16 different configurations of two possible spin states for each of the four molecules in the unit cell have been calculated in order to determine from first principles the phenomenological interaction parameter Γ of the Slichter-Drickamer model. These kind of calculations may help to predict important spin crossover characteristics like the abruptness or hysteresis of the transition. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessCommunication
Multi-Step in 3D Spin Crossover Nanoparticles Simulated by an Ising Model Using Entropic Sampling Monte Carlo Technique
Magnetochemistry 2016, 2(1), 13; https://doi.org/10.3390/magnetochemistry2010013 - 01 Mar 2016
Cited by 6
Abstract
There are currently extended experimental and theoretical developments of spin crossover nanomaterials, in particular based on coordination polymers for the design of smart applications. In this context, we have reproduced a three step thermal transition in a cubic spin crossover nanomaterial with a [...] Read more.
There are currently extended experimental and theoretical developments of spin crossover nanomaterials, in particular based on coordination polymers for the design of smart applications. In this context, we have reproduced a three step thermal transition in a cubic spin crossover nanomaterial with a system dimension of 5 × 5 × 5 metallic centers. For this purpose, we have calculated, using Monte Carlo Entropic Sampling technique, the density of states of all possible system configurations. In order to take into account the local environment, we have included an additional interaction term in the standard Ising like model. We have then analyzed the role of this new interaction as well as the system size effect variation (from 4 × 4 × 4 to 6 × 6 × 6 metallic centers). Comparison with a 2D SCO system shows that the spin transition still proceeds in three steps but is no longer hysteretic. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Hexakis (propargyl-1H-tetrazole) Iron(II) X2 [X = BF4, ClO4]—Spin Switchable Complexes with Functionalization Potential and the Myth of the Explosive SCO Compound
Magnetochemistry 2016, 2(1), 12; https://doi.org/10.3390/magnetochemistry2010012 - 26 Feb 2016
Cited by 5
Abstract
Spin crossover complexes with ligands suitable for further functionalization could allow for an easy access to multifunctional switchable materials. Within this context, we recently characterized the Fe(II) SCO complexes of propargyl-1H-tetrazole. Although the design of the ligand seems similar to the [...] Read more.
Spin crossover complexes with ligands suitable for further functionalization could allow for an easy access to multifunctional switchable materials. Within this context, we recently characterized the Fe(II) SCO complexes of propargyl-1H-tetrazole. Although the design of the ligand seems similar to the one of the well-known propyl-1H-tetrazole, the spin transition behavior is notably different. Both compounds reported herein feature a gradual spin transition with a T1/2 shifted to lower temperatures, compared to the more flexible propyl-ligand. Due to the potential instable structure of these compounds, especially of the perchlorate complex, we also investigated our compounds with regard to their sensitivity against thermal and mechanical stress. These experiments led to the conclusion that the proper handling includes no enhanced risk of explosive decomposition. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessCommunication
CdTe Quantum Dot Fluorescence Modulation by Spin Crossover
Magnetochemistry 2016, 2(1), 11; https://doi.org/10.3390/magnetochemistry2010011 - 25 Feb 2016
Cited by 11
Abstract
Nanocomposite materials containing Cadmium Telluride (CdTe) nanocrystals and [Fe(H-trz)2(trz)]BF4 nanoparticles were synthesized and investigated for the coupling between their photoluminescent and spin crossover properties. The bright CdTe emission around 550 nm was found to decrease reversibly when switching the ferrous [...] Read more.
Nanocomposite materials containing Cadmium Telluride (CdTe) nanocrystals and [Fe(H-trz)2(trz)]BF4 nanoparticles were synthesized and investigated for the coupling between their photoluminescent and spin crossover properties. The bright CdTe emission around 550 nm was found to decrease reversibly when switching the ferrous complex from the high spin (HS) to the low spin (LS) state, which was attributed to the spectral overlap of the luminescence with the absorption of the complex in the latter electronic configuration. A significant irreversible change of the luminescence signal (photobleaching) was also observed both in emission intensity and lifetime measurements. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Rational Control of Spin-Crossover Particle Sizes: From Nano- to Micro-Rods of [Fe(Htrz)2(trz)](BF4)
Magnetochemistry 2016, 2(1), 10; https://doi.org/10.3390/magnetochemistry2010010 - 24 Feb 2016
Cited by 18
Abstract
The spin-crossover (SCO) materials based on iron (II) and triazole ligands can change their spin state under an external perturbation such as temperature, pressure or light irradiation, exhibiting notably large hysteresis in their physical properties’ transitions. If these aspects are investigated for decades, [...] Read more.
The spin-crossover (SCO) materials based on iron (II) and triazole ligands can change their spin state under an external perturbation such as temperature, pressure or light irradiation, exhibiting notably large hysteresis in their physical properties’ transitions. If these aspects are investigated for decades, it is only in the recent years that the design of SCO particles has attracted the attention of the scientific community with increasing interest focusing on the possibility of getting wide ranges of sizes and shapes of nanoparticles. In this context, we rationalized the reverse-micellar synthesis, thanks to the scrutiny of the experimental parameters, to produce SCO particles with controlled size and shape. This approach has been performed for the reference one-dimensional (1D) polymeric spin-crossover compound of formula [Fe(Htrz)2(trz)](BF4). A synergetic effect of both time and temperature is revealed as being of paramount importance to control the final particle size. Consequently, under well-defined experimental conditions, we can now offer rod-shaped SCO particles with lengths ranging from 75 to 1000 nm. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
A High Pressure Investigation of the Order-Disorder Phase Transition and Accompanying Spin Crossover in [FeL12](ClO4)2 (L1 = 2,6-bis{3-methylpyrazol-1-yl}-pyrazine)
Magnetochemistry 2016, 2(1), 9; https://doi.org/10.3390/magnetochemistry2010009 - 17 Feb 2016
Cited by 5
Abstract
A high pressure single crystal X-ray diffraction and Raman spectroscopy study has revealed a similar mechanism for both thermal and pressure-induced spin crossover in [FeL12](ClO4)2 (L1 = 2,6-bis{3-methylpyrazol-1-yl}-pyrazine) and the concomitant anion order-disorder transition. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Spin-Crossover Behavior of Hofmann-Type-Like Complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O Depending on Guest Species
Magnetochemistry 2016, 2(1), 8; https://doi.org/10.3390/magnetochemistry2010008 - 16 Feb 2016
Cited by 7
Abstract
A newly prepared metal complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O, which was estimated to have a structure similar to the Hofmann-type clathrate host, changed its color from orange to deep orange and yellow on exposure to ethanol and acetone vapor, respectively, [...] Read more.
A newly prepared metal complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O, which was estimated to have a structure similar to the Hofmann-type clathrate host, changed its color from orange to deep orange and yellow on exposure to ethanol and acetone vapor, respectively, and the respective samples showed thermally induced two-step and one-step spin transitions. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Structure and Magnetic Properties of the Spin Crossover Linear Trinuclear Complex [Fe3(furtrz)6(ptol)2(MeOH)4]·4(ptol)·4(MeOH) (furtrz: furanylidene-4H-1,2,4-triazol-4-amine ptol: p-tolylsulfonate)
Magnetochemistry 2016, 2(1), 7; https://doi.org/10.3390/magnetochemistry2010007 - 16 Feb 2016
Cited by 10
Abstract
The furan-functionalised 1,2,4-triazole ligand furanylidene-4H-1,2,4-triazol-4-amine (furtrz) has been incorporated into the trinuclear complex Fe3(furtrz)6(ptol)2(MeOH)4]·4(ptol)·4(MeOH) (ptol = p-tolylsulfonate) composed of μ1,2-triazole bridges between iron(II) sites, as per one-dimensional chain materials, and terminally coordinated [...] Read more.
The furan-functionalised 1,2,4-triazole ligand furanylidene-4H-1,2,4-triazol-4-amine (furtrz) has been incorporated into the trinuclear complex Fe3(furtrz)6(ptol)2(MeOH)4]·4(ptol)·4(MeOH) (ptol = p-tolylsulfonate) composed of μ1,2-triazole bridges between iron(II) sites, as per one-dimensional chain materials, and terminally coordinated ptol anions and methanol molecules. Magnetic susceptibility measurements reveal a gradual single-step spin crossover (SCO) behavior of one third of the iron(II) sites per trinuclear unit. Single-crystal X-ray diffraction below the transition (90 K) shows the central iron(II) sites undergo a HS to LS transition and the peripheral ones remain HS (HS = high spin; LS = low spin). This is a rare example of a cationic trinuclear SCO material where the discrete unit includes bound anions. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Disclosing the Ligand- and Solvent-Induced Changes on the Spin Transition and Optical Properties of Fe(II)-Indazolylpyridine Complexes
Magnetochemistry 2016, 2(1), 6; https://doi.org/10.3390/magnetochemistry2010006 - 05 Feb 2016
Cited by 6
Abstract
The family of the spin crossover (SCO) compounds based on the 1-bpp unit has furnished striking examples of how subtle changes in the crystal packing have important consequences in their spin transition. Small modifications of the 1-bpp unit itself have been recently reported, [...] Read more.
The family of the spin crossover (SCO) compounds based on the 1-bpp unit has furnished striking examples of how subtle changes in the crystal packing have important consequences in their spin transition. Small modifications of the 1-bpp unit itself have been recently reported, obtaining the indazolyl and pirazolyl derivatives [FeII(1-bip)]2+ (1, 1-bip = 2,6-bis(indazol-1-yl)pyridine), [FeII(1,2-bip)]2+ (2, 1,2-bip = 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine), [FeII(2-bip)]2+ (3, 2-bip = 2,6-bis(indazol-2-yl)pyridine), [FeII(1-ipp)]2+ (4, 1-ipp = 2-(indazol-1-yl)-6-(pyrazol-1-yl)pyridine) and [FeII(2-ipp)]2+ (5, 2-ipp = 2-(indazol-2-yl)-6-(pyrazol-1-yl)pyridine). In this work we study the consequences of a change in the ligand structure and solvent on the SCO of 15. More specifically, we demonstrate that their different behavior is not due to an intraligand H···H contact, as suggested experimentally, but to an unfavorable arrangement of the FeN6 core that some of the ligands might create, which destabilizes their Low Spin (LS) state structure and, thus, alters the transition temperature. Further, by means of solid state calculations, we disclose the effect of the solvent on the structure and crystal cohesion of the crystals. Finally, we analyze the emission and adsorption properties of 15, with special interest in the evolution of the absorption spectroscopy of the ligands upon complexation, and its relation with the spin multiplicity of the iron ion. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Heteroleptic Iron(III) Spin Crossover Complexes; Ligand Substitution Effects
Magnetochemistry 2016, 2(1), 3; https://doi.org/10.3390/magnetochemistry2010003 - 22 Jan 2016
Cited by 6
Abstract
Heteroleptic iron(III) complexes of formula [Fe(qsal-Cl)(thsa)]∙nMeCN have been synthesized; [Fe(qsal-Cl)(thsa)]∙MeCN, 1 and [Fe(qsal-Cl)(thsa)], 2. The latter can be obtained by slow evaporation of solutions of compound 1 under ambient conditions, a rare occurrence in nonporous compounds. 1 interestingly shows a [...] Read more.
Heteroleptic iron(III) complexes of formula [Fe(qsal-Cl)(thsa)]∙nMeCN have been synthesized; [Fe(qsal-Cl)(thsa)]∙MeCN, 1 and [Fe(qsal-Cl)(thsa)], 2. The latter can be obtained by slow evaporation of solutions of compound 1 under ambient conditions, a rare occurrence in nonporous compounds. 1 interestingly shows a unique magnetic profile over the de-solvation temperature range, 300-350 K, in the first cycle, and becomes stable after the third cycle with a hysteresis width of about 20 K. Different de-solvation techniques used on compound 1 give rise to various stable de-solvated phases. Consequently, distinct magnetic profiles, with a larger hysteresis width of about 30 K, are present. Cl substitution on the qsal ligand introduces C–H∙∙∙Cl and P4AE interactions into the structure which are absent in the related unsubstituted compound, [Fe(qsal)(thsa)]∙0.5MeCN, 3. Comparisons in structural packing, as well as spin crossover properties between unsubstituted and Cl-substituted ligand compounds, are discussed. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Abrupt Spin Transition and Chiral Hydrogen-Bonded One-Dimensional Structure of Iron(III) Complex [FeIII(Him)2(hapen)]SbF6 (Him = imidazole, H2hapen = N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine)
Magnetochemistry 2015, 1(1), 72-82; https://doi.org/10.3390/magnetochemistry1010072 - 11 Dec 2015
Cited by 3
Abstract
Solvent-free spin crossover (SCO) iron(III) complex, [FeIII(Him)2(hapen)]SbF6 (Him = imidazole, H2hapen = N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine), is synthesized. The FeIII ion has an octahedral coordination geometry, with N2O2 donor atoms of hapen and N [...] Read more.
Solvent-free spin crossover (SCO) iron(III) complex, [FeIII(Him)2(hapen)]SbF6 (Him = imidazole, H2hapen = N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine), is synthesized. The FeIII ion has an octahedral coordination geometry, with N2O2 donor atoms of hapen and N2 atoms of two imidazoles at the axial positions. The saturated five-membered chelate ring of hapen moiety assumes a gauche-type δ- or λ-conformation to give chiral species of δ-[FeIII(Him)2(hapen)]+ or λ-[FeIII(Him)2(hapen)]+. One imidazole is hydrogen-bonded to phenoxo oxygen atom of hapen of the adjacent unit to give a hydrogen-bonded chiral one-dimensional structure, {δ-[FeIII(Him)2(hapen)]+}1∞ or {λ-[FeIII(Him)2(hapen)]+}1∞. The adjacent chains with the opposite chiralities are arrayed alternately. The temperature dependences of the magnetic susceptibilities revealed an abrupt one-step spin transition between high-spin (S = 5/2) and low-spin (S = 1/2) states at the spin transition temperature of T1/2 = 105 K. The crystal structures were determined at 296 and 100 K, where the populations of HS:LS of high- and low-spin ratio are evaluated to be 1:0 and 0.3:0.7, respectively, based on magnetic measurements. During the spin transition from 296 K to 100 K, the average Fe–N distance and O–Fe–O angle decrease to a regular octahedron by 0.16 Å and 13.4°, respectively. The structural change in the coordination environment is transmitted to the adjacent spin crossover (SCO) sites along the chiral 1D chain through hydrogen-bonds. The abrupt SCO profile and the spin transition temperature for the isomorphous compounds [FeIII(Him)2(hapen)]Y (Y = PF6, AsF6, SbF6) are ascribed to the chiral hydrogen-bonded 1D structure and chain-anion interaction. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessCommunication
Spin-Crossover Hysteresis of [FeII(LHiPr)2(NCS)2] (LHiPr = N-2-Pyridylmethylene-4-Isopropylaniline) Accompanied by Isopropyl Conformation Isomerism
Magnetochemistry 2015, 1(1), 17-27; https://doi.org/10.3390/magnetochemistry1010017 - 20 Nov 2015
Cited by 9
Abstract
[FeII(LHiPr)2(NCS)2] (LHiPr = N-2-pyridylmethylene-4-isopropylaniline) showed an abrupt spin-crossover (SCO) at T1/2↓ = 154 K on cooling and at T1/2↑ = 167 K on heating. The thermal hysteresis [...] Read more.
[FeII(LHiPr)2(NCS)2] (LHiPr = N-2-pyridylmethylene-4-isopropylaniline) showed an abrupt spin-crossover (SCO) at T1/2↓ = 154 K on cooling and at T1/2↑ = 167 K on heating. The thermal hysteresis with a width of 13 K is related with the structural solid-state phase transition. The space group was unchanged as P21/n with Z = 8, and there are two crystallographically independent molecules in a unit cell at 130 and 180 K. The two iron (II) sites synchronously underwent the SCO. The most drastic structural change across the SCO was found in the conformation isomerization of an isopropyl group. Namely, rotation around the C(sp2)–C(sp3) bond by ca. 120° takes place during the SCO. There is no structural disorder in the high-temperature phase. The thermal hysteresis probably originates in the bulk isomerization requiring considerable activation energy in the crystalline solid. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessArticle
Synthesis of 4-Hydroxy-2,6-di(pyrazol-1-yl)pyridine, and the Spin State Behaviour of Its Iron(II) Complex Salts
Magnetochemistry 2015, 1(1), 3-16; https://doi.org/10.3390/magnetochemistry1010003 - 23 Oct 2015
Cited by 5
Abstract
Treatment of 4-hydroxy-2,6-dibromopyridine with four equivalent of deprotonated pyrazole in hot diglyme affords 4-hydroxy-2,6-di(pyrazol-1-yl)pyridine (L) in low yield. The three complex salts [FeL2]X2 (X = BF4, 1; X = [...] Read more.
Treatment of 4-hydroxy-2,6-dibromopyridine with four equivalent of deprotonated pyrazole in hot diglyme affords 4-hydroxy-2,6-di(pyrazol-1-yl)pyridine (L) in low yield. The three complex salts [FeL2]X2 (X = BF4, 1; X = ClO4, 2; X = PF6, 3) have been prepared, and crystallographically characterised as their methanol solvates. The solvate structures contain complexes that are fully high-spin (1 and 3), or in a mixed high:low spin state population at 150 K (2). Bulk samples of 1 and 2 obtained from methanol/diethyl ether contain a second, minor crystal phase that exhibits an abrupt spin-transition near 200 K. Recrystallisation of 1 and 2 from nitromethane/diethyl ether affords powder samples that are highly enriched in this spin-transition phase. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Review

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Open AccessReview
Charge Transport and Electrical Properties of Spin Crossover Materials: Towards Nanoelectronic and Spintronic Devices
Magnetochemistry 2016, 2(1), 18; https://doi.org/10.3390/magnetochemistry2010018 - 11 Mar 2016
Cited by 64
Abstract
In this paper, we present a comprehensive review of research on electrical and charge transport properties of spin crossover complexes. This includes both the effect of spin-state switching on the dielectric permittivity and electrical conductivity of the material and vice versa the influence [...] Read more.
In this paper, we present a comprehensive review of research on electrical and charge transport properties of spin crossover complexes. This includes both the effect of spin-state switching on the dielectric permittivity and electrical conductivity of the material and vice versa the influence of an applied electrical field (or current) on the spin-state of the system. The survey covers different size scales from bulk materials and thin films to nanoparticles and single molecules and embraces the presentation of several device prototypes and hybrid materials as well. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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Open AccessFeature PaperReview
Symmetry Breaking in Iron(II) Spin-Crossover Molecular Crystals
Magnetochemistry 2016, 2(1), 16; https://doi.org/10.3390/magnetochemistry2010016 - 11 Mar 2016
Cited by 33
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) ↔ low-spin (LS) phase transitions accompanied by crystallographic symmetry breaking (CSB). Particular interest has been focused on a variety of [...] Read more.
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) ↔ 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. Full article
(This article belongs to the Special Issue Spin Crossover (SCO) Research)
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