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Magnetochemistry
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Spin-Crossover Beyond the Immediate Tribute
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Spin-Crossover Beyond the Immediate Tribute

A special issue of Magnetochemistry (ISSN 2312-7481). This special issue belongs to the section "Spin Crossover and Spintronics".

Deadline for manuscript submissions: closed (30 May 2019) | Viewed by 42644

Special Issue Editors

Prof. Dr. Philippe GUIONNEAU

E-Mail Website
Guest Editor
ICMCB, CNRS, University of Bordeaux, UMR5026, 33608 Pessac - FRANCE
Interests: My main research efforts are focused on the investigation of the relationships between the structural and physical properties in solids with a preference, but not exclusively, for molecular materials. These studies fall within the field of expertise of crystallography and address the different scales of matter, distinct environments (temperature, pressure, light) and various types of samples (crystals, nanoparticles, powders, films, raw material) in connection with magnetism, conductivity and optical features. Examples of the investigated fields are molecular superconductors, molecular magnets, spin-crossover phenomena and organic–inorganic hybrid materials
Keywords: Crystallography, X-rays, Solid-state, Phase transition, High-pressure, Low-temperature, Molecular crystals, Spin-crossover, Multi-functional materials
Dr. Guillaume CHASTANET

E-Mail Website
Guest Editor
ICMCB, CNRS, University of Bordeaux, UMR5026, 33608 Pessac - FRANCE
Interests: Switchable molecules, especially spin crossover molecules, constitute my main research topic, ranging from molecular solid-state chemistry to the molecular materials sciences. The story of a compound starts with the design of molecule (the ligand and the coordination complex) and its integration in a molecular crystal. The interplay between the molecular and the material scales leads to a wide range of properties (ferro– and antiferro–elastic interactions, elastic frustration, bidirectional photoswitching, phase transitions, polymorphism, etc.). Photoswitching is particularly attractive since unusual states can be reached, at various scales (from molecules to materials, from crystals to nanoparticles, from femtoseconds to hours).

Special Issue Information

Dear Colleagues,

Borders are the melting pot of cultural effervescence; they are also places of perdition where danger lurks. This observation applies to science; it is indeed often at the borders of well-recognized scientific fields that ideas and major improvements take place, even though care must be taken not to get lost in the background. Spin-crossover (SCO) is a topic that is truly located at the crossroads of a wide variety of approaches and characterization techniques, a large panel of research fields and communities, as well as diverse targets ranging from fundamental questioning to practical developments. Consequently, working on the SCO phenomenon can potentially lead to advancements in knowledge and know-how that turn out to be relevant in other, sometimes unanticipated scientific fields. The open access journal Magnetochemistry has earlier devoted a Special Issue to SCO (January 2016). The success of the latter and the high quality of the published results first illustrated the above arguments and, second, urged the dedication of another Special Issue to SCO, notably because of the amazing and growing amount of progress made on this exciting topic. This Special Issue is therefore devoted to Spin-CrossOver, focusing on the promotion of its multi-disciplinary aspects, and providing authors with a place to present their latest discoveries and the opportunity to offer a tribute beyond their usual audience.

Prof. Dr. Philippe GUIONNEAU
Dr. Guillaume CHASTANET
Guest Editors

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Published Papers (9 papers)

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Research

14 pages, 2739 KiB  
Article
The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover
by Jianfang Wu, Carmen Sousa and Coen de Graaf
Magnetochemistry 2019, 5(3), 49; https://doi.org/10.3390/magnetochemistry5030049 - 2 Sep 2019
Cited by 10 | Viewed by 3763
Abstract
Spin crossover in transition metal complexes can be studied in great detail with computational chemistry. Over the years, the understanding has grown that the relative stability of high-spin (HS) versus low-spin (LS) states is a subtle balance of many factors that all need [...] Read more.
Spin crossover in transition metal complexes can be studied in great detail with computational chemistry. Over the years, the understanding has grown that the relative stability of high-spin (HS) versus low-spin (LS) states is a subtle balance of many factors that all need to be taken into account for a reliable description. Among the different contributions, the zero-point energy (ZPE) and the entropy play key roles. These quantities are usually calculated assuming a harmonic oscillator model for the molecular vibrations. We investigated the impact of including anharmonic corrections on the ZPE and the entropy and indirectly on the critical temperature of spin crossover. As test systems, we used a set of ten Fe(II) complexes and one Fe(III) complex, covering different coordination modes (mono-, bi-, and tri-dentate ligands), decreasing coordination number upon spin crossover, coordination by second- and third-row atoms, and changes in the oxidation state. The results show that the anharmonicity has a measurable effect, but it is in general rather small, and tendencies are not easily recognized. As a conclusion, we put forward that for high precision results, one should be aware of the anharmonic effects, but as long as computational chemistry is still struggling with other larger factors like the influence of the environment and the accurate determination of the electronic energy difference between HS and LS, the anharmonicity of the vibrational modes is a minor concern. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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21 pages, 5382 KiB  
Article
Iron(III) Azadiphenolate Compounds in a New Family of Spin Crossover Iron(II)–Iron(III) Mixed-Valent Complexes
by Wasinee Phonsri, David S. Macedo, Barnaby A. I. Lewis, Declan F. Wain and Keith S. Murray
Magnetochemistry 2019, 5(2), 37; https://doi.org/10.3390/magnetochemistry5020037 - 12 Jun 2019
Cited by 7 | Viewed by 4290
Abstract
A new family of mixed valent, double salt spin crossover compounds containing anionic FeIII and cationic FeII compounds i.e., [FeII{(pz)3CH}2][FeIII(azp)2]2·2H2O (4), [FeII(TPPZ)2 [...] Read more.
A new family of mixed valent, double salt spin crossover compounds containing anionic FeIII and cationic FeII compounds i.e., [FeII{(pz)3CH}2][FeIII(azp)2]2·2H2O (4), [FeII(TPPZ)2][FeIII(azp)2]2]·H2O (5) and [FeII(TPPZ)2][FeIII(azp)2]2]·H2O·3MeCN (6) (where (pz)3CH = tris-pyrazolylmethane, TPPZ = 2,3,5,6, tetrapyridylpyrazine and azp2− = azadiphenolato) has been synthesized and characterised. This is the first time that the rare anionic spin crossover species, [FeIII(azp)2]−, has been used as an anionic component in double salts complexes. Single crystal structures and magnetic studies showed that compound 6 exhibits a spin transition relating to one of the FeIII centres of the constituent FeII and FeIII sites. Crystal structures of the anionic and cationic precursor complexes were also analysed and compared to the double salt products thus providing a clearer picture for future crystal design in double spin crossover materials. We discuss the effects that the solvent and counterion had on the crystal packing and spin crossover properties. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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14 pages, 2207 KiB  
Article
Bilayer Thin Films That Combine Luminescent and Spin Crossover Properties for an Efficient and Reversible Fluorescence Switching
by Alin-Ciprian Bas, Xavier Thompson, Lionel Salmon, Christophe Thibault, Gábor Molnár, Oleg Palamarciuc, Lucie Routaboul and Azzedine Bousseksou
Magnetochemistry 2019, 5(2), 28; https://doi.org/10.3390/magnetochemistry5020028 - 1 May 2019
Cited by 9 | Viewed by 4992
Abstract
We report on the vacuum thermal deposition of bilayer thin films of the luminescent complex Ir(ppy)3, tris[2-phenylpyridinato-C2,N]iridium(III), and the spin crossover complex [Fe(HB(tz)3)2], bis[hydrotris(1,2,4-triazol-1-yl)borate]iron(II). Switching the spin state of iron ions from the low spin to the [...] Read more.
We report on the vacuum thermal deposition of bilayer thin films of the luminescent complex Ir(ppy)3, tris[2-phenylpyridinato-C2,N]iridium(III), and the spin crossover complex [Fe(HB(tz)3)2], bis[hydrotris(1,2,4-triazol-1-yl)borate]iron(II). Switching the spin state of iron ions from the low spin to the high spin state around 337 K leads to a reversible jump of the luminescence intensity, while the spectrum shape and the luminescence lifetime remain unchanged. The luminescence modulation occurs due to the different UV light absorption properties of the iron complex in the two spin states and its magnitude can therefore be precisely adjusted by varying the film thickness. These multilayer luminescence switches hold potential for micro- and nanoscale thermal sensing and imaging applications. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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13 pages, 2571 KiB  
Article
Solution-State Spin Crossover in a Family of [Fe(L)2(CH3CN)2](BF4)2 Complexes
by Benjamin H. Wilson, Hayley S. Scott, Rosanna J. Archer, Corine Mathonière, Rodolphe Clérac and Paul E. Kruger
Magnetochemistry 2019, 5(2), 22; https://doi.org/10.3390/magnetochemistry5020022 - 1 Apr 2019
Cited by 4 | Viewed by 4593
Abstract
We report herein on five new Fe(II) complexes of general formula [Fe(L)2(NCCH3)2](BF4)2•xCH3CN (L = substituted 2-pyridylimine-based ligands). The influence of proximally located electron withdrawing groups (e.g., NO2, [...] Read more.
We report herein on five new Fe(II) complexes of general formula [Fe(L)2(NCCH3)2](BF4)2•xCH3CN (L = substituted 2-pyridylimine-based ligands). The influence of proximally located electron withdrawing groups (e.g., NO2, CN, CF3, Cl, Br) bound to coordinated pyridylimine ligands has been studied for the effect on spin crossover in their Fe(II) complexes. Variable-temperature UV-visible spectroscopic studies performed on complexes with more strongly electronegative ligand substituents revealed spin crossover (SCO) in the solution, and thermodynamic parameters associated with the spin crossover were estimated. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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15 pages, 12477 KiB  
Article
Evidence of Photo-Thermal Effects on the First-Order Thermo-Induced Spin Transition of [{Fe(NCSe)(py)2}2(m-bpypz)] Spin-Crossover Material
by Kamel Boukheddaden, Houcem Fourati, Yogendra Singh and Guillaume Chastanet
Magnetochemistry 2019, 5(2), 21; https://doi.org/10.3390/magnetochemistry5020021 - 1 Apr 2019
Cited by 17 | Viewed by 3792
Abstract
We have investigated by means of optical microscopy and magnetic measurements the first-order thermal spin transition of the [{Fe(NCSe)(py)2}2(m-bpypz)] spin-crossover compound under various shining intensities, far from the light-induced spin-state trapping region. We found evidence of photo-heating effects on [...] Read more.
We have investigated by means of optical microscopy and magnetic measurements the first-order thermal spin transition of the [{Fe(NCSe)(py)2}2(m-bpypz)] spin-crossover compound under various shining intensities, far from the light-induced spin-state trapping region. We found evidence of photo-heating effects on the thermally-induced hysteretic response of this spin-crossover material, thus causing the shift of the thermal hysteresis to lower temperature regions. The experimental results are discussed in terms of the apparent crystal temperature and are analyzed theoretically using two evolution equations of motion, written on the high-spin (HS) fraction and heat balance between the crystal and the thermal bath. A very good qualitative agreement was found between experiment and theory in the stationary regime, explaining the experimental observations well and identifying the key factors governing these photo-thermal effects. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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14 pages, 1833 KiB  
Article
Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties
by Merzouk Halit, Mélissa Roger, Véronique Patinec, Said Yefsah, Carlos J. Gómez-García and Smail Triki
Magnetochemistry 2019, 5(1), 19; https://doi.org/10.3390/magnetochemistry5010019 - 7 Mar 2019
Cited by 2 | Viewed by 4143
Abstract
The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4) [...] Read more.
The unsymmetrical ligand 1-(2-aminophenyl)-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane (L6) has been prepared and characterized by NMR spectroscopy. The L6 ligand is based on the triazamacrocycle (tacn) ring that is functionalized by two flexible 2-pyridylmethyl and one rigid 2-aminophenyl groups. Reaction of this ligand with Fe(ClO4)2·xH2O led to the complex [Fe(L6)](ClO4)2 (1), which was characterized as the first Fe(II) complex based on the unsymmetrical N-functionalized tacn ligand. The crystal structure revealed a discrete monomeric [FeL6]2+ entity in which the unsymmetrical N-functionalized triazacyclononane molecule (L6) acts as hexadentate ligand. As observed in the few parent examples that are based on the symmetrical N-functionalized tacn ligands, the triazacyclononane ring is facially coordinated and the N-donor atoms of the three functional groups (two pyridine and one aniline groups) are disposed in the same side of the tacn ring, leading to a distorted FeN6 environment. The magnetic studies of 1 revealed the presence of an incomplete spin crossover (SCO) transition above 425 K, whose progress would be prevented by a very exothermic thermal decomposition at ca. 472 K, as shown by thermogravimetric and DSC measurements. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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Graphical abstract

18 pages, 4219 KiB  
Article
Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes
by Iurii Galadzhun, Rafal Kulmaczewski and Malcolm A. Halcrow
Magnetochemistry 2019, 5(1), 9; https://doi.org/10.3390/magnetochemistry5010009 - 1 Feb 2019
Cited by 5 | Viewed by 3222
Abstract
Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N′-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in [...] Read more.
Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N′-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in acetone yielded the corresponding [FeL2][BF4]2 complex salts. Four of the new ligands and four of the complexes have been crystallographically characterised. Particularly noteworthy are two polymorphs of [Fe(L3)2][BF4]2·2MeNO2 (L3 = 3,4-dimethoxyphenyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), one of which is crystallographically characterised as high-spin while the other exhibits the onset of spin-crossover above room temperature. The other complexes are similarly low-spin at low temperature but exhibit gradual spin-crossover on heating, except for an acetone solvate of [Fe(L5)2][BF4]2 (L5 = benzyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), which exhibits a more abrupt spin-transition at T½ = 273 K with 9 K thermal hysteresis. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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12 pages, 11077 KiB  
Article
Interfacial Spin Manipulation of Nickel-Quinonoid Complex Adsorbed on Co(001) Substrate
by Indukuru Ramesh Reddy, Peter M. Oppeneer and Kartick Tarafder
Magnetochemistry 2019, 5(1), 2; https://doi.org/10.3390/magnetochemistry5010002 - 24 Dec 2018
Cited by 5 | Viewed by 8583
Abstract
We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory + U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin [...] Read more.
We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory + U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin S = 0 in the gas phase to high-spin S ≈ 1 when adsorbed on the Co(001) surface. A strong covalent interaction of the quinonoid rings and surface atoms leads to an increase of the Ni–O(N) bond lengths in the chemisorbed molecule that support the spin-state switching. Our DFT+U calculations show that the molecule is ferromagnetically coupled to the substrate. The Co surface–Ni center exchange mechanism was carefully investigated. We identified an indirect exchange interaction via the quinonoid ligands that stabilizes the molecule’s spin moment in ferromagnetic alignment with the Co surface magnetization. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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15 pages, 6018 KiB  
Article
Abrupt Spin Crossover Behavior in a Linear N1,N2-Triazole Bridged Trinuclear Fe(II) Complex
by Ai-Min Li, Tim Hochdörffer, Juliusz A. Wolny, Volker Schünemann and Eva Rentschler
Magnetochemistry 2018, 4(3), 34; https://doi.org/10.3390/magnetochemistry4030034 - 7 Aug 2018
Cited by 6 | Viewed by 4110
Abstract
The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex [FeII3(pyrtrz)6(TsO)6]·10H2O·2CH3OH (C2) and its analogue binuclear [FeII2(pyrtrz)5(SCN)4 [...] Read more.
The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex [FeII3(pyrtrz)6(TsO)6]·10H2O·2CH3OH (C2) and its analogue binuclear [FeII2(pyrtrz)5(SCN)4]·7H2O (C1), are reported here. These two compounds are synthesized based on the pyrrolyl functionalized Schiff base 1,2,4-triazole ligand 4-((1H-pyrrol-2-yl)methylene-amino)-4H-1,2,4-triazole (pyrtrz), which represent rare discrete multi-nuclear species, with µ2-N1,N2-triazole bridges linking the FeII centers. DC magnetic susceptibility measurements revealed an abrupt single-step spin crossover (SCO) behavior for compound 2 on the central FeII site and single-crystal X-ray diffraction (173 K) showed that this compound crystallizes in the monoclinic space group (P21/c), and multiple intramolecular interactions were found responsible for the abrupt transition. Compound 1 is a binuclear complex with thiocyanate as terminal ligands. This compound stays in high spin state over the whole temperature range and displays weak antiferromagnetic exchange coupling. Full article
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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