Special Issue "Spin-Crossover Beyond the Immediate Tribute"

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

Deadline for manuscript submissions: 30 April 2019

Special Issue Editors

Guest Editor
Prof. Dr. Philippe GUIONNEAU

ICMCB, CNRS, University of Bordeaux, UMR5026, 33608 Pessac - FRANCE
Website | E-Mail
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
Guest Editor
Dr. Guillaume CHASTANET

ICMCB, CNRS, University of Bordeaux, UMR5026, 33608 Pessac - FRANCE
Website | E-Mail
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

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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 350 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.

Published Papers (4 papers)

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Research

Open AccessArticle Spin Cross-Over (SCO) Complex Based on Unsymmetrical Functionalized Triazacyclononane Ligand: Structural Characterization and Magnetic Properties
Magnetochemistry 2019, 5(1), 19; https://doi.org/10.3390/magnetochemistry5010019
Received: 21 December 2018 / Revised: 23 February 2019 / Accepted: 25 February 2019 / Published: 7 March 2019
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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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Open AccessArticle Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes
Magnetochemistry 2019, 5(1), 9; https://doi.org/10.3390/magnetochemistry5010009
Received: 20 December 2018 / Revised: 18 January 2019 / Accepted: 22 January 2019 / Published: 1 February 2019
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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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Open AccessArticle Interfacial Spin Manipulation of Nickel-Quinonoid Complex Adsorbed on Co(001) Substrate
Magnetochemistry 2019, 5(1), 2; https://doi.org/10.3390/magnetochemistry5010002
Received: 29 November 2018 / Revised: 20 December 2018 / Accepted: 21 December 2018 / Published: 24 December 2018
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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 S= [...] 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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Open AccessArticle Abrupt Spin Crossover Behavior in a Linear N1,N2-Triazole Bridged Trinuclear Fe(II) Complex
Magnetochemistry 2018, 4(3), 34; https://doi.org/10.3390/magnetochemistry4030034
Received: 28 June 2018 / Revised: 31 July 2018 / Accepted: 1 August 2018 / Published: 7 August 2018
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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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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Title: Nuclear inelastic scattering and DFT study of the 1D and 3D spin crossover complexes of Fe(II) 4-urea 1,2,4-triazoles
Authors: Juliusz Wolny and Volker Schuenemann

2. Title: Bifunctional Fe(II) SCO-complexes based on  w-(1H-tetrazol-1-yl) carboxylic acids
Authors: Willi Zeni, Christian Knoll, Jan M. Welch, Michael Reissner, Gerald Giester, Danny Müller,* Peter Weinberger
Abstract: w-(1H-tetrazol-1-yl) carboxylic acids with C2-C4 alkyl-chains were used as ditopic ligands for preparation of spin-switchable Fe(II) complexes. From the carboxylic acids originates a stabilizing hydrogen-bonding network, interconnecting the Fe(II)-sites and resulting in a highly cooperative spin state transition. Based on the extension of the chain-length, a weakening of the molecular interaction correlates with the decreasing abruptness of the spin crossover.

3. Title: The influence on spin state and spin crossover behavior of tripodal complexes of tris(2-aminoethyl)amine and relatives with first row transition metal ions
Author: Greg Brewer
Abstract: Tris(2-aminoethyl)amine and its close relatives undergo Schiff base condensations with a variety of aldehydes, salicylaldehyde, pyrolle-2-carboxaldehyde, imidazole carboxaldehydes and pyrazole carboxaldehydes to give tripodal ligands that can bind to a metal to give octahedral or capped octahedral (CN=7) complexes. The d^4-d^7 metals can be either high spin or low spin. There are a number of factors that influence spin state selection with these versatile ligands. These include the donor set, the protonation state of ionizable aldehydes, the length of thy alkyl chain of the tripodal nitrogen atom and the isomeric identity of imidazole or pyrazole carboxaldehydes, Evidence of spin state can be obtained from variable temperature magnetic susceptibility, structural data, ESR, and Mossbauer. DFT can also be used to predict spin state of complexes or complexes which are close to the spin crossover point. Some of these complexes form supramolecular systems, adding an additional twist to the spin crossover phenomenon.   

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