Scientists manage to chemically adjust the electronic properties of new layered materials

As part of an international collaboration, scientists from the Centre de Recherche Paul Pascal, the Institut de Chimie de la Matière Condensée de Bordeaux (CNRS/University of Bordeaux) and the ESRF have shown how to chemically adjust the electronic structure of a layered metal-organic material to control its physical properties, such as electrical conduction and magnetism. This work, published in the journal Nature Communications, paves the way for the design of a new generation of conducting, and potentially superconducting, molecule-based materials.

Molecule-based components proposed for integration into our miniaturized electronic equipment must possess perfectly controlled magnetic and electrical conduction properties. Their ability to be semiconductors, conductors or even insulators, while exhibiting remarkable magnetic properties, makes them very good candidates for integration into future devices for spintronic applications. This is why chemists and physicists are working together to understand the precise role of physicochemical parameters at the origin of the electrical conduction and magnetic properties. With this aim, scientists from more than ten institutions worldwide, led by the Centre de Recherche Paul Pascal (CNRS/University of Bordeaux), studied the coordination materials MCl2(pyrazine)2 (see Figure). These coordination polymers have the particularity to display a layered (2D) structure and to possess strong metal-ligand interactions, which exacerbate the targeted electronic properties. In this family of iso-structural materials, the scientists’ goal was to understand why the vanadium and titanium analogues are an antiferromagnetic insulator and a paramagnetic metal, respectively, while the chromium-based compound is a ferrimagnetic semiconductor.

By combining the analyses of electrical conductivity, magnetoresistance, magnetic properties, specific heat, and density functional calculations (DFT) with the X-ray absorption spectroscopy carried out at the ESRF’s ID12 beamline, the international research teams managed to get a complete picture of the scientific case. “The ID12 beamline is where all questions regarding local magnetic and orbital moments, oxidation state and electronic structures get answers! And if we cannot get an answer right away, we have the chance to modify the experimental setup on the beamline or to imagine new materials to complete the story. What a luxury to work in this unique world-class facility and with its scientists”, explains Rodolphe Clérac, CNRS researcher at the Centre de Recherche Paul Pascal and main corresponding author of the publication. In this published work, the authors show that in the case of vanadium, the pyrazine ligands simply mediate strong interactions between the V(II) spins that remain localized on each metal centre. On the other hand, for titanium, they highlight the transfer of an electron between the Ti(II) ion and the two pyrazine ligands, during the synthesis. For this reason, TiCl2(pyrazine)2 then displays a metallic behavior (a strongly correlated Fermi liquid state), and even presents the highest electrical conductivity ever observed among coordination solids based on octahedrally coordinated metal ions.

“We have a long-standing collaboration with the research team at the Centre de Recherche Paul Pascal and this work is another example of excellent fundamental science combining their methodology with the unique ESRF’s facilities”, says Andrei Rogalev, scientist in charge of ID12.

This work shows how the choice of the metal ion M in a series of iso-structural materials, allows to finely control their physical properties, and in particular their electrical conduction but also their magnetism. Rodolphe Clérac explains the implications of this finding in the long term: “Our results pave the way for the design of a new generation of metal-organic materials possessing metallic or even potentially superconducting properties”.

Structure of the MCl2(pyrazine)2 materials shown perpendicular (a) and parallel (b) to the 2D layers. Color code: V, dark green; Cl, green; N, blue; C, grey. @K. Pedersen & R. Clérac


Panagiota Perlepe, Itziar Oyarzabal, Laura Voigt, Mariusz Kubus, Daniel N. Woodruff, Sebastian E. Reyes-Lillo, Michael L. Aubrey, Philippe Négrier, Mathieu Rouzières, Fabrice Wilhelm, Andrei Rogalev, Jeffrey B. Neaton, Jeffrey R. Long, Corine Mathonière, Baptiste Vignolle, Kasper S. Pedersenet Rodolphe Clérac

From an antiferromagnetic insulator to a strongly correlated metal in square-lattice MCl2(pyrazine)2 coordination solids

Nature Communications 2022


Rodolphe Clérac, CNRS researcher at the CRPP

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19.07.2022 CNRS Interview: Rodolphe Clérac, 2022 RSC/SCF Lectureship prize in Chemical Sciences from the Royal Society of Chemistry

Find the CNRS interview of Rodolphe Clérac:

Directeur de recherche CNRS au Centre de recherche Paul Pascal (Pessac) et responsable du groupe « Matériaux moléculaires & magnétisme » reçoit le prix « Lectureship in Chemical Sciences » 2022 de la Royal Society of Chemistry, attribué alternativement par la Royal Society of Chemistry et la Société Chimique de France. Cette distinction récompense ses développements de nouveaux domaines de recherche en magnétisme moléculaire et ses contributions originales à l’étude des matériaux magnétiques.

Read more on the CNRS website…

Rodolphe Clérac received the 2022 RSC/SCF Lectureship prize in Chemical Sciences from the Royal Society of Chemistry, for the development of new research areas in molecular magnetism and contributions to the study of magnetic materials.

The Royal Society of Chemistry-Société Chimique de France Lectureship in Chemical Sciences is a reciprocal lectureship awarded alternately by the Royal Society of Chemistry and the Société Chimique de France (SCF), for advances in chemistry made by a scientist while working and residing in France or the UK, respectively.

Dr. Clérac’s team build matter from the atomic level using metals and organic molecules in order to organise them to promote one or several targeted physical properties. This requires a strong synergy between the chemistry and physics of these systems. It is this duality that fascinates Rodolphe Clérac and inspires his research work on molecule-based magnetic materials and molecular magnets. His group’s work offers broad prospects for the preparation of a new generation of lightweight magnetic materials that could be applied within aeronautics, space or mobile technologies and the electronics of tomorrow….

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Our research team is part of ADAGIO, an Advanced Manufacturing Research Fellowship Programme…

ADAGIO is an international fellowship programme aiming at attracting talented post-doc scientists to develop their 3 year projects.

1. Develop your own innovative scientific project
2. Select up to 3-research group
3. Choose one of our partner organization to add industrial skills
4. Submit your application!

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TV7 is talking about coordination chemistry, fundamental sciences and our group!

During more than 7 minutes, this TV report shows the work of our team through different short videos and by interviewing Rodolphe Clérac. The main topics are coordination chemistry, our research work, the CNRS 2021 silver medal, the importance of fundamental research and research funding in France.

Ces pros qui nous inspirent : dans ce rendez-vous hebdomadaire, on découvre les coulisses du monde du travail en Nouvelle-Aquitaine, on comprend les problématiques des entreprises, leurs innovations, et leur agilité dans un monde en pleine mutation.

TV7 : Modes d’Emplois / Chimie de coordination : du temps pour la recherche
Épisode du 17/02/2022

Une première synthèse du nonacène pour des applications en électronique organique

Les acènes sont des molécules linéaires composées de cycles de benzène fusionnés, dont l’extension améliore les performances électroniques, mais complique fortement la synthèse. Des scientifiques du CEMES (CNRS), de l’académie tchèque des sciences (République tchèque) et de l’université d’Hokkaido (Japon) ont obtenu le premier acène stable à neuf cycles benzéniques : le nonacène. Publiés dans la revue Nature Communications, ces travaux pourraient aboutir au développement de nouveaux composants électroniques.

Les acènes sont une famille d’hydrocarbures comprenant plusieurs benzènes fusionnés formant une chaîne linéaire. Ces molécules présentent des propriétés électroniques singulières, car plus ces acènes sont longs et plus leur comportement se rapproche de celui des semi-métaux. Or, comme il s’agit de molécules organiques, les acènes sont beaucoup plus faciles à fonctionnaliser et mettre en forme que les semiconducteurs inorganiques, ce qui permet de leur donner des propriétés supplémentaires et de les déposer sur davantage de surfaces différentes. Les chercheurs tentent donc de concevoir des acènes de plus en plus longs, mais l’ajout de nouveaux cycles benzéniques réduit très fortement la solubilité et la stabilité de la molécule. Si la fabrication du tétracène ou du pentacène, composés respectivement de quatre et cinq cycles de benzène, est bien connue, des doutes subsistaient quant à la possibilité d’aller au-delà de l’heptacène (sept cycles). Des chercheurs du Centre d’élaboration de matériaux et d’études structurales (CEMES, CNRS), de l’académie tchèque des sciences (République tchèque) et de l’université d’Hokkaido (Japon) ont obtenu pour la première fois un nonacène, soit un acène à neuf cycles. Il se présente sous la forme d’un solide noir, qui se conserve sous atmosphère inerte pendant des mois…

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