Molecular Magnetism : the attractive legacy of Olivier Kahn
Résumé
In 1992, Olivier Kahn (France, 1942–1999) defined the research field of molecular magnetism in the preface of his pioneering book1 as follows: “Molecular magnetism deals with the magnetic properties of isolated molecules and assemblies of molecules. These molecules may contain one or more magnetic centers. Assemblies of molecules are most often found in molecular crystals with very weak interactions between the molecular entities. They can be found in extended systems, built from molecular precursors or “bricks”, in a way that maximizes the interactions between the bricks and, hopefully, yields bulk magnetic properties.” In that pedagogic textbook, Olivier Kahn remarkably set up some intuitive concepts for rationalizing the exchange interaction between transition metals, and how to elaborate and assemble appropriate molecular building blocks to direct the desired magnetic interactions. An efficient methodology was thus offered to synthetic chemists. Since then, molecular magnetism has continuously attracted chemists to judiciously design new molecule‐based architectures, physicists for advanced characterizations of the properties of these new compounds, and theoreticians to understand and predict their fascinating behavior. This research field is intrinsically multidisciplinary, at the interface of molecular and solid‐state sciences, with strong potential to be at the forefront of future technological innovative applications.
In the 1970s, Olivier Kahn foresaw the interest of molecular magnetism, both from the fundamental and applicative points of view. In that sense, he rationalized and simplified the concept of magnetic orbitals to predict and design the desired exchange interaction between magnetic centers. His approach has been used successfully to promote room temperature molecule‐based magnets. He also strongly emphasized the possible magnetic and optical bistability of materials built from spin‐crossover molecules that he used to describe as “Doctor Jekyll and Mister Hyde”.2 He went one step further toward applications and implemented spin‐crossover molecules in the first electronic device with the Philips research laboratory.3 By combining his incredible pedagogical talent, his communicative passion for sciences with the visionary nature of his ideas, he was at the source of many scientific breakthroughs in his laboratory but also inspired numerous research groups worldwide.
This thematic issue pays tribute to Olivier Kahn, showing the richness of the scientific developments in molecular magnetism in France and worldwide since he passed away at the end of 1999. This community is strongly active with regular annual meetings (International Conference on Molecule‐based Magnets – ICMM, and European Conference on Molecular Magnetism – ECMM) and federative with European (MAGMANet,4 COST MolSpin5) and French (GdR MCM26) networks. Widely multidisciplinary, this issue covers recent progress in the engineering of molecular magnets (from isolated molecules to nanoparticles and tunable supramolecular networks), switchable magnetic molecules (spin crossover, electron transfer, etc.) and multifunctional materials (purely molecular or hybrid systems). These advances are supported by instrumental developments in time‐resolved optical or X‐ray characterizations, nanoscale studies, multistimuli (pressure, light, temperature, fields) manipulations, theoretical calculations, and modeling. Some of the chemically designed systems are also integrative components of smart devices such as magnetic resonance imaging, molecular electronics and spintronics, smart pigments, and so on.
In this special issue, the essay by Verdaguer and Gatteschi nicely reminds the seminal history of molecular magnetism. The three Microreviews by Journaux, Mathonière, Bleuzen, and co‐authors, in addition to several other papers, put into perspective the pivotal role played by chemistry in this research field to design bistable molecular units, nanoparticles, or extended networks, a scientific approach at the heart of Olivier Kahn's work. All the developments in single‐molecule magnets,7 single‐chain magnets,8 and molecular electronics9 benefit from the recent improvement in physical characterizations such as ultrafast spectroscopy and X‐ray diffraction/spectroscopy, paramagnetic NMR spectroscopy, neutron or synchrotron radiation facilities, and all the developments of imaging at small scales (AFM, STM, ...). The increasing interactions between chemists and physicists are reinforced by the contribution of theoreticians to understand and predict the behavior of these molecule‐based magnetic materials. This is particularly important, as illustrated in this issue, in the development of multifunctional materials in which luminescence or nonlinear optical properties are observed, or in molecular electronics where switchable molecules are associated to functional substrates.
Molecular magnetism is an extremely active research field, gathering more and more researchers, especially because the envisioned applications are getting closer and closer to being realized. This issue is a snapshot of the developments made over the last years, and we hope the readers will catch the permanent effervescence of this scientific community. We wish to thank all contributors, reviewers, and the EurJIC editorial team for their high‐quality and professional work.