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A new example appeared at ICIQ, showing that thermal hysteresis still holds in individual molecules in liquid solution. This was a really complex and long path where clearly the expertise and knowledge of a team of three research groups was key to success.

Hysteresis is the tendency of a material to retain one of its properties even after the stimulus that created it disappears. An illustrative case is when iron is exposed to a magnetic field. It will remain magnetized indefinitely until some energy is transferred to the system (a magnetic field in the opposite direction for example). This magnetic memory effect is the basis for recording information on certain types of hard drives.

The advantage of small components that can store information is clear in terms of space and power consumption. Until now, single molecule magnets (SMMs), promising molecular materials that represent the ultimate unit of miniaturization, have been developed. However, they required very low temperatures (–193 ºC) for proper operation, because the magnetic memory effect is quickly lost by thermal activation at the nanoscale.

The occurrence of a memory effect at the level of a single molecule, even upon dilution, was found in a spin cross-linking (SCO) molecule, a polyanionic iron complex. The classical, well-accepted elastic model for SCO systems ruled out the occurrence of molecular bistability, as a memory effect would only be allowed when a bulk crystallographic phase transition occurred. Thus, this discovery shatters previous expectations.

The presence of the memory effect in this polyanion around room temperature was confirmed by several complementary experimental evidences, including magnetic and spectroscopic techniques, both in dilute solid mixtures and in the liquid phase. All of them consistently demonstrated the occurrence of a genuine single-molecule memory effect. These results represent a successful team effort, after almost eight years, by the groups of professors José Ramón Galán-Mascarós, Prof. Mónica H. Pérez-Temprano and Prof. Julio Lloret-Fillol.

“Extraordinary claims require extraordinary evidence, which could only be delivered with a complementary effort from many techniques and multiple backgrounds. ICIQ is leading the way, but we were fortunate to assemble a unique, interdisciplinary team,” says Galán-Mascarós. “Our long NMR experience in elucidating reaction mechanisms in organometallic chemistry was key to investigating this new phenomenon. A very different problem that we could successfully tackle with a fresh mind, looking outside the box,” concludes Prof. Perez-Tembrano.

Computational analysis, led by Professor Eliseo Ruiz (Universitat de Barcelona), identified the origin of this new phenomenon with the appearance of strong intra- and supramolecular interactions, able to slow down the relaxation processes at the single molecule level and thus opening a kinetic thermal hysteresis . Obviously, the previous SCO theory is not refuted, but the appearance of this unexpected molecular property could not be predicted until now.

The discovery of this seemingly impossible slow relaxation process is basic research now, but these results may certainly represent a revolution in the field of spin transition phenomena, as individual SCO molecules open up exclusive opportunities for molecular data storage at technologically relevant temperatures . A new way of storing multifunctional (optical or magnetic) information has emerged and suggests that it is the tip of a large iceberg of new possibilities.

The impossible is the science yet to be discovered and at ICIQ an impossible has come to light.

More information:
Moneo-Corcuera, A., Nieto-Castro, D., Cirera, J., Gómez, V., Sanjosé-Orduna, J., Casadevall, C., Molnár, G., Bousseksou, A., Parella, T. , Martínez-Agudo, JM , Lloret-Fillol, J. , Pérez-Temprano, MH , Ruiz, E. & Galán-Mascarós, JR Molecular memory near room temperature in a polyanionic iron complex . Chem. doi.org/10.1016/j.chempr.2022.09.025

Provided by the Chemical Research Institute of Catalonia