Molecular magnets encompass a diverse family of systems displaying phenomena ranging from slow magnetic relaxation and molecular‑scale hysteresis to exceptionally long spin‑coherence times relevant for quantum information applications. While synthetic chemistry has enabled precise control over their magnetic properties, it is increasingly clear that these properties are fundamentally influenced, and often limited, by spin–phonon coupling. Vibrational modes provide pathways for the dissipation of magnetic energy, and in crystalline materials the relevant low‑energy modes include acoustic phonons, which propagate through the lattice and therefore cannot be understood solely at the single‑molecule level. Gaining a detailed understanding of these vibrations, and of how they couple to molecular spins, is essential for developing functional molecular magnetic devices and for achieving rational control over decoherence mechanisms.
Inelastic neutron scattering (INS) offers a powerful means of probing vibrational and magnetic excitations simultaneously. Unlike optical spectroscopies, vibrational spectroscopy with INS is free from selection rules, allowing access to the full vibrational spectrum, and its intrinsic sensitivity to momentum transfer enables the direct observation of acoustic phonons, which are otherwise difficult or impossible to measure.
In this contribution, I will present INS analyses across a series of molecular magnets, highlighting how acoustic phonons manifest in their spectra and how these vibrational features relate to molecular structure and intermolecular interactions. I will discuss how such insights into low‑energy vibrational dynamics and spin–phonon coupling can inform the design principles for next‑generation molecular magnetic and quantum devices.