Lena Scherthan, Rouven F. Pfleger, Hendrik Auerbach, Tim Hochdörffer, Juliusz A. Wolny, Wenli Bi, Jiyong Zhao, Michael Y. Hu, Esen Ercan Alp, Christopher E. Anson, Rolf Diller, Annie K. Powell, Volker Schünemann

• Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) using the Mössbauer isotope 161Dy has been employed for the first time to study the vibrational properties of a single-molecule magnet (SMM) incorporating DyIII, namely [Dy(Cy3PO)2(H2O)5]Br3⋅2 (Cy3PO)⋅2 H2O ⋅2 EtOH. The experimental partial phonon density of states (pDOS), which includes all vibrational modes involving a displacement of the DyIII ion, was reproduced by means of simulations using density functional theory (DFT), enabling the assignment of all intramolecular vibrational modes. This study proves that 161Dy NRVS is a powerful experimental tool with significant potential to help to clarify the role of phonons in SMMs.