had not yet been formulated explicitly. New in this work is also that we actually observe transitions to this excited state spectroscopically, allowing the precise determination of its energy. Secondly, we have shown that the magnetic coupling in the radical bridged complex is extremely strong, and have directly observed transitions to spin-excited states. This finding shows that in this compound, spin-excited states are located at such high energies that they do not act as intermediate states in the Orbach mechanism of magnetic relaxation. These results underline the viability of using radical-bridged polynuclear transition metal complexes as a strategy to improve single-molecule magnet properties, such as slow relaxation of the magnetic moment. Thirdly, our investigations reveal that the magnetic-field-dependent features found in experiment are largely due to vibrational transitions that are perturbed by coupling to the spin system, rather than being due to magnetic resonance transitions. Thus, we demonstrate conclusively the importance of spin-phonon coupling for the observation of these features. Spin-phonon coupling is also at the heart of magnetic relaxation, but the majority of research in this area has so far been theoretical. Our theoretical efforts revealed that especially the off-diagonal elements D Previous researches have mainly focussed on the D (a) and E (a) elements. Hence, this work now adds substantial insight into this phenomenon. To move forward in terms of magnetic bistability, it appears imperative to increase the number of strongly exchange coupled ions beyond two, while keeping the single-ion ZFS tensors parallel.