  Enhanced coupling of material properties offers new fundamental insights and
routes to multifunctional devices. In this context 5d oxides provide new
paradigms of cooperative interactions driving novel emergent behavior. This is
exemplified in 5d osmates that host a metal-insulator transition (MIT) driven
by magnetic order. Here we consider the most robust case, the 5d perovskite
NaOsO3, and reveal a giant coupling between spin and phonon through a frequency
shift of {\Delta}{\omega}=40 cm-1, the largest measured in any material. We
identify the dominant octahedral breathing mode and show isosymmetry with spin
ordering which induces dynamic charge disproportionation that sheds new light
on the MIT. The occurrence of the dramatic spin-phonon-electronic coupling in
NaOsO3 is due to a property common to all 5d materials: the large spatial
extent of the 5d ion. This allows magnetism to couple to phonons on an
unprecedented scale and consequently offers multiple new routes to enhanced
coupled phenomena.
