The cubic pores in many Prussian blue analogues are big enough to contain organic cations. In the material (HIm)2K[Fe(CN)6], the imidazolate guest cation is free to rotate in two high-T phases but freezes into position, altering the dielectric constant, at low T. The structural difference between the high-T phases remains controversial. Although the Co analogue has been studied by NMR, the paramagnetic Fe compound cannot be. We thus propose instead to investigate the imidazolate rotation in this material via quasi-elastic neutron scattering. Analysis of the elastic incoherent structure factor as a function of temperature will confirm the number of rotational orientations available to the cation and determine the activation energy for hopping between them. This will resolve the structural controversy and inform the design of new framework materials with targeted dielectric properties.