Quasielastic neutron scattering (QENS) has been used to investigate the dynamics of hydrogen in Pr 2 Fe 17 H 4 , where isolated hexagons formed by the interstitial tetrahedral (t) sites of the metal lattice host mobile hydrogen atoms (on average, one H atom per hexagon). An activation energy of 0.10eV has been measured for a localized jump process involving the hopping of these hydrogen atoms among adjacent vertices of each hexagon. This activation energy is somewhat lower compared to that for hydrogen hopping in Pr 2 Fe 17 H 5 , where each hexagon is occupied by two hydrogen atoms. The fraction of the hydrogen atoms immobilized on the t sites by defects in the host metal lattice is slightly higher in Pr 2 Fe 17 H 4 compared to Pr 2 Fe 17 H 5 . These results are consistent with our earlier view of Pr 2 Fe 17 H 5 as a system where the hopping of the t-site hydrogen atoms occurs through the correlated jumps of the two H atoms occupying each isolated hexagon.