The deuterium NMR spectra of the ternary metal deuterides (TMDs) Ca2RhD5 and Ca2IrD5 show that the disorder is dynamic at room temperature, with barriers to the motion of 31.8 and 39.0 kJ mol(-1), respectively. At low temperatures, splittings equivalent to quadrupole coupling constants of 50.9 and 24.5 kHz were obtained for Ca2RhD5 and 68.3 and 41.7 kHz for Ca2IrD5 and are assigned to the planar and apical deuterium positions, respectively. Differential scanning calorimetric study of the transition in Ca2IrH5 located a reversible phase transition at 284 K with an enthalpy change of 650 J mol(-1) and entropy change of 2.3 J K-1 mol(-1).