The title compounds and their deuterides have been prepared by solid-state and solid-gas reactions from the elements and investigated by X-ray and neutron powder diffraction as a function of temperature. At room temperature they crystallize with an anion-deficient cubic K 2 PtCl 6 -type structure (space group Fm3m) in which five hydrogen (deuterium) atoms surround iridium randomly on six octahedral sites with average bond distances of Ir-D=169-171pm. At low temperature they undergo a tetragonal deformation (space group I4/mmm) to the partially ordered Sr 2 IrD 5 (T=4.2K)-type structure in which four hydrogen (deuterium) atoms occupy planar sites with full occupancy (Ir-D=166-170pm) and two hydrogen (deuterium) atoms axial sites (Ir-D=174-181pm) with ~50% occupancy, i.e., the data are consistent with a mixture of square-pyramidal [IrD 5 ] 4 - complexes pointing in two opposite directions. The transitions occur at ~240K (Eu 0 . 5 Ca 1 . 5 IrD 5 , Eu 0 . 5 Sr 1 . 5 IrD 5 ), ~210K (EuSrIrD 5 ), ~200K (EuCaIrD 5 , Eu 2 IrD 5 ), and are presumably of first order.