Reaction between Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> and CaH<sub>2</sub> or LiH yields the iridium-containing oxyhydride phases Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3.25</sub>H<sub>0.75</sub> or Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>2.66</sub>H<sub>1.33</sub>, respectively. Analysis of Mn K-edge XANES data indicate the presence of Ir<sup>3+</sup> centers in these oxyhydride phases, whose low-spin d<sup>6</sup> configuration is consistent with the "covalent stabilization" of the metastable oxyhydride phases, as seen previously in analogous ruthenium and rhodium containing materials. Neutron powder diffraction data indicate the hydride ions are located exclusively within the "equatorial" anion sites of Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3.25</sub>H<sub>0.75</sub>. In contrast, hydride ions are observed on both the equatorial and axial anion sites of Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>2.66</sub>H<sub>1.33</sub>. This highly unusual anion distribution is attributed to a combination of the strong <i>trans</i>-influence of Ir-H σ-bonds and the stabilization of <i>fac</i>-IrO<sub>3</sub>H<sub>3</sub> centers by spin-orbit coupling effects. Magnetization data indicate that Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> and Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3.25</sub>H<sub>0.75</sub> adopt spin glass states at low temperature, behavior which is attributable to the cation disorder in Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> and the cation and anion disorder in Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3.25</sub>H<sub>0.75</sub>. In contrast, magnetization data collected from Sr<sub>2</sub>Mn<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>2.66</sub>H<sub>1.33</sub> show no evidence of any magnetic phase transition down to 5 K, consistent with the dilution of the magnetic network by the introduction of diamagnetic Ir<sup>3+</sup> on the formation of the oxyhydride phase.
