We propose to measure powder neutron diffraction data from some new iridium oxides prepared using mild hydrothermal reaction conditions. Although we have some structural models from laboratory powder X-ray diffraction data that suggest the identity of these mixed-metal oxides phases, neutron diffraction is crucial to refine the structures in order to provide details of the oxide ion location, content and the details of metal-site vacancies. The materials are being studied for the solid-state redox properties so it is vital that we have accurate structural models. This work forms part of a wider programme that is investigating how the use of solution crystallisation allows the controlled formation of complex metal oxide phases: structure refinement of these phases is needed to allow the effect of reaction conditions on the outcome of atomic order to be established.