Topochemical reactions - those in which the composition of a material is modified while its overall structure is left largely intact - are the basis of numerous technologies such as battery electrodes and CO2 capture. This dissertation outlines our efforts to understand the underlying chemical and structural factors controlling the outcome of these reactions. With a focus on the anion sublattice in perovskite-type oxides, this research was performed as part of two projects. First, we explored the use of topochemical oxygen removal reactions for the preparation of new functional materials with potential application in next generation computing. Through this effort, we successfully synthesized the first example of ferromagnetic cubic Sr2FeMoO6 suggesting the possibility of raising the magnetic ordering temperature, and therefore the degree of spin polarization, of this material through topochemical treatments. Second, we investigated the ability to use complex transition metal oxides as oxygen storage materials for new chemical-looping technologies. For example, our studies of La(1-x)Sr(x)FeO(3-d) yielded two primary findings -- cycling reaction kinetics are strongly dependent on Sr content and each sample has an envelope of oxygen storage capacity over a set temperature and atmospheric composition. These projects both used advanced diffraction techniques, neutron and synchrotron X-ray, to study the structure of materials in-situ in order to link their structure to their properties. Furthermore, through this research we developed tools for the rapid refinement of large sets of powder diffraction patterns thus speeding up the rate at which the data from high-speed in-situ diffraction experiments can be analyzed and presented.