However, this simplified defect reaction only provides a partial description of the structure of these defective materials. Bulk chemical analysis indicates that in addition to B site vacancies 'hollow' perovskites contain a substantial concentration of iodide vacancies, as much as 6%, and diffraction measurements indicate the presence of local defect-ordering beyond that visible in the average structure. This example illustrates the general propensity for defective hybrid materials to contain both a wide diversity of point defects and for correlated defect disorder to emerge from the interactions between defects. These two trends are just as important for the Prussian Blue analogue (PBA) family of cyanide frameworks. In Prussian Blue itself, the substitution of Fe 2+ for Fe 3+ is compensated by the formation of Fe(CN) vacancies: