The advent of accelerator-driven x-ray free-electron lasers has opened new avenues for high resolution structure determination via diffraction methods that go far beyond conventional x-ray crystallography methods. While these techniques rely on coherent scattering, incoherent processes like Compton scattering and fluorescence emission - the predominant scattering mechanism in the x-ray regime - are generally considered detrimental for imaging applications. Here we show that exploiting intensity correlations of incoherent x-ray fluorescence radiation allows one to image the full 3D structure of the fluorescing atoms with at least double the resolution of conventional crystallography measurements. We will study the application of this approach to image transition metal clusters in biologically relevant molecules like nitrogenases and dehydrogenases. Once successful, this method would eventually reveal hitherto unknown reaction steps in photosynthesis or nitrogen fixation that go along with subtle changes of the metal-cluster structure. The high-resolution determination of the metal atom positions will also assist phasing methods in macromolecular crystallography similar to anomalous dispersion methods. Incoherent diffractive imaging via fluorescence detection bears a number of properties that are conceptually superior to those of coherent methods
