Small Angle X-ray Scattering of Group V Polyoxometalates

Small and wide-angle X-ray scattering (SWAXS) is a useful technique for probing the size, shape, reactivity, and interactions of dissolved species. It has been used extensively to characterize dissolved biomolecules, polymers, quantum dots, and nanoparticles. Polyoxometalates (POMs) are ideal for solution characterization via X-ray scattering because they are absolutely discrete in size, and the high-Z metal cations provide excellent scattering contrast. In this review, we discuss the use of SWAXS in aqueous metal-oxo chemistry: reviewing older work and summarizing our most recent published work. These recent studies include classic POMs of Group V and Group VI, as well as metal-oxo clusters outside of early d 0 transition metals and are described briefly as follows: 1) direct observation of linking dodecaniobate Keggin ions into chains, 2) characterizing prenucleation Hf-sulfate clusters, 3) understanding the effect of protonation and ion-association of hexaniobate on its base-hydrolysis reactivity, 4) alkaliPOM association of niobate, tantalate, niobotungates, and tantalotungstate Lindqvist ions, and 5) the effect of protonation of Lindqvist ions on solution behavior.