Spatiotemporal Studies of Soluble Inorganic Nanostructures with X-rays and Neutrons

This review addresses the use of X-ray and neutron scattering and X-ray absorption to describe how inorganic nano-structured materials assemble, evolve, and function in solution. We first provide an overview of techniques and instrumentation (both large user facilities and benchtop). We review recent studies of soluble inorganic nanostructure assembly, covering the disciplines of materials synthesis, processes in nature, nuclear materials, and the widely applicable fundamental processes of hydrophobic interactions and ion-pairing. Reviewed studies cover size regimes and length scales ranging from sub-angstrom (coordination chemistry and ion-pairing) to several nanometers (molecular clusters; i.e. polyoxometalates, polyoxocations and metal-organic polyhedra), to meso-scale (supramolecular assembly processes). Reviewed studies predominantly exploit 1) SAXS/SWAXS/SANS (small and wide angle X-ray or neutron scattering), 2) PDF (pair distribution function analysis of X-ray total scattering), and 3) XANES and EXAFS (respectively X-ray absorption near edge structure and extended X-ray absorption fine structure). While the scattering techniques provide structural information, X-ray absorption yields oxidation state, in addition to local coordination. Our goal for this review is to provide information and inspiration for the inorganic/materials science communities that may benefit from elucidating the role of solution speciation in natural and synthetic processes.