Structural and electronic characterization of nano-sized inorganic materials by X-ray Absorption Spectroscopies

Starting from the late seventies, the progressively increased availability of synchrotron light sources allowed the execution of experiments requiring a high X-ray flux in a continuous interval [1-4]. Among the various techniques developed, X-ray absorption spectroscopy (XAS, also known as X-ray absorption fine-structure, XAFS) [5-13] in both near (XANES) and post (EXAFS) edge regions, has become a powerful characterization technique widely employed in many research fields concerning inorganic chemistry, such as catalysis [13-17], organometallic and coordination complexes [18], metal nanoparticles [19,20], electrochemical processes [21,22], coordination polymers or metallorganic frameworks [23], bio-inorganic molecules including metalloproteins [24-27], chemistry of actinide elements [28], solid state chemistry [12,29-31]. In this chapter, we will provide a brief introduction to the basic theory of XAS spectroscopy (Section 2), followed by selected examples having some didactic perspective (Sections 3-7). For the sake of brevity, only a fraction of the subjects mentioned above will be discussed; in particular, the chapter will deal with: the reactivity of the CuCl2/Al2O3-based catalysts for ethylene oxychlorination (Section 3); the structure, the electronic configuration and the reactivity of Cp2Cr molecules encapsulated in porous solids (Section 4); the structural characterization of metal complexes in solution (Section 5); the structural characterization of the UiO-66 and UiO-667 class of metallorganic frameworks (Section 6); and the determination of the local structure of an AlxwGaywIn1-xw-ywAs/AlxbGaybIn1-xb-ybAs strained heterostructure grown on InP by metallorganic vapour phase epitaxy (Section 7) as an example of space resolved EXAFS applied to a topic pertinent to solid state chemistry.