Starting from the late seventies, the progressively increased availability of synchrotron light sources has allowed the execution of experiments requiring a high X-ray flux in a continuous interval [1][2][3][4]. Among the various techniques developed, X-ray absorption spectroscopy (XAS, also known as X-ray absorption fine-structure, XAFS) [5][6][7][8][9][10][11][12][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][14][15][16][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], and solid state chemistry [12,[29][30][31].In this chapter, we will provide a brief introduction to the basic theory of XAS spectroscopy (Section 5.2), followed by selected examples having some didactic perspective (Sections 5.3-5.7). 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 CuCl 2 /Al 2 O 3 -based catalysts for ethylene oxychlorination (Section 5.3); the structure, the electronic configuration and the reactivity of Cp 2 Cr molecules encapsulated in porous solids (Section 5.4); the structural characterization of metal complexes in solution (Section 5.5); the structural characterization of the UiO-66 and UiO-67 class of metallorganic frameworks (Section 5.6); and the determination of the local structure of an Alxw Gayw In 1−xw−yw As/Al xb Ga yb In 1−xb −yb As strained heterostructure grown on InP by metallorganic vapor phase epitaxy (Section 5.7) as an example of space-resolved EXAFS applied to a topic pertinent to solid state chemistry.
XAS spectroscopy: Basic backgroundThe aim of this section is to provide the reader with a concise review of the basic physical principles on which the interpretation of EXAFS and XANES data is based. For a more detailed description of the theoretical background and the experimental aspects of XAS we refer to the extensive specialized literature (e.g., [5][6][7][8][9][10][11][12][13]).