ABSTRACT
X-ray diffraction (XRD) technique has been used extensively for studying the static aspect of order phenomena and this chapter reviews the most significant results. If one looks at how XRD results have been sometimes presented in literature, he can get the idea that the confusion typical of many studies on hydration even contaminates XRD investigations, as inconsistent results on the same or similar systems are often reported. The chapter quotes most of the diffractometric studies which have come out up to 1985, but only the most reliable results will be priviledged. The state of ions in solution, in fact, has been investigated by XRD in very different situations. The attempt to point out the information directly rising from XRD is implied in the choice of the material. The chapter reviews the mononuclear complex formation between cations and the simplest anions in inorganic aqueous solutions. It presents some comments related to discussion about the modeling technique in presence of complex formation.
