Structural Models of Inorganic Crystals. From the Elements to the Compounds . By Ángel Vegas. Editorial Universitat Politècnica de València. 2018. Hardback, Pp. xxviii+444. Price Euro 99. ISBN 9788490486023

Despite the exponential explosion of the number of research papers dealing with organic and metal–organic compounds (e.g. metal–organic frameworks, polymorphism of organic crystals, crystal engineering, etc.), inorganic crystalline materials continue to attract attention from material scientists, crystallographers, condensed matter physicists, solid state chemists and mineralogists. However, there have been very few books published so far in the XXI century that provide an overview of structural correlations existing between various classes of inorganic compounds based upon the analysis of their structural architecture. The book by Ángel Vegas is a comprehensive (yet provocative and quite original, see below) treatise on crystal chemistry, where the author unifies a large amount of data to construct a coherent conceptual framework for understanding the large family of inorganic structures usually interpreted through the ionic model. The very basic question the author asks is ‘Why do atoms occupy the positions they have in the structures?’, which is given as the title of the Chapter 16. Which factors govern the arrangement of ions in ionic crystals? What is the best way to describe the structure of an inorganic crystal so that correlations to related compounds are immediately seen and understood? The subtitle of the book provides a partial answer: ‘from the elements to the compounds’. In general, the idea that structures of many inorganic oxides, halogenides and chalcogenides can be described as derivatives of parent metals or intermetallides is not new (and the author provides detailed historical notes here and there). However, Vegas wants to demonstrate how these analogies arise from the nature of interatomic interactions in ionic crystals, gathering evidence from different fields of modern research in condensed matter physics, materials and solid state chemistry. The author develops his approach point-by-point in a manner quite accessible to the reader with a primary knowledge of crystallography and inorganic chemistry. The book contains 18 chapters, which are subdivided into 151 subchapters, each with an average length of three book pages. The first three chapters are devoted to the description of the basic concept of crystal chemistry of the compounds that are usually called ‘ionic’. Vegas sharpens his analysis against the ‘ionic model’ that ‘ . . . describes the structures as closestpacked arrays of bulky anions with small cations occupying interstices of that anionic array’ (p. 13). Chapter 4 points out the necessity of alternative approaches, providing some historical examples of structural and geometrical correlations between the cation arrays in the structures of oxides and their parent metals and alloys. This theme is continued in Chapters 6 and 7, where the author comes to the conclusion that ‘oxides are real oxygen-stuffed alloys (my italics) whenever we take into account the high-pressures phases’ (p. 143). We note the rather strange title for subchapter 7.6 ‘Cations are not isolated entities . . . ’, a somewhat incorrect statement, taking into account the range of interactions that cations in oxides are involved in. However, before this conclusion Chapter 5 introduces Zintl phases and the Zintl–Klemm concept with the idea of electron delocalization between metal atoms (e.g. the [Al2] 2 subarray in SrAl2). The author wants us to start to believe that cation–cation interactions in oxides have something in common with metal–metal interactions in Zintl phases. The idea is further promoted in Chapters 8 to 10 that continue to add examples of similarities (or even geometrical identities) of cation arrays in oxides and elemental structures. Therefore, the reader is not surprised ISSN 2052-5206