Crystallographic nomenclature

Crystallographic nomenclature (Bravais lattices, crystal classes, space groups) The following information is generally included in a usual crystallographic description ... 

A report by the International Union of Crystallography Commission on Crystallographic Nomenclature (Lima de Faria et al. 1990) presents a concise description of similar alternative notations, a summary of which is in Table 3.4. 

Figure 9.18 Idealized structures of hydrated didodecyl-phosphatidyl ethanolamine showing some typical bicontinuous cubic phases. (Adapted from Seddon et al, 1990 see this reference for the indicated crystallographic nomenclature.)...

Lima-de-Faria, J., Hellner, E., Liebau, F., Makovicki, E. Parth , E. (1990). Nomenclature of inorganic structure types. Report of the International Union of Crystallography Commission on Crystallographic Nomenclature subcommittee on the nomenclature of inorganic structure types. Acta Cryst. A46,1-11. 

Based on recently obtained crystallographic data, cluster I and II were renamed cluster 2 and 1, respectively. In the following discussion the new nomenclature will be used. 

Twenty-two years later the isolation of the anti-pernicious anemia factor" was announced independently by Smith (5) and Riches (6). Seven years of chemical studies identified 5,6-dimethylbenzimidazole (7), D-ribose (5) and amino-propanol (9) as components of the anti-pemicious anemia factor", but the tetrapyrroline ring structure containing Co(III) awaited the X-ray crystallographic data on the cyano-derivative by Hodgkin and White (10—15). Once the structure of the antipemicious anemia factor was determined it was called Vitamin B12 (cyanocobal-amin). The recommendations of a number of commissions forms the basis of the present system of nomenclature for this molecule and these are presented in Fig. 1. 

A number of points are relevant for a full crystallochemical characterization for each of them a few noteworthy remarks will be presented in the following. To this end, crystallographic conventions, nomenclature and symbols will be used. For a summary of these and of the corresponding definitions the most important reference book is International Tables for Crystallography (Hahn 2002). 

In the previous paragraphs a brief account has been given of the fundamental aspects of the crystallographic description of the structures and structure types of solid phases. A number of symbols and names have been defined and their application to intermetallic compounds exemplified. It must, however, be underlined that both for historical reasons and for the need to improve classification and interpretation of the structural characteristics of intermetallic phases, other symbols and nomenclature criteria have been invented. Some of them have a mathematical basis, others are more colloquial. A selection of these criteria will be given in the following. 

Besides the crystallographic and chemical symbols and nomenclature previously introduced, a few special symbols have been used in this chapter. Generally, for nearly all the metals (Me), a summary is given of their reactivity with the other elements. This is outlined in the text and in figures representing the Periodic Table. In some cases, more than one table is provided for each element. The different binary systems Me-X are identified by the position in the Table of the element X, and their characteristics are briefly described by one of the following symbols inserted in the corresponding box ... 

Nomenclature. The naming of sodium perborate, one of the most important commercial boron compounds, has long been confused. The tetrahydrate has more recently come to be called the hexahydrate. The crystallographically derived names are used to avoid confusion. The commercial or common names are also given. 

IR-11.4.5 Defect clusters and use of quasi-chemical equations IR-11.5 Phase nomenclature IR-11.5.1 Introduction IR-11.5.2 Recommended notation IR-11.6 Non-stoichiometric phases IR-11.6.1 Introduction IR-11.6.2 Modulated structures IR-11.6.3 Crystallographic shear structures IR-11.6.4 Unit cell twinning or chemical twinning IR-11.6.5 Infinitely adaptive structures IR-11.6.6 Intercalation compounds IR-11.7 Polymorphism IR-11.7.1 Introduction IR-11.7.2 Use of crystal systems IR-11.8 Final remarks IR-11.9 References... 

IR-11.6.1 Introduction Several special problems of nomenclature for non-stoichiometric phases have arisen with the improvements in the precision with which their structures can be determined. Thus, there are references to homologous series, non-commensurate and semi-commensurate structures, Vernier structures, crystallographic shear phases, Wadsley defects, chemical twinned phases, infinitely adaptive phases and modulated structures. Many of the phases that fall into these classes have no observable composition ranges although they have complex structures and formulae an example is Mo17047. These phases, despite their complex formulae, are essentially stoichiometric and possession of a complex formula must not be taken as an indication of a non-stoichiometric compound (cf. Section IR-11.1.2). 

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