Marinella Penzo

TYPIX : standardized data and crystal chemical characterization of inorganic structure types

This major reference contains condensed crystal chemical information about individual structure types as well as an extensive section on the crystal chemistry of particular structure families. It clarifies and classifies published data on intermetallic and other inorganic structures.

Explanatory Notes for the Use of the Main Data-Table

The structure types in the Main Data-Table are dassified according to: (1) Increasing space group number. The space group number is included in the page number, and is indicated within parentheses before the Hermann-Mauguin symbol on the first line of each data set (type classification line). (2) Increasing sum of multiplicities of all, fully or partly occupied atom sites in the structure (number of atoms in the unit cell for structures with only fully occupied sites). This number is included in the Pearson code (see Chapter 1.1.), which is indicated at the end of each type classification line. Note that for trigonal structures based on an R Bravais lattice the sum of multiplicities refers to the triple hexagonal cell and that hydrogen atoms in H2O or NH3 molecules, OH- or NH4+ groups, are not considered here. (3) Increasing number of different letters in the Wyckoff sequence. The complete Wyckoff sequence, i.e. the sequence of letters of all, fully or partly occupied atom sites in the standardized structure description, is to be found at the centre of the type classification line. (4) Increasing value of the CG parameter.

Main Data — Table

The labels of the records where the information can be found are given within parentheses; record labels with a trailing asterisk are only present when relevant. A detailed explanation of each record is given in Chapter 5.2.

The Standardization of Crystal Structure Data

The answer to this question must seem evident to any crystallographer who, dealing with inorganic structures, has already wasted time in trying to compare structure data, transformed axes, added shifts, calculated equivalent atom coordinates ..., possibly made errors and had to start the operations over again. In fact, some structures reported in the literature have never been recognized as being identical. This has happened even in Strukturberichte where, for example, the type labels B16 (GeS) and B29 (SnS) correspond to the same atom arrangement.

Crystal Chemical Characterization of Inorganic Structure Types

In this chapter are described some of the general structural relationships which have been observed between inorganic structure types. In the Main Data-Table condensed crystal chemical information about the individual structure types can be found in the “information” records VALEL and DESCR and a limited number of related structure types are mentioned in the RELAT record. It is well known that structures with very different compositions, cell dimensions and/or very different symmetries may show many structural similarities. For example, particular structures can be grouped in a structure series built up of similar elementary building segments, or can be rationalized according to valence electron concentration rules (tetrahedral structures, polyanionic valence compounds, structures with tetrahedral anion complexes etc.). This chapter is intended to give an overview of these relationships through additional comments, references, diagrams, structure drawings etc., presented in more than 50 tables, labelled by a code consisting of a letter and a number. The same codes are reported in the Main Data-Table under the TABLE record (see Chapter 5.2.). In this way, when the reader is interested in a particular structure type, he can get more information on related structures by consulting the crystal chemical tables.

Cross — Reference Tables

Colloquial name of the structure type (LABEL record in the Main Data-Table). Mineral names and colloquial names for salts apply to a single compound. Other names listed here characterize the structure type itself or indicate a structure family to which the structure type belongs.