Halides, binary structural data

The immense number of chemical compounds formed by the halogens provides chemists with an extraordinary database from which numerous chemical and physical phenomena can be correlated with respect to various periodic trends. From databases like Inorganic Crystal Structure Data (ICSD, http //www.fiz-karlsruhe.de ) and International Centre for Diffraction Data (ICDD, http //www.icdd.com) with 67 000 and 25 000 entries, respectively, one can easily make out that halides are one of the dominant classes of compounds besides oxides. Even within the subset of inorganic solids, there is tremendous diversity of composition, stracture, and properties and to summarize this would create its own encyclopedia. Therefore, the discussion in this article is limited primarily to binary halides, their structures, and some of their properties, except halides of elements which are nonmetals. Binary actinide hahdes are discnssed elsewhere see Actinides Inorganic Coordination Chemistry). Complex hahdes (sohd phases containing two or more kinds of metal ions), ... 

The conditions under which tetrahedra form are becoming clearer, although some of the identifications rely on spectra and a doubt must remain. (How different will be the spectra of [MnCl ] , if and when identified, from that of [MnC f ) The structural data (Tables 32-34) show that, of the binary and ternary compounds, few of the chloro species, more of the bromo species, and most of the iodo species have [MnX4p tetrahedra in the solids. This progression needs no further explanation than size of halide (see especially the Cs and Rb species M2MnX4). In melts, however, M2MnCl4 compounds give tetrahedra. Even in aqueous solution, and in other solvents (Section 41.3.7.3), in the presence of an excess of X , such tetrahedra have been detected, and it is assumed that [MnX, solvent]" tetrahedra also are present. Such latter species are yet poorly... 

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