Crystallographic position General

Many of the nitrosyls studied are 5-coordinate, and analysis of crystallographic results indicates that, in general, in the trigonal bipyramid structures NO is found in the equatorial position in a linear geometry whereas in a square pyramidal structure, there is a bent M—N—O linkage in an apical position. A further point of interest is that in compounds like Ir(NO)Cl2(PPh3)2, the nitrosyl group bends in the more hindered (P—Ir—P) plane. 

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 ... 

The surfaces that form subunit-subunit contacts are very much like parts of a protein interior detailed fit of generally hydrophobic side chains, occasional charge pairing, and both side chain and backbone hydrogen bonds. Twofold symmetry is the most common relationship between subunits. The 2-fold is often exact and can be part of the actual crystallographic symmetry, as for the prealbumin dimer in Fig. 62. However, in many cases (e.g., Tulinsky et al., 1973 Blundell et al., 1972) individual side chains very close to the approximate 2-fold axis must take up nonequivalent positions in order to avoid overlapping (see Fig. 63). Conformational nonequivalence can extend further away from the axis and produce such effects as different... 

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