CsCl octahedron

Figure 2.8 (a) CsCl octahedron with the critical ratio of cation/anion radius of 0.732 (white Cs, gray Cl ) and (b) calculation of the critical ratio of cation/anion radius. With a = 2 and the diagonal equal to 2 r + one gets = v3-1. 

From a geometrical point of view only, this structure could be compared with that of CsCl, with 1 Ca in place of Cs, and the centre of a 6 B octahedron in place of the Cl atom (in the centre of the cell with its axes parallel to the cell axes). Ca is surrounded by 24 B in a regular truncated cube (octahedra and truncated cubes fill space). A number of hexaborides (of Ca, Sr, Ba, Y and several lanthanides and Th, Np, Pu, Am) have been described as pertaining to this structural type. 

It is possible to draw the octahedron on the 8 - ring four times. The structure can be seen as the CsCl - structure with B6 - octahedrons instead of Cl - ions... 

Chlorine. Xenon trioxide reacts with RbCl and CsCl to give compounds with the composition M9(Xe03Cl2)4Cl, which consist of M+ cations, Cl" anions, and infinite chain anions in which each Xe atom is surrounded by a very distorted octahedron of three oxygen atoms (Xe—O 1.77 A) and three Cl atoms (Xe—Cl = 2.96 A). These are the only examples of compounds stable at room temperature that contain Xe—Cl bonds. 

A cluster model used for the calculation of TiFe system is shown in Fig. 17. For simplicity, this is constructed on the basis of the CsCl-type crystal structure of TiFe [49], although the hydrogenation induces a small distortion in the crystal structure. In this model a hydrogen atom is located on the central site of the octahedron consisting of two Fe( 1) atoms and four Ti atoms. In order to examine alloying effects on the hydriding properties, one of the two Fe( 1) atoms is substituted... 

All the alkali metal halides except CsCl, CsBr and Csl form cubic crystals with rock-salt structure, where each metal cation is surrounded by six halide anions, and each anion surrounded by six cations at the comers of an octahedron. See Fig. 5.3. Consultation of a textbook on elementary inorganic or physical chemistry should make it clear that the energy of one mole of the crystalline material relative to the separated, neutral atoms is given by... 

The metal hexaborides MB (with M from group 1-3 or a lanthanide) have a cubic lattice that is similar to that of CsCl (Figure 4.10). All six boron atoms in one octahedron are linked to another octahedron. The distance between the boron atoms within the octahedra is slightly longer than the boron-boron bonds that link the various octahedra. This latter distance changes somewhat with the size of the metal atoms. The hexaborides often have a wide existence range. The value of x in M B can vary between 0.77 and 1 for M = La and between 0.68 and 1 for M = Sm. Most hexaborides are better electrical conductors than the metals themselves and have an... 

The hexaborides of the rare earth elements show interesting properties. RB crystallizes in the CaB structure, where the cations and the B6-octahedrons form a lattice of CsCl-type (fig. 133). In such a lattice two Debye temperatures are observed a low-temperature one (0i 150 K) connected with the soft metal sublattice and a high-temperature one (0 600 K) related to the hard boron sublattice (Paderno... 

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