CsCl Crystalline Structure

Figure 4. The quasi-cubic units of crystalline network for 1,3,5,7- tetrahydroxyadamantane. Molecules are shown as spheres and hydrogen bonds as solid linking hnes. This crystalline structure is similar to that of CsCl. Taken from Ref. [8] with permission.

The reader should be cautioned that the radius rules above are by no means absolute and in fact are only obeyed 50% of the time. More ionic compoimds have the rock salt (NaCl) structure and fewer have the CsCl structure than would be predicted from the cation/anion radius. StiU, the use of the radius ratio is a good place to start in trying to imderstand the crystalline structure of binary ionically bonded compoimds. 

The crystalline structure of 1,3,5,7-tetracarboxy adamantane is formed via carboxyl hydrogen bonds of each molecule with four tetrahedral nearest neighbors. The similar structure in 1,3,5,7-tetraiodoadamantane crystal would be formed by I... I interactions. In 1,3,5,7-tetrahydroxyadamantane, the hydrogen bonds of hydroxyl groups produce a crystalline structure similar to inorganic compounds, such as a CsCl, lattice [19] (see Figure 3.4). 

Figure 1.7 The structures of crystalline sodium chloride (NaCI), cesium chloride (CsCl), and zinc sulfide (ZnS).

Evaluation of intensities of X-ray diffraction patterns indicates that the CsCl structure is well ordered in crystalline CsAu. Excess Cs, which is the primary source for conduction electrons, is dispersed in the lattice with increase of the cell parameter (105). Cesium-133 NMR measurements (line shapes, Knight shifts, and relaxation times) confirm this result (105). The interpretation of the data for RbAu is less straightforward, however. 

Fig. 1.20 The B2-type CsCl structure of FeTi stoichiometric, ordered, compound (left), and room-temperature hydrogen PCT properties for B2-type FeTi hydrogen storage alloys amorphous - a, nanocrystalline - b, and crystalline - c (adopted from [155])...

At ambient conditions, the crystalline alkali halides CsCl, CsBr, and Csl have the Csl structures whereas all others adopt the rocksalt structure (see Alkali Metals Organometallic Chemistry)-, see Figure 1. 

All the alkali metal halides except the cliloride, bromide and iodide of caesium form cubic crystals with the rock salt lattice and show a co-ordination number of 6. The exceptions are also cubic, but have the caesium chloride structure (Fig. 133) characterised by a co-ordination number of 8. The radius ratio for CsCl, Cs /Cl" = 0.93, allows 8 co-ordination, but is so near the ratio for 6 co-ordination that caesium chloride is dimorphous, changing, at 445°, from the caesium chloride to the rock salt structure. The crystalline halides are generally markedly ionic, though, as expected, lithium iodide is somewhat covalent, for iodide is the largest and most easily polarised simple anion and lithium, the smallest alkali metal cation, possesses the strongest polarising power. 

To specify the complete structure of a crystalline solid it is only necessary to show one unit cell, but interpreting these pictures requires practice. Figure 1 shows some views of the cesium chloride structure (CsCl, depicted as MX). 

BM) and are believed to possess a trans octahedral structure (49). The corresponding reactions of ReCl4(NCMe)2 with methanol and ethanol give the green crystalline complexes ReCl4[NH=C(Me)OR]2 (M = Me or Et) (50) in the case of the methanol reaction, Cs2[Re(0-Me)Cl5] (Section 43.6.1.9) can be isolated from the reaction filtrate upon addition of CsCl. 

Surprisingly, many cubic metals behave in a similar fashion, although the effect has been masked by the fact that the mechanical properties are most often measured on poly crystalline solids. For example, the commonplace metallic alloy /3-brass, CuZn, which has the CsCl structure, is noticeably auxetic. A tensile stress applied along the [001] direction... 

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... 

Crystalline CsCl, CsBr and Csl all adopt so-called CsCl structures in which each cation is surrounded by eight anion and each anion is surrounded by eight cations. The Madelung constants are M = 1.763. Calculations similar to those that we have outlined for the rock-salt structure indicate that the bond distances in the crystals should be 18% longer than in the gas phase. The observed elongations decrease from 22% in CsCl to 19% in Csl. 

Unit cells of crystalline NaCl and CsCl are pictured in Figures 12-48 and 12-49, respectively. We can investigate these structures for their consistency with the formula of the compound and the type of hole the cation occupies. 

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