Caesium crystal structure

A quite new type of antibiotic and one of the few naturally-occurring boron compounds is boromycin (86). Hydrolytic cleavage of D-valine with the M(7) hydroxides gave caesium and rubidium salts of this antibiotic, and crystal structure analysis established the formula as (XIIT). The rubidium ion is irregularly coordinated by eight oxygen atoms. Experiments with models showed that the cation site would be the natural place for the—NH3+ end of the D-valine residue, and the whole structure raises the possibility that transport of larger alkali metals is related to the N-ends of peptides and proteins. 

The caesium thiocyanate complexes of two of the isomers of (XVII) have been isolated (96). For one isomer, (XVIIF), the ratio metal ligand is 1 1 and for another, (XVIIG), it is 1 2. The crystal structure of the 1 1 compound, Fig. 20, shows equal sharing of two thiocyanate ions between the two metals and a somewhat unsymmetrical environment for... 

Figure 8.10 Representation of the crystal structure of [Cs((if-PhMe)3(p-Fln N(SiMe3)2 3)]. ° Indium, caesium, nitrogen and silicon atoms are shown as black spheres, fluorine atoms are grey and carbon atoms are white. Selected bond lengths Inl-NI 2.121(3), lnl-N2 2.128(3), In1-N3 2.127(3), Inl-FI 2.065(2), Cs1-F1 2.777(2)A...

Although the caesium chloride arrangement always occurs when the ratio of radii is approximately unity, the crystal structure observed is not always the one that is expected, and the other alkali... 

Thuery, P., Nierlich, M., Bryan, J. C., Lamare, V., Dozol, J.-F., Asfari, Z., and Vicens, J. . Crown Ether Conformations in 1,3-Calix[4]arene Bis-crown Ethers, Crystal Structures of a Caesium Complex and Solvent Adducts and Molecular Dynamic Simulations, J. Chem. Soc., Dalton Trans. (1997) 4191— 4202. 

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 meet the difficulties presented by metal systems, various wider definitions of chemical combination in terms of crystal structure have been proposed. For example, it has been suggested that we should regard an ideal chemical compound as one in which structurally equivalent positions are occupied by chemically identical atoms, and an ideal solid solution as a structure in which all atoms are structurally equivalent. It is clear that such a definition of chemical combination embraces all the generally accepted compounds, but it is not without objection when applied to metal systems. Thus, to take only one example, the ft phase in the silver-cadmium system already discussed has, in its ordered state, the simple caesium chloride structure and must therefore... 

The crystal structure of caesium triselenocyanate, Cs(SeCN)3, has been determined as monoclinic, space group C2/c, with a = 7.969, fc = 21.156, c = 5.593 A, 3 = 98.84° and Z = 4. The selenium sequence in the triselenocyanate anion is very nearly linear, with ZSeSeSe= 178.31° and Se—Se bond length 2.650 A, which is 0.31 A longer than single covalent Se—Se bonds. The middle selenocyanate group is exactly linear and, within experimental error, the terminal selenocyanate groups are also linear. ... 

Figure 15 X-Ray crystal structure of the caesium picrate complex of 17.

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