Crystal structures complex compounds

The complexity of many of these molecules contributes to errors in assignment of their structure. The crystal structure of an inhibitor of starfish embryonic development led to a revision of its structural assignment. Instead of a 4-oxo compound, the correct structure is 4-amino-7-(/ -D-ribofuranosyl)-3//-furo[3,2-d]pyrimidine <92Ml 707-02). The crystal structure of compound (5), an intermediate in the enantioselective synthesis of 8-epicastanospermine has also been reported <93AX(C)40). 

D. E. Palin and H. M. Powell. J. Chem. Soc. 1947, 208-21. Crystal structure complexes of hydroquinone-(small, volatile compounds). 

Interpretation of interatomic vectors. Use of known atomic positions for an initial trial structure (a preliminary postulated model of the atomic structure) can be made, by application of Equations 6.21,4 and 6.21.5 (Chapter 6), to give calculated phase angles. Methods for obtaining such a trial structure include Patterson and heavy-atom methods. Such methods are particularly useful for determining the crystal structures of compounds that contain heavy atoms (e.g., metal complexes) or that have considerable symmetry (e.g., large aromatic molecules in which the molecular formula includes a series of fused hexagons). The Patterson map also contains information on the orientation of molecules, and this may also aid in the derivation of a trial structure. 

Taylor, M. R., Gabe, E. J., Glusker, J. P., Minkin, J. A., and Patterson, A. L. The crystal structures of compounds with antitumor activity. 2-Keto-3-ethoxybutyraldehyde bis(thiosemicarbazone) and its cupric complex. J. Amer. Chem. Soc. 88, 1845-1846 (1966). 

Also soon after the first crystal structure of ER, more traditional structure-based design work started to appear. The group of Stauffer et al. [113] used an acyclic amide structural template combined with the ER crystal structure to find additional hydrogen bonds and increase affinity. A number of separate groups, with just a few mentioned here [114-116], have utilized the crystal structure complexes to generate receptor-based alignment for a series of compounds, which were in turn used to generate predictive 3D-QSAR models. 

This concludes our discussion of some of the general principles underlying the internal architecture of crystals. As we have seen, it has been possible to illustrate these principles in terms of the relatively simple structures so far described. We now proceed to consider the crystal structures of compounds of greater chemical complexity. Such structures do, of course, display a number of features not hitherto encountered, but we shall find that these features can for the most part be interpreted in terms of the general principles already discussed, and that few further such principles will have to be invoked. 

Interest has centred almost exclusively on square-planar complexes of palladium(ii) and platinum(ii), and a number of topics have attracted particular attention. The structural /ron -influence has been frequently discussed in platinum(ii) complexes the effect is now rather well documented, and comparative data on palladium(ii) compounds are beginning to accumulate. The kinetic and thermodynamic effects of intramolecular overcrowding, a popular subject in the 1950 s, are again beginning to interest co-ordination chemists and have motivated a number of structural studies. Several papers have been concerned with chelate complexes involving S-donor ligands. A review of crystal structures of compounds of the platinum-group metals has appeared. ... 

The examples, discussed above, show that ternary compounds which are in equilibrium with each other are related with respect to their crystal structure. These compounds contain at least one mutual fi agment or atomic cluster. Sometimes they form homologous series of structures. This fact can be used for the investigation of compounds with unknown crystal structure. However, to date there are a number of powerful program packages available for the determination of crystal structures by direct methods. However, the application of direct methods for structure determination using powder X-ray data is sometimes not successful, especially for complex structures. In such cases the knowledge of structure relations between compounds which are in equilibria becomes very useful if the structures of some of them are known. 

Syntheses, crystallization, structural identification, and chemical characterization of high nuclearity clusters can be exceedingly difficult. Usually, several different clusters are formed in any given synthetic procedure, and each compound must be extracted and identified. The problem may be compounded by the instabiUty of a particular molecule. In 1962 the stmcture of the first high nuclearity carbide complex formulated as Fe (CO) C [11087-47-1] was characterized (40,41) see stmcture (12). This complex was originally prepared in an extremely low yield of 0.5%. This molecule was the first carbide complex isolated and became the foremnner of a whole family of carbide complexes of square pyramidal stmcture and a total of 74-valence electrons (see also Carbides, survey). 

In spite of the slow development of crystal structure analysis, once it did take olT it involved a huge number of investigators tens of thousands of crystal structures were determined, and as experimental and interpretational techniques became more sophisticated, the technique was extended to extremely complex biological molecules. The most notable early achievement was the structure analysis, in 1949, of crystalline penicillin by Dorothy Crowfoot-Hodgkin and Charles Bunn this analysis achieved something that traditional chemical examination had not been able to do. By this time, the crystal structure, and crystal chemistry, of a huge variety of inorganic compounds had been established, and that was most certainly a prerequisite for the creation of modern materials science. 

Crystal structure, crystal defects and chemical reactions. Most chemical reactions of interest to materials scientists involve at least one reactant in the solid state examples inelude surfaee oxidation, internal oxidation, the photographie process, electrochemieal reaetions in the solid state. All of these are critieally dependent on crystal defects, point defects in particular, and the thermodynamics of these point defeets, especially in ionic compounds, are far more complex than they are in single-component metals. I have spaee only for a superficial overview. 

The materials shown and described above were generally prepared from the nucleophilic phenoxide or alkoxide and the appropriate bromide. The syntheses of a variety of such compounds were detailed in a report which appeared in 1977. In the same report, complex stability and complexation kinetics are reported. Other, detailed studies, of a similar nature have recently appeared" . Vogtle and his collaborators have also demonstrated that solid complexes can be formed even from simple polyethylene glycol ethers . Crystal structures of such species are also available... 

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