Chemistry crystal-structure analysis

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. 

Dorset, D. L. and Moss, B., Electron crystal structure analysis of linear polymers - an appraisal, in Polymer Characterization, Carver, C. D. (Ed.), Advances in Chemistry Series, Vol. 203, American Chemical Society, Washington, DC, 1983, 409-416. 

A feature of these acidic antibiotics is that their chemical constitutions were established by crystal structure analysis, having defied classical organic chemistry, even aided by spectroscopic techniques. The reason for this is apparent from the formulae, (X)—(XII), examples chosen because the heavy atom salts are isomorphous with those of alkali metals. The formulae show the correct absolute configurations as determined by X-ray methods. 

Jeffrey, G. A., and Rosenstein, R. D., Crystal-structure Analysis in Carbohydrate Chemistry, 19, 7-22... 

He first graduated, in 1928, at the University of Sheffield, where he became a lecturer in chemistry, with research interests chiefly in the electrochemical field. In 1946 he moved to J. M. Robertson s laboratory at Glasgow, and his interests then began to turn towards crystal-structure analysis by x-rays and neutrons. He has applied Robertson s methods mainly to the study of hydrogen-bonded crystals and his preoccupation with this topic continues. 

Several interesting mechanistic features of silicon chemistry have been found. Attempts to eliminate LiF led to dimerization in a head to tail (2 + 2) cycloaddition or rearrangement of the formed iminosilene.19 The limits of dimerization are reached with the dimer diisopropyl-(tri-tert-butylphenylimino)silene, for which the crystal structure analysis shows severe steric distortions.20... 

Although tetrahedral transition metal complexes are familiar in coordination chemistry, only two tetrahedral complexes have been studied by accurate X-ray crystal structure analysis Co046- in CoAl204 (84) and Cr042- in a-K2Cr04 (85). 

The binding of ammonium ion, NH4+, by 18-crown-6 was demonstrated early in the history of macrocycle chemistry. The O-H-N in crowns or N-H-N interaction in azacrowns has been characterized by a variety of techniques, including NMR, calorimetry, and X-ray crystal structure analysis. Recent studies in this area have shown that both quaternary and secondary ammonium salts can form complexes with crowns. In the latter case, a rotaxane molecule was prepared by treatment of a dibenzylammonium salt with dibenzo-24-crown-8 and other macrocycles, including pyrido-24-crown-8. The solid-state structure of the pseudo-rotaxane structure obtained with pyrido-24-crown-8 is shown in the left panel of Figure 23. 

Preliminary three-dimensional atomic coordinates of atoms in crystal structures are usually derived from electron-density maps by fitting atoms to individual peaks in the map. The chemically reasonable arrangement of atoms so obtained is, however, not very precise. The observed structure amplitudes and their relative phase angles, needed to calculate the electron-density map, each contain errors and these may cause a misinterpretation of the computed electron-density map. Even with the best electron-density maps, the precisions of the atomic coordinates of a preliminary structure are likely to be no better than several hundredths of an A. In order to understand the chemistry one needs to know the atomic positions more precisely so that better values of bond lengths and bond angles will be available. The process of obtaining atomic parameters that are more precise than those obtained from an initial model, referred to as refinement of the crystal structure, is an essential part of any crystal structure analysis. 

We have written this book with two main purposes in mind. One aim is to acquaint chemists and biochemists with the general principles of crystal structure analysis so that they can critically appraise articles in the crystallographic literature, and extract, with a reasonable comprehension of the precision of the results of the experiment, any structural information they are interested in. The second aim is to make the reader aware of the vast amount of structural information that has resulted from this method of analysis, to inform him or her of how to access the results in the most useful way, and to indicate the manner by which these types of data have enhanced our understanding of chemistry and biochemistry. It is our aim to place the method in context with other methods of structure analysis, such as solution studies (nuclear magnetic resonance and infrared analyses) and molecular modelling. 

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