Structure determination from powder

The Ir complex (NH4)[Ir(NH3)Cl5] has been prepared by the oxidation of the Ir111 analogue with Cl2 at 330 °C, and its structure determined from powder diffraction studies.30... 

David WIF, Shankland K, McCusker LB and Baerlocher Ch, Structure Determination from Powder Diffraction Data, lUCr Monographs on Crystallography 13, Oxford University Press, 2002... 

David, W.I.F., Shankland, K., McCusker, L.B., and Baerlocher, Ch. (2002.) Structure determination from powder diffraction data. Oxford Oxford University Press and lUCr. 

Validation of the Procedures and Results in Structure Determination from Powder XRD... 

Examples of Structure Determination from Powder XRD Data. 158... 

Under such circumstances, the most direct approach for investigating the structural properties of the material of interest is to use powder XRD, although it is important to emphasize that the process of carrying out structure determination from powder XRD data is substantially more challenging than from single-crystal XRD data. There are therefore considerable opportunities for the development of... 

Fig. 2 Schematic diagram showing the sequence of stages involved in crystal structure determination from powder XRD data...

For many molecular materials, crystallization from solution does not yield single crystals of suitable size and quality for single-crystal XRD, and instead produces only microcrystalline powders. In such cases, structure determination from powder XRD data provides a viable route for establishing structural understanding of the resultant materials. 

Certain solid phases, on the other hand, cannot be obtained (even as microcrystalline powders) by crystallization experiments, but instead can be generated only by other types of preparation procedure. Some types of preparation processes commonly (or in some cases inherently) yield microcrystaUine products, including (1) preparation of materials directly from solid-state chemical reactions (see Sect. 6.6), (2) preparation of materials by solid-state desolvation processes (see Sect. 6.4), (3) preparation of materials by solid-state grinding (mechanochemical) processes (see Sect. 6.2), and (4) preparation of materials directly by rapid precipitation from solution (as opposed to crystallization) (see Sect. 6.7). Again, structure determination from powder XRD data may represent the only opportunity for determining the structural properties of new solid phases obtained by such processes. 

Many crystalline solids can undergo chemical transformations induced, for example, by incident radiation or by heat. An important aspect of such solid-state reactions is to understand the structural properties of the product phase obtained directly from the reaction, and in particular to rationalize the relationships between the structural properties of the product and reactant phases. In many cases, however, the product phase is amorphous, but for cases in which the product phase is crystalline, it is usually obtained as a microcrystalline powder that does not contain single crystals of suitable size and quality to allow structure determination by single-crystal XRD. In such cases, there is a clear opportunity to apply structure determination from powder XRD data in order to characterize the structural properties of product phases. 

Structure determination from powder diffraction data W. I. F David, K. Shankland, L. B. McCusker,... 

Refs. [i] West AR (1988) Basic solid state chemistry. Wiley New York, pp 323 [ii] Nazri GA, Pistoia G (eds) (2004) Lithium batteries Science and technology Kluwer, Boston, parts I-III [Hi] David WIF, Shank-land K, McCusker LB, Baerlocher C (eds) (2002) Structure determination from powder diffraction data. Oxford University Press, Oxford, pp 337 [iv] Jenkins R, Snyder RL (1996) Introduction to X-ray powder diffractometry. Wiley, New York, pp 403 [v] Baehtz C, Buhrmester T, Bramnik NN, Nikolowski K, Ehrenberg H (2005) Solid State Ionics 176 1647... 

In addition to structure determination from powder diffraction data as described earlier, another area of considerable current interest is the computational prediction of crystal structures based on energy simulation techniques. In such work, the potential energy, E(r), is computed as a function of the set of variables T that define the structure (the unit cell and space group are usually also included as variables in such calculations), and the E r) hypersurface is searched to find the structure of minimum energy. Representative examples of work in this field may be found in Refs. [74-79], and some work involving the use of evolutionary algorithms to carry out the search procedure has been reported [80-82]. 

As discussed in Sect. 3, the first stage of crystal structure determination from powder diffraction data involves determination of the unit cell by indexing the powder diffraction pattern. Clearly it is not possible to proceed with structure solution unless the correct unit cell has been found at this initial stage. Recognizing this issue, a technique employing a GA for indexing powder diffraction data has been reported [88]. The positions of the peaks in a powder diffraction pattern depend on the unit cell dimensions (lattice parameters) [a, b, c, a, ft, y], and the aim of indexing is to determine the correct lattice parameters from... 

W. 1. F. David, K. Shankland, L. M. McCusker, and Ch. Baerlocher eds, Structure Determination from Powder Diffraction Data , International Union of Crystallography Monographs on Crystallography No 13, lUCr/Oxford University Press, Oxford, 2002. 

AB INITIO STRUCTURE DETERMINATION FROM POWDER DIFFRACTION DATA... 

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