Organic crystal structures

Organic solids have received much attention in the last 10 to 15 years especially because of possible technological applications. Typically important aspects of these solids are superconductivity (of quasi one-dimensional materials), photoconducting properties in relation to commercial photocopying processes and photochemical transformations in the solid state. In organic solids formed by nonpolar molecules, cohesion in the solid state is mainly due to van der Waals forces. Because of the relatively weak nature of the cohesive forces, organic crystals as a class are soft and low melting. Nonpolar aliphatic hydrocarbons tend to crystallize in approximately close-packed structures because of the nondirectional character of van der Waals forces. Methane above 22 K, for example, crystallizes in a cubic close-packed structure where the molecules exhibit considerable rotation. The intermolecular C—C distance is 4.1 A, similar to the van der Waals bonds present in krypton (3.82 A) and xenon (4.0 A). Such close-packed structures are not found in molecular crystals of polar molecules. 

With nonpolar aromatic molecules such as benzene, naphthalene and anthracene, cohesion is almost entirely due to van der Waals interaction, but the cohesive energies are significantly larger than in aliphatic nonpolar molecules. The larger cohesive energies arise from the greater polarizability of the n-clouds. Arrangement of molecules 

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Gavezzotti A and G Filippini 1996. Computer Prediction of Organic Crystal Structures Using Partial X-ray Diffraction Data, journal of the American Chemical Society 118 7153-7157. 

Price SSL, Price LS (2005) Modelling Intermolecular Forces for Organic Crystal Structure Prediction 115 81-123... 

R. S. Rowland, R. Taylor, Intermolecular nonbonded contact distances in organic crystal structures. J. Chem. Phys. 100 (1996) 7384. 

It is not our aim to provide here a comprehensive review of solid-state organic chemistry. We intend rather to dwell on the interplay between stereochemical factors and solid-state effects, using examples from the literature as illustrations. Before this elaboration, however, we provide a brief discussion of some relevant aspects of organic crystal structures and their roles in determining reaction course. 

Some typical CDFs are now discussed. The data stem from a sample of 48,312 organic crystal structures extracted from the CSD, each diagram being built on sets of 50,000-200,000 distance data. These very high numbers are indispensable small-population statistics is the most underhand enemy of the physical and social sciences. 

Corrected DFT methods the standard DFT calculation is supplemented by an empirical atom-atom term that reproduces correlation effects. They perform well because the missing effect in pure DFT is exactly pinpointed and circumscribed. Examples are a comparison of calculated lattice energies with experimental thermochemical data [46], including periodic orbital treatment, or the accurate reproduction of organic crystal structures without distortion [47]. 

Burzlaff, H. and Malinovsky, Y. (1997). A procedure for the classification of non-organic crystal structures I. Theoretical background. Acta Cryst. A53, 217-24. 

NEWCRYST FIZ Kadsruhe STN, Questel STN inorganic and organic crystal structures... 

Gavezzotti, A., Towards a realistic model for the quantitative evaluation of intermolecular potentials and for the rationalization of organic crystal structures. Part II. Crystal energy landscapes. Crystengcomm 2003, 5, 439—446. 

A survey of the frequency of occurrence in organic crystal structures of 75 hydrogen-bonded ring-type supramolecular synthons can be found in F. H. Allen, W. D. S. Motherwell, P. R. Raithby, G. P. Shields and R. Taylor, New J. Chem., 23, 25-34 (1999). 

Multiple molecular recognition sites will be necessary in order to gain a greater degree of predictability over organic crystal structures. 

Gavezzotti, A. Filippini, G. Computer prediction of organic crystal structures using partial X-ray diffraction data. J. Am. Chem. Soc. 1996, 118 (30), 7153-7157. 

Table 1. Occurences of 20 common solvents in organic crystal structures in decreasing order of Reproduced from (Nangia and Desiraju, 1999) by permission of The Royal Society of Chemistry.

Day GM, Chisholm J, Shan N, Motherwell WDS, and Jones W. An Assessment of Lattice Energy Minimization for the Prediction of Molecular Organic Crystal Structures. Cryst Growth Des 200, 4 1327-1340. 

M. Domagala, S. Grabowski, K. Urbaniak, G. MIoston. Role of C-H - S and C-H - N hydrogen bonds in organic crystal structures—the crystal and molecular structure of 3-methyl-... 

Figure 1.1.1 Experimental sublimation enthalpies and calculated lattice energies (kj mol-1) for 90 organic crystal structures.

SAg MW (kDa) Organism Crystal structure solved Zinc binding MHC II binding a/(3 chain Human TCRVP specificity Pso (h) (pg/ml) References... 

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