Crystal Structures of Organic Compounds

Structure retrieval or generation Crystal structures of organic compounds can be found in the Cambridge Crystallographic Datafiles (http //www.ccdc.cam. ac.uk/). Those that does not exist may be generated by 3D rendering software. The 3D structural coordinates of biomacromolecules can be retrieved from Protein Data Bank (http //www.rcsb.org/pdb/). 

Gorbitz CH and Hersleth HP. On the Inclusion of Solvent Molecules in the Crystal Structures of Organic Compounds. Acta Crys B 2000 B56 526-534. 

Cambridge Structural Database (CSD). Cambridge Crystallographic Data Centre, University Chemical Laboratory, Cambridge, UK. Electronic database of crystal structures of organic and metallorganic compounds. www.ccdc.cam.ac.uk. 

Many crystal structures of host compounds or solvate compounds with 1,4-dioxane as well as a wide range of organic structures bearing a 1,4-dioxin, 1,4-oxathiin, or 1,4-dithiin core have been determined by single crystal X-ray diffraction. 

The very last example here refers to the, so-called, organic zeolites. There are several structures which belong to this class of inclusion compounds and their physicochemical properties are remarkable, being of particular interest to separation science. An example of crystal structure of the compounds is given in Fig. 11.10 [9]. 

Since 1995, more than 250 single-crystal X-ray structures of organic compounds (excluding their metal complexes) relevant for this chapter were deposited in the Cambridge Structural Database (CSD). Therefore, only brief overview of the reported structures is given here. 

Gavezzotti, A. (1994b). PROMET3. A program for the generation of possible crystal structures from the molecular structure of organic compounds. University of Milano, available upon request. [183, 186]... 

The Patterson function is a map that indicates all the possible relationships (vectors) between atoms in a crystal structure. It was introduced by A. Lindo Patterson " in 1934, inspired by earlier work on radial distribution functions in liquids and powders. In crystals the directionality as well as the lengths of vectors between atoms (atomic distances) can be deduced. By contrast, in liquids and powders the geometric information that can be obtained is limited to interatomic distances, because in these the molecules are randomly oriented. While the use of the Patterson function revolutionized the determination of crystal structures of small molecules in the 1930s to 1950s, direct methods are now the most widely used methods for obtaining structures of small organic molecules. The Patterson function, however, continues to play an essential part in the determination of crystal structures of inorganic compounds and macromolecules. It is also very useful when the structure of a small molecule proves difficult to solve by direct methods. 

This chapter presents an overview of the crystal structures of inorganic compounds in which actinide polyhedra are directly coordinated by phosphate or arsenate tetrahedra. Arsenates are considered here for comparative purposes, because of the very similar structural roles played by arsenate and phosphate ions. Structural data are taken mainly from the Inorganic Crystal Stmcture Database [6] and the published literature. Entries from the Powder Dififtaction File of the International Centre for Diffraction Data [7] have been consulted in the case of compounds whose structures may reasonably be inferred. Mixed organic-inorganic compounds [8] and polyoxometalates are not addressed phosphites, phosphinates and arsenites also fall outside the scope of this chapter. Data are tabulated for a given structure type, with phosphates separated... 

State S = 15/2 as a result of the ferromagnetic interaction between the central Cr (S = 3/2) ion and the six peripheral (5=1) metal ions, as was expected [24]. Unfortunately, the crystal structure of this compound has not been fully solved mainly because of a large disorder on the organic ligands. However, the magnetic properties below 1 K were investigated and a slow relaxation of the magnetization was evidenced [25]. 

PPN] [FeRu3H(CO)i3] is an air-stable, black, crystalline solid. It is insoluble in nonpolar organic solvents such as hexane and soluble in polar organic solvents such as diethyl ether, dichloromethane, and tetrahydrofuran. Solutions of [PPN] [FeRu3H(CO)i3] are stable in air for several weeks. The compound is best characterized by its IR spectrum, which shows the following bands in dichloromethane solution 2073 (w), 2032 (s), 2013 (s), 1998 (s), 1970 (sh), 1940 (sh), 1844 (w), 1809 (br) cm"1. The H nmr spectrum at -80° in acetone-of6 exhibits a single resonance at 5 = -15.6 ppm.12 The crystal structure of the compound as determined by a neutron diffraction study has also been reported.12... 

Differences in shape lead to considerable differences in the ranges of structures adopted, and these modify the questions that computer modelling is seeking to address. Many molecular crystal structures have already been determined the Cambridge Structural Database (Allen et ai, 1991 Allen and Kennard, 1993) contains 140268 crystal structures of organic and organo-metallic compounds (April 1995 release). Various statistical analyses suggest that over 90% of these structures contain only one independent molecule in the... 

For some time four modifications of cinnamic acid, which possess different melting points, have been known. It has been shown recently that three of the forms, which melt at 68°, 58°, and 42°, respectively, are crystallographic modifications of a single acid. When any one of them is melted and the liquid formed is seeded with a crystal, the solid which s parates on cooling has the melting point of the crystal used to induce crystallization. The fact that apparently four forms of the acid existed aroused much interest and led to a number of investigations, because the results appeared to be at variance with the accepted theory as to the structure of organic compounds. 

A. Gavezzotti, PROMET "A Program for the Generation of Possible Crystal Structures from the Molecular Structure of Organic Compounds , A. Gavezzotti, J. Am. Chem. Soc. 1991, 113, 4622. 

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