Chlorine molecule crystal structure

The crystal structures of four chlorinated derivatives of di-benzo-p-dioxin have been determined by x-ray diffraction from diffractometer data (MoKa radiation). The compounds, their formulae, cell dimensions, space groups, the number of molecules per unit cell, the crystallographic B.-factors, and the number of observed reflections are given. The dioxin crystal structures were performed to provide absolute standards for assignment of isomeric structures and have been of considerable practical use in combination with x-ray powder diffraction analysis. 

Figure 5.2 (a) Electron density contour map of the CI2 molecule (see Chapter 6) showing that the chlorine atoms in a CI2 molecule are not portions of spheres rather, the atoms are slightly flattened at the ends of the molecule. So the molecule has two van der Waals radii a smaller van der Waals radius, r2 = 190 pm, in the direction of the bond axis and a larger radius, r =215 pm, in the perpendicular direction, (b) Portion of the crystal structure of solid chlorine showing the packing of CI2 molecules in the (100) plane. In the solid the two contact distances ry + ry and ry + r2 have the values 342 pm and 328 pm, so the two radii are r 1 = 171 pm and r2 = 157, pm which are appreciably smaller than the radii for the free CI2 molecule showing that the molecule is compressed by the intermolecular forces in the solid state. 

An X-ray crystal structure of 73 indicated that the molecule is located on an mm2 site in which the two chlorine atoms adopt an axial position while the carbon atoms are disordered, a consequence of the (R,R)- and (A,A)-racemic mixture <2000CC1117>. 

Fig. 12-7.—The arrangement of water molecules in the chlorine hydrate crystal. Some of the water molecules are at the corners of pentagonal dodecahedra, as indicated. Some additional water molecules (circles) are needed to complete the structure. Hydrogen bonds are formed along the edges of the d decahedra, and also between adjacent dodecahedra and between the dodecahedra and the interstitial water molecules.

Benzene forms an addition compound with chlorine, CgHg C. The crystal structure is monoclinic, with two molecules per cell,... 

The atoms in a molecule of table salt (NaCl), for example, are of different sizes. The sodium (Na) atoms are smaller than the larger chlorine (Cl) atoms, so the sodium atoms become packed in between the larger chlorine atoms. The resulting shape is a crystal, building-block structure. The atoms are as tightly packed as possible, but there is still a lot of space inside the crystal structure because of the difference in size of the atoms involved. 

Crystal structures of some bromine-substituted compounds were selected from the CSD according to the criteria (b) to (e) used for the chlorinated compounds. The number of minimum bromine atoms per molecule [criterion (a)] was reduced to 3 for C(sp3)—Br bonds and to 2 for C(sp2)—Br bonds. With these restrictions 43 observations were listed for C(sp3)—Br bonds with a mean value of 195.6 pm and a large standard deviation of 6.5 pm. The individual values range from 179.4 pm to 224.8 pm. The extreme values are listed in Table 41. The mean distance of 47 C(sp2)—Br bonds is 189.0 pm with a standard deviation of 2.2 pm. The individual values vary from 185.1 to 195.9 pm. Some examples of these recent crystal studies are given in Tables 41 and 42. 

Concerning the two examples discussed here, we know only the crystal structure of 1,3,5-trichlorobenzene. There are four molecules in the unit cell. One molecule is identical with the asymmetric unit 76). This means that in the solid, due to the crystal field effects, the three chlorine atoms are crystallo-graphically inequivalent ... 

The naphthalene molecule is planar. The distance between substituents in the 1- and the 8-positions (and in the equivalent 4- and 5-positions) is shorter compared to substituents in e.g., the 1- and 2-positions. The 1-/8- and 4-/5-positions are often called the peri-positions after the Greek word peri which means near . Bulky substituents in these positions will sterically interact and cause a distortion of the molecule. For example, in the crystal structure of 1,4,5,8-tetraCN (CN-46) the chlorine atoms are positioned slightly above and under the plane of the naphthalene ring [157]. In octaCN (CN-75) the aromatic ring system is also remarkably distorted [185,186]. These distortions, as well as the unequal distribution of the u-electrons, most probably influence the physical properties and enhance the chemical as well as the metabolic reactivity of the compound. 

R = -C4H9) has been reported to crystallize in four polymorphic forms (Brandt et al. 1982). In the copper phthalocyanines Pigment Blue 15, containing no Cl, is isomorphous with Pigment Blue 15 1, which on an average contains 0.5-1.0 atoms of chlorine per molecule (Hao and Iqbal 1997). Recognition of this phenomenon can be useful, for instance, in attempting to work out the crystal structures of unknown polymorphic forms. 

In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride (100) and of tellurium tetrachloride on twinned crystals (65, 66) were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties (e.g., 66,161,168,169,219,220, 412), as well as the synthetic potential of the compounds. In contrast to the monomeric molecular i//-tbp gas phase structures with C2v symmetry (417), the solid state structures of both are polynuclear. As the prototype of the chlorides and bromides of selenium and tellurium, crystalline tellurium(IV) chloride has a cubane-like tetrameric structure with approximate Td symmetry (Fig. 1). Within the distorted TeCla+a octa-hedra the bonds to the triply bridging chlorine ligands are much longer than to the terminal chlorines. The bonding system can be described either covalently as Te4Cli6 molecules, or, in an ionic approximation, as [(TeCl Cn4] with a certain degree of stereochemical activity of the lone pairs toward the center of the voluminous cubane center (65, 66). 

FIGURE 15.8. The role of chlorine in aligning molecules (Ref. 18). The similarities in the crystal structures of (a) chlorine and (b) monoclinic 1,4-dichlorobenzene are shown. The two structures are held together in similar ways by Cl Cl interactions. (Reproduced with the permission of G. R. Desiraju and Elsevier Science Publishers BV, Academic Publishing Division, Amsterdam, The Netherlands.)... 

Chlorinated triarylmethyl triradicals Sedo, J., Yentosa, N., Ruiz-Molina, D., Mas, M., Molins, E., Rovira, C. and Veciana, J. (1998). Crystal structures of chiral diastereo-isomers of a carbon-based high-spin molecule. Angew. Chem. Int. Ed. 37, 330-333... 

---