Crystallographic unit cells

The description of the crystallographic unit cell is followed by probably the most important seetion of the file - the Cartesian eoovdinates of the atoms. 

Fig. 8.2 S implified structures of CaC2 l-lll (from (a) to (c)), displayed as derivatives of the NaCI type structure, neglecting the relation of their true crystallographic unit cells.

Figure 3. Projection showing the independent molecular units of the crystallographic unit cell of MNA down the polar axis (2).

Fig. 4. The crystallographic unit cell of tj6-C6H6Cr(CO)3(Cr(CO)3 units only]...

According to Eq. (1.22), the structure factor F(H) is the Fourier transform of the electron density p(r) in the crystallographic unit cell. The electron density p(r) is then obtained by the inverse Fourier transformation, or... 

Crystallographic quality ciystals of indinavir sulfate salt were grown hy slow diffusion of methanol into an ethanol/water solution. As confirmed by TG/IR results, the crystals obtained were a mixed mono-methanol / mono-ethanol solvate. The compound crystallized in the P2, space group, (monoclinic crystal system) with 2 molecules per unit cell. The cell constants were found to be a= 14.321(1)A, 6 = 10.091(1)A, c = 15.192(1)A, P = 95.50(1)°, andV=2185.5A. The calculated density was 1.200 g/cm. A view of the crystallographic unit cell packing is shown in Figure 4, with the solvent molecules omitted [7]. 

Crystallographic unit cell space P63/mmc Pm3n Fd3m... 

In the present article, we will survey the known synthetic procedures to intrazeolite semiconductor QD s and quantum supralattices (QS s this name has been chosen to refer to these structures, since they do not alter the crystallographic unit cell of the host, as the more common name of superlattice would imply). This is followed by two examples from our recent work concerning the I-VII pure and mixed halide system Ag,X-SOD (3) and the VI-VI system n(WC>3)-M56Y (Ozkar, S. Ozin, G.A. /. Phys. Chem., in press.). Some key properties of these materials will be briefly described that relate to QSE s, LFE s, electronic and vibrational coupling between QD s. The paper concludes with a very brief survey of some of the pertinent physics behind these early observations and how they might relate to the NLO properties of these materials. 

Fig. 2 Left. The basic 2D structure in the rod-like liquid crystals made by strongly polar molecules (the dipole moment directions are represented by arrows). The asymmetric rod-like molecules tend to form double layer structures in order to compensate dipole moments. Since the thickness of a double layer is smaller than twice the thickness of a single layer the resulting stress in the system is relieved by the in-layer modulation. Right. 2D structures in polycatenar rod-like liquid crystals. The ribbon like structure is formed by the asymmetric polycatenar molecules. To accommodate the additional alkyl chains layers become slightly bent. Both structures possess the body centered crystallographic unit cell...

Fig. 6 In the case of the oblique unit cell the intensity of the (—11) signal in the XRD pattern is usually higher than the intensity of the (11) signal (left). This indicates that the layer fragments in the crystallographic unit cell are inclined toward the shorter diagonal [the crystallographic plane (—11)] of the primitive unit cell (right). The electron density map was reconstructed from the X-ray data (see Sect. 3) bright regions are filled by the aromatic parts of molecules while the dark regions are filled by the alkyl chains. Dotted lines show midplanes of the blocks...

For phases made of tilted molecules, measurements show that the inclination of the unit cell can be higher or smaller than the molecular tilt. This is not surprising since the crystallographic unit cell is defined by complex interactions between the deformed layers. 

Fig. 11 XRD pattern of modulated SmCG general tilt structure with the synclinic tilt of molecules in the neighboring layers. The pattern corresponds to a structure with the body center oblique crystallographic unit cell note that for this phase the tilt of the unit cell is correlated to the tilt of the molecules...

To be able to predict the phases structural motif of the crystallographic unit cell is used (Fig. 15). Keeping the same crystallographic unit cell and rotating the blocks allows for an easy prediction of the XRD pattern for a variety of structures. For the considered crystallographic unit cell with a base at the position n> (a - b)/2 the structure factor is... 

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