Orthorhombic cell

Another polymorph of triethylamylose with dichloromethane or chloroform has also been studied 175). Here the number of guest molecules decreases from 8 to 4 per unit cell and the solvent molecules are now located in interstitial sites. The orthorhombic cell has space group P2l2l2l. 

Description of a hexagonal unit cell (ah, ch cell edges) in terms of an ortho-hexagonal cell (equivalent orthorhombic cell a0, b0, c0) (see Fig. 3.10). 

Figure 3.10. The relation between a hexagonal cell and an equivalent orthorhombic cell is shown by means of their projections on the a, b plane.

Figure 24. X-ray diffraction pattern (in the inset the 2D image) of the polyethylene sample recovered by the laser-assisted high-pressure reaction in the pure liquid monomer. The two measured sharp lines nicely fit the polymer diffraction pattern having a orthorhombic cell (Pnam) defined by the lattice parameters reported in the figure.

Draw an orthorhombic cell, and within that cell draw a [211] direction and a (021) plane. 

Fig. 11. Orthorhombic distortion of tetragonal HoNi2B2C (a) upon cooling from 15 K to 1.5 K the neutron diffraction reflection (332) splits into two peaks, (b) Schematic presentation of the distortion a,b — original tetragonal axes dashed line tetragonal basal plane —f shift of the Ho atoms leading to the orthorhombic cell with the axes onh- Thick arrows Ho magnetic moments in the commensurate c-axis modulated structure...

GdNi crystallizes in the orthorhombic CrB type of structure (space group Cmcm). The Gd atoms are located on the 4c sites with point symmetry mm (0, yGd % 0.14, ). The Ni atoms also occupy the 4c sites with yNi 0.43 (see e.g. Buschow (1980)). It is interesting to note that among the RNi compounds there exists a second type of orthorhombic structure. Only the compounds with R from La to Gd crystallize in the CrB type. The compounds with R from Dy to Tm and Y show the less symmetric FeB type with space group Pnma (see e.g. Burzo et al. (1990)). As reported by Blanco et al. (1992) TbNi crystallizes in a monoclinic intermediate structure. Figure 26 shows the orthorhombic unit cell and the atomic arrangement of the CrB type of structure. (The shown orthorhombic cell is not the... 

A previous examination of a synthetic calcium mordenite 15) revealed an orthorhombic cell. A synthetic strontium mordenite 16) had a C-centered orthorhombic cell although Kerr 12) reported that a few crystals giving electron diffraction patterns corresponding approximately to the body-centered structure Immm) have been synthesized hydro-thermally from aluminosilicate gels containing strontium similar to those gels which yielded a strontium-mordenite. ... 

Figure 16.9. Location of some of the equivalent points and symmetry elements in the unit cell of space group Pnali. An open circle marked + denotes the position of a general point xyz, the + sign meaning that the point lies at a height z above the xy plane. Circles containing a comma denote equivalent points that result from mirror reflections. The origin is in the top left comer, and the filled digon with tails denotes the presence of a two-fold screw axis at the origin. Small arrows in this figure show the directions of a1 a2, which in an orthorhombic cell coincide with x, y. The dashed line...

Fig. 17.6. Maps of in-plane crystallographic orientation of the orthorhombic cell in the crystalline part of the polyethylene structure (a) short-term and (b) longterm implanted acetabular cups (cf. the central photographs). Compare the average direction of c-axis orientation and the motion direction shown on the respective maps and on the photographs of the acetabular cups, respectively...

Evaluation of the fibre patterns showed that the glucan chains have a stretched form with twofold screw symmetry and a fibre repeat period of 0.835 nm, as predicted by model building and conformational analysis. The differences between the polymers exist therefore in their chain packing. A monoclinic unit cell with a=0.581 nm b=1.00 nm Y=96° was derived for polymorph I and orthorhombic cells for II and III respectively with the base plane axes a=0.502 nm b=0.963 nm f°r II and a=0.457 nm b=0.865 nm for III. These cells contain 4 glucose residues, and on account of spatial considerations the ribbon-like chains in projection on the base plane were supposed to be oriented with the longer axis parallel to the b-axis (i. e. with the pyranose rings near parallel to the bc-plane) in both polymorph II and III, whereas in polymorph I a diagonal position appeared more favourable. 

Diborontetrachloride molecules contain two bonded B atoms with two Cl atoms bonded to each B atom giving a planar ethylene-like molecule. The bond angles are close to 120°. The colorless liquid decomposes above 0°C. The orthorhombic cell contains four molecules, D, Pbca, a0 = 11.900, b0 = 6.281, and cD = 7.690 A, at -165° C. The cell is face centered (Figure 4.22) giving the simple notation 3P(o). 

Figure 4.21. A projection along aQ of the face-centered orthorhombic cell, 3P(o) for SO2.

Figure 4.22. A projection along ba of the face-centered orthorhombic cell of B2CI4. The average heights of the B—B bonds are at 0 (and 100) and at 50 (side faces).

Figure 4.23. A projection along a0 of the orthorhombic cell of IF7. The dimensions for the IF7 molecules are shown.

Figure 5.13. The 2,2P1/201/2(o) structure of aragonite (CaCCh). (a) A projection of the orthorhombic cell along the c axis. Ca atoms are dark small atoms. The triangular ions are apparent with C atoms small light atoms, (b) A perspective view of the cell.

The mineral enargite (Cu3AsS4), an important ore for Cu and As, has a 2 2PT3/4 i/4(o) structure. It is similar to wurtzite except that each T layer occupied is one-quarter filled by As and three-quarters by Cu. The stoichiometry indicates the occupancies of T sites. The structure is shown in Figure 6.9. Because of the simple ordered pattern of partial filling by As and Cu there are four packing layers in the packing unit and two molecules per cell. It also has open C channels. The orthorhombic cell contains two molecules, Q lv, mn2, a0 = 6.46, b0 = 7.43, and c0 = 6.18 A. 

Figure 7.15. A projection of the orthorhombic cell of NH4HF2 along its ca axis. (Source R.W.G. Wyckoff, Crystal Structures, Vol. 2, ed., Wiley, New York, 1964, p. 280.)...

Figure 7.31. A projection of the orthorhombic cell of CuGeC>3 along ca.

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