Orthorhombic crystal systems

The crystal properties of pseudoephedrine hydrochloride were determined with a GE model XRD-6 x-ray diffractometer using Zr filtered MoK radiation on a crystal grown from water.8 Pseudoephedrine hydrochloride has an orthorhombic crystal system belonging to the P212121 space group. The cell dimensions are a=25.358 A, b=6.428 A, c=6.901 A with each cell containing four molecules. 

Orthopedic devices, 3 721-735 joint replacement, 3 727-735 Orthopedic marrow needles, 3 743-744 Orthophosphate (PO4), in soil, 11 112 Orthophosphates, 18 830-841 20 637 magnesium, 18 839 manufacture of, 18 853-855 Orthophosphate salts, 18 836 Orthophosphoric acid, 18 815, 817-826 condensation of, 18 826 properties of, 18 817-819 solubility of boron halides in, 4 140t orf/zo-phthalic resins, 20 101, 113 formulation of, 20 102 Orthorhombic crystal system, 8 114t Orthorhombic phosphorus pentoxide, 19 49 Orthorhombic structure, of ferroelectric crystals, 11 95, 96 Orthorhombic symmetry, 8 114t Orthosilicate monomers, in silicate glasses, 22 453... 

In all other crystal systems we encounter the same general situation, namely, that a few space groups (69, in fact) can be uniquely identified from a knowledge of diffraction symmetry and systematic absences, while the rest form mostly pairs, or small groups that are indistinguishable in this way. Table 11.9 lists for the triclinic, monoclinic, and orthorhombic crystal systems the uniquely determined space groups and the sets with identical systematic absences. 

Nanocrystallite S -ZrW MooiOg was prepared through a precursor route. The characterization by powder X-ray diffraction (XRD) and selected area electron diffraction (SAED) shows that the compound is orthorhombic crystal system with cell parameters a=0.8969(7) nm, b=0.7011(8) nm, c=0.596(l) nm. The possible space group is Pnnm (58) or Pnn2 (34). The compound is a metastable phase depending on temperature and time. 

Positions of Bragg peaks are established from the Braggs law as a function of the wavelength and the interplanar distances, i.e. (/-spacing. The latter can be easily calculated from the known unit cell dimensions (section 2.8). For instance, in the case of the orthorhombic crystal system permissible Bragg angles are found from... 

Now consider the orthorhombic crystal system. Simple analysis of Eq. 2.32 indicates that the following groups of reciprocal lattice points will have identical reciprocal lattice vector lengths and thus, are equivalent in terms of the corresponding Bragg angle ... 

Considering an orthorhombic crystal system, the equivalency relationships established above (section 2.10.3) also satisfy Eq. 2.1J4 i.e. 

Table 2.13. Reflection conditions for the orthorhombic crystal system (Laue class mmm).

The maximum size of the unit cell edges can be estimated from the d-spacing of the first Bragg peak (t/max) observed in the diffraction pattern. In the majority of low symmetry cases (triclinic through orthorhombic crystal systems), the maximum size of the unit cell edge should not exceed... 

In the orthorhombic crystal system the unit cell dimensions should be such that a[Pg.440]

N is defined as a non-zero value in the keyword SELECT, e.g. in the orthorhombic crystal system SELECT=5 results in the following basis sets (1,2,5), (1,3,5), and (2,3,5). Additional sets that are added to the basis set when MONOSET keyword value is greater than 3,4, 5 or 6, respectively. 

Consider the powder diffraction pattern collected from a ground Hf2Ni3Si4 powder, which is shown in Figure 6.46. The pattern has been indexed in the orthorhombic crystal system and the unit cell dimensions are a = 5.18, b = 13.65 and c = 6.85 A. An analysis of the systematic absences indicates that the following groups of reflections have non-zero intensity ... 

The compound VO(CH3COO)2 crystallizes in the orthorhombic crystal system with a = 14.066, b = 6.878, c = 6.925 A. Its gravimetric density is less than 2 g/cm. The powder diffraction pattern (data files Ch6Pr09 VO-acetate.raw and Ch6Pr09 VO-acetate.xy) is shown in Figure 6.47. The extracted structure amplitudes (data file Ch6Pr09 VO-acetate.hkl) are also found on the CD. Solve the crystal structure of this material. 

Most organic compounds crystallize in the monoclinic or orthorhombic crystal systems, which contain substantial macroscopic anisotropies, and thus the singlecrystal CD technique cannot be applied, although our method of measurement may be useful if the macroscopic anisotropies are not very large. An alternative way to obtain crystalline-specific information is to examine the microcrystalline state. Measurements can be usually made either in nujol mull or KBr disc form, where microcrystals are dispersed randomly either in nujol or in a KBr microcrystalline matrix. The method was developed and applied to inorganic complexes by Mason [34], Bosnich [35], and Kuroda [9,10], and since then its application to metal complexes has been carried out sporadically [36,37]. Recently, the technique has become popular in the field of organic chemistry as well, probably stimulated by our work [38]. An alternative technique recently developed by us is diffuse reflectance CD (DRCD) which will be briefly described in V.B.2. 

Crystals of endo-Su (a-Sig) are intense lemon-yellow, rhombic plates and belong to the orthorhombic crystal system. The molecules are arranged to form a pseudohexagonal close packing which accounts for the higher density of the endo-Sis crystal. Crystals of exo-Sig (PSu) are monoclinic. The crystal and molecular structure data are summarized in Table 15. A detailed analysis and modeling of the intermolecular forces in 12 sulfur allotropes... 

Orthorhombic crystal system the holohedric group and those sub-groups which do not belong to classes 1 and 2 (three specific directions are defined) Dsh D2, C2v... 

The primitive orthorhombic lattice can be thought of as arising from a primitive monoclinic lattice with the added restriction that the third angle is also 90°. In that case, all the unit cell translation vectors are 90° to one another but have different lengths. In the orthorhombic system, one can construct a C-centered cell, which can also be described as an A- or B-lattice by an interchange of the orthogonal axes. In addition, there can also be an all-face-centered F-lattice structure and a body-centered I-lattice. Thus for the orthorhombic crystal system there are four unique Bravais lattices, P, I, F, and C. 

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