Tetragonal crystal systems

Tetragonal crystal system, 8 114t Tetragonal lattice structure, of silicon, 22 482... 

Grayish-white, heavy powder tetragonal crystal system density 4.96 g/cm melts at 450°C insoluble in water. 

Glassy solid tetragonal crystal system hygroscopic density 2.1 g/cm melts... 

Colorless crystalline solid tetragonal crystal system hygroscopic density 2.50 g/cm3 (tetrahydrate 1.71 g/cm ) tetrahydrated salt loses water of crystallization on heating further heating to 550°C causes decomposition soluble in water, tetrahydrate more soluble in water (30.5g/100g at 30°) than the anhydrous salt insoluble in alcohol. 

Continuing with our survey of the seven crystal systems, we see that the tetragonal crystal system is similar to the cubic system in that all the interaxial angles are 90°. However, the cell height, characterized by the lattice parameter, c, is not equal to the base, which is square (a = b). There are two types of tetragonal space lattices simple tetragonal, with atoms only at the comers of the unit cell, and body-centered tetragonal, with an additional atom at the center of the unit cell. 

The x-ray diffraction powder pattern for Mg2NiH4 was indexed on the basis of a tetragonal crystal system with unit cell dimensions of a = 6.464 A and c = 7.033 A. The measured density was 2.57 g/cm3, compatible with four formula units of Mg2NiH4 per unit cell. 

Term symbols, 26-27, A7-A12 Tetrachloroiodate anion. 209 Tetragonal crystal system, 75, 78 Tetragonal symmetry. 403-404 Tetrahedral complexes, 401-403, 418-420, 441. 448-455, 474-477... 

In the tetragonal crystal system the base-centered lattice (C) is reduced to a primitive (P) one, whereas the face-centered lattice (F) is reduced to a body-centered (I) cell both reductions result in half the volume of the corresponding unit cell (rule number three). 

Figure 2.41. The differences between the observed and calculated 20 values plotted as a function of 20 without (open circles) and with (filled triangles) specimen displacement correction. The corresponding values of the unit cell parameters and the specimen displacement parameter are indicated on the plot. The material belongs to the tetragonal crystal system.

Table 2.16. Reflection conditions for the tetragonal crystal system.

Thus, there is a fundamental difference between the accuracy of structure amplitudes obtained from single crystal and powder diffraction data. The former are always resolved, i.e. there is only one combination of indices, hid, per Bragg peak, whereas in the latter some reflections may be fixlly or partially overlapped. The intensities of individual reflections hkl may still be recovered from powder diffraction data but their accuracy is critically dependent on both the degree of the overlap and the quality of the pattern. Obviously, the absolute overlapping of some reflections makes it impossible to obtain the individual intensities regardless of the quality of data, and only the combined total intensity is known (e.g. reflections 43/ and 05/ in both the cubic and tetragonal crystal systems). 

The quadratic form of Eq. 5.2 in the hexagonal crystal system is found in Eq. 5.4 and its analogue in the tetragonal crystal system is... 

In this example, we consider a powder diffraction pattern of CeRhGcs, collected using Mo Ka radiation. We already discussed a part of this pattern in problem 2, Chapter 5. The alloy crystallizes in a tetragonal crystal system with a = 4.3979(1) and c = 10.0329(3) A. Files with experimental data saved... 

FIGURE 1.14 Seen here is the hk0 zone diffraction pattern from a crystal of M4 dogfish lactate dehydrogenase obtained using a precession camera. It is based on a tetragonal crystal system and, therefore, exhibits a fourfold axis of symmetry. The hole at center represents the point where the primary X-ray beam would strike the film (but is blocked by a circular beamstop). Note the very predictable positions of the diffraction intensities. All the intensities, or reflections, fall at regular intervals on an orthogonal net, or lattice. This lattice in diffraction space is called the reciprocal lattice. 

Tetragonal crystal system the holohedric group Dgh, and those sub-groups which do not belong to classes 1, 2, and 3 Dgh Dg, Cgyj, Dai Cgh, Cg, Sg... 

Yellow brass-colored or bronze-colored crystals. Metallic, greenish sheen. Tetragonal crystal system, d 4. ] -4.3. mp 950. Specific heat 0.]291. Hardness 3,5-4.0. Solubtein nitric acid, but dissolves faster in aqua regia. Practically jnso] in hydrochloric acid. 

Large water-clear crystals, with a diamond glitter. Tetragonal crystal system. Sublimes at room temperature. Instantaneous decomposition with water, accompanied by formation of PH3 (see p. 529) and HI. Must therefore be stored out of contact with atmospheric moisture. 

Table XXVI summarizes two different series of wcio-tetraphenylporphyrin derivatives that crystallize in the tetragonal crystal system. The compound, space group, a, c, and unit cell volume are listed for each member. Series a, the four-coordinate species, has H2TPP as the parent compound. The existence of the series is expected and solid solutions of H2TPP and the metallo derivatives listed are readily formed . All members of this series have Ruf core conformations with substantial displacements of the carbon atoms. The second series is a substantial series of five- or six-coordinate complexes of which [Sn(TPP)Cl2] is the prototypical ordered example with symmetry. We first concern ourselves with the subset that have been catalogued as having I4/m as the space group. The phenyl groups of adjacent I-centered molecules make equivalent ligand pockets above and below the porphyrin plane. The pocket size is adequate for small (mono- or diatomic) axial ligands. Most of the species listed in Table XXVI(b) are seen to be five-coordinate hence the complexes display disorder in the crystal and...

In the tetragonal crystal system there are two types of Bravais lattice P and I). AU their symmetrical transformations may be obtained from the symmetrical transformations for orthorhombic lattices if one sets ni = ri2 and takes into account that base-centered and face-centered orthorhombic lattices become simple and body-centered tetragonal ones, respectively. 

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