Triclinic system

Iodine is a bluish black, crystalline soHd having a metallic luster. It is obtained in shiny flakes or prills that can be easily cmshed to powder. Iodine crystallines in rhomboidal plates belonging to the triclinic system. 

Two macromolecular computational problems are considered (i) the atomistic modeling of bulk condensed polymer phases and their inherent non-vectorizability, and (ii) the determination of the partition coefficient of polymer chains between bulk solution and cylindrical pores. In connection with the atomistic modeling problem, an algorithm is introduced and discussed (Modified Superbox Algorithm) for the efficient determination of significantly interacting atom pairs in systems with spatially periodic boundaries of the shape of a general parallelepiped (triclinic systems). 

For biaxial crystals, similar results are obtained as with uniaxial crystals. The exception to this rule is that in monoclinic and triclinic systems, the polarization directions need not be parallel to faces or to the bisectors of face angles. If the prominent faces or edges of an extinguished crystal are not parallel to the axes of the initial polarizer, the extinction is said to be oblique (Fig. 3d). 

Block-shaped black crystals with a distinct metallic luster are formed which upon crystallographic study are found to crystallize in the triclinic system with lattice constants as follows a = 7.786 (1) A, fe = 13.033 (3) A, c = 18.590 (4) A, a = 110.09 (2)°, 0 = 90.21 (2)°, y = 105.27 (2)°, and Vc = 1699.8 (6) A3. These lattice parameters indicate that the crystals contain 0.5 molecules of TCE in the formula unit as is the case for isostructural (BEDT-TTF)2ClO4(TCE)0 5 in which Vc = 1689.8 A3.10 The electrical properties of this material indicate that they are metallic from room temperature to 90 K at which point a metal-insulator transition occurs. 

Fig. 32. Triclinic system, a. Unit cell typo. 6. Strontium hydrogen tartrate hydrate SrH2(C4H406)a.4H20. Class 1. c. CuS04.6Ha0. Class T. d. 1,4 dinitro 2,5 dibromo-...

Triclinic sometimes called anorthic). Crystals lacking symmetry of any kind naturally have the most c general type of unit cell, the three axes of which are all inclined to each other at different angles and unequal in length. The addition of a centre of symmetry does not alter the situation, for this most general type of unit cell has a centre of symmetry and is appropriate for this class also. These two classes, 1 and 1, constitute the triclinic system (Fig. 32). 

Molecules of the ineso form of 2,3 dibromobutane Br(CH3)HC— CH(CH3)Br have a centre of symmetry (I) as their only element of symmetry j (Stevenson and Schomaker, 1939), resembling in this respect crystals belonging to the holohedral class of the triclinic system. It is worth noting that the d and l isomers are not asymmetric they possess one twofold axis.j... 

Where there is more than one cell of the same volume (and shape appropriate to the crystal system) which will account for all the reflections, as in monoclinic and triclinic orystals (see Fig. 76), the most nearly rectangular cell will usually prove the most convenient to accept. There has been much discussion of conventions in the triclinic system the convention recommended bj" International Tables (1952) is that all three angles of the cell should be obtuse, and the direction cosines of the axes with the fill] zone axi should all be positive. 

Hibbert [15] assumed that the labile form of nitroglycerine belongs to the triclinic system, while according to Flink [19] the stable form has orthorhombic bipyramidal crystals. 

For the triclinic system, only the two point groups l(Ci) and 1(C,) are possible since all others have too much symmetry. 

This requirement excludes PI in the triclinic system as well as all those monoclinic space groups associated with crystal classes m and 2hn. Thus,... 

In crystals of the triclinic system all of the asymmetric units are aligned in the same manner and there are no axes of symmetry. 

An additional problem with triclinic systems is concerned with the process of fitting theory to experiment, for here it is necessary to reproduce all six independent components of the magnetic tensor simultaneously rather than, perhaps, just the three principal moments in more symmetric crystals. Coupled... 

Di-p-tolyl tellurium dichloride, (CH3.C6H4)2TeCl2,1 is obtained in a similar way to the phenyl compound. It separates from absolute alcohol as small needles or plates of the triclinic system, M.pt. 160° to 167° C., soluble in chloroform, benzene, toluene, xylene or ligroin, sparingly soluble in methyl alcohol. 

An X-ray crystallographic analysis of DAD single crystals shows a triclinic system with the non-centrosymmetric space group P1 and that the direction of polarization of DAD in the molecular crystal is perfectly aligned in one dimension. 

Molecular and crystal structure of DAD are shown in Figure 3 and 4. DAD crystallize in a triclinic system with the non-centrosymmetric space group P1. The direction of polarization of DAD in the molecular crystal is perfectly aligned in one dimension as shown in Figure 4. X-ray crystal analysis of DAD also shows the existence of two hydrogen bonds between adjacent molecules, 0 1--H... 

Merten 14> has extended the theory for the general case of a biaxial, polyatomic crystal. His theory is worked out in detail for crystals of the orthorhombic system and all crystal classes of higher symmetry, but not yet for crystals of the monoclinic and triclinic systems. 

Six types of spectra are theoretically possible in minerals of the orthorhombic, monoclinic and triclinic systems (McClure, 1959). However, for electric dipole transitions only three spectra are usually distinguished. These are the a, P and y spectra obtained when light is polarized along each of the three indicatrix axes, which in orthorhombic minerals such as olivine and orthopyroxene correspond to the three crystallographic axes. The majority of the spectra of minerals described in chapters 4 and 5 consist of polarized spectra measured in the three mutually perpendicular directions corresponding to a, P and y polarized light... 

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