Triclinic system space group

The crystal structure of /i-oxo-bis[tris(p-chlorophenyl)(l,l,l-trifluoro-2,4-pen-tanedionato-0,0 )antimony(V)] 1/2 chloroform has been determined375. The compound crystallizes in triclinic system, space group PI. The binuclear Sb-complex consists of two distorted octahedra joined by an O atom which is situated at inversion centre the Sb-O-Sb bridge is linear. This seems to be the first example of a linear Sb-O-Sb linkage. The bridged oxygen and one of the oxygens of/3-diketone occupy trans-positions. The/3-diketonate forms two distinct Sb-0 bonds ... 

Imai and co-workers (301-303) were the first to use the [Ni(dmit)2 system in combination with a cation radical of a-nitronyl nitroxide, namely, p-lV-ethyl-pyridinium a-nitronyl nitroxide (p-EPYNN) (Scheme 15). The (p-EPYNN)-[Ni(dmit)2] compound is obtained by metathesis reaction between p-EPYNN.I and (n-Bu4N)[Ni(dmit)2] in acetonitrile. It crystallizes in the triclinic system, space group PI with a = 11.647(4), b= 11.986(3), c= 12.047(6) A,... 

Ten years ago, some salts of the type (DMET)2X, where DMET is the unsymmetrical molecule (2b -7c) and X = Pp6, BF4, Au(CN)2 etc., have been prepared and studied. Most of these are crystallized in the triclinic system (space group PI), in which the DMET molecules form columnar stacking with some dimerization (see Figure 3.3,11). There are interstack interactions stronger than those of Bechgaard salts (i.e. shorter S S and S Se contacts) [442]. 

X-ray crystal diffraction shows that the disilanes rBuBr2SiSlBr2/Bu and /ButSiSibfBu crystallize in a triclinic crystal system (space group Pi) and adopt Q symmetry. Selected theoretical and experimental geometric parameters are given in Table 3. The structure of the iodo compound as determined by X-ray diffraction is depicted in Fig. 3. 

Seven crystal systems as described in Table 3.2 occur in the 32 point groups that can be assigned to protein crystals. For crystals with symmetry higher than triclinic, particles within the cell are repeated as a consequence of symmetry operations. The number of asymmetric units within the unit cell is related but not necessarily equal to the number of molecules in a unit cell, depending on how the molecules are related by symmetry operations. From the symmetry in the X-ray diffraction pattern and the systematic absence of specific reflections in the pattern, it is possible to deduce the space group to which the crystal belongs. 

Triclinic Space Groups. The triclinic crystal system allows no axis of rotation of order higher than one, namely, 1 or 1. Since neither of these can give rise to any additional symmetry, there are just two triclinic space groups. Both are primitive and are designated FI and FI. 

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. 

TABLE 11.9 Classification of Space Groups Based on Systematic Absences for the Triclinic, Monoclinic, and Orthorhombic Systems... 

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

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... 

Crystals of tetramethylantimony(dimethylthiophosphinate) belong to triclinic system with space group PIAar>. The antimony atom has a distorted trigonal bipyramidal geometry while phosphorus atom is surrounded by a distorted tetrahedral environment. 

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