Triclinic space groups

Formula Chemical class Chemical type Na7AlH2(C03)4F4 Crystal system Acid carbonate Mineral group Space group Triclinic, pseudohexagonal... 

Formula Chemical class Chemical type (Cu,Co),(C03)(OH), Anhydrous carbonate with hydroxyl or halogen (AB),(X03>Z, Crystal system Mineral group Space group Triclinic Malachite PI or Pi... 

Formula Chemical class Chemical type Zn,2Ca(U02)(C03)3(0H)22 4H20 Crystal system Hydrated carbonate with hydroxyl or halogen Mineral group Miscellaneous Space group Triclinic PI... 

Hartung and Rapthel [64] described the crystal structure of the mesogenic 2-methylthio-5-(4 -n-butyloxyphenyl)-pyrimidine which forms a monotropic smectic A phase. The chemical structure of this compound is presented in Fig. 5. The compound crystallises in the triclinic space group PI with two molecules per unit cell. The molecules adopt a fully stretched and nearly planar form. The pyrimidine ring is nearly planar. The dihedral angle between the phenyl and the pyrimidine rings is 22.7°. The molecules are arranged parallel to each other. 

Ethyl a-cyano-4-[2-(2-pyridyl)ethenyl]cinnamate (7 OEt) also crystallizes with /3-centrosymmetric-type packing yielding photoreactive crystals and, upon photoirradiation (>410 nm), is converted into the /3-hetero-type dimer (7 OEt-dimer) nearly quantitatively. The 7 OEt-dimer (space group PT, triclinic) has the structure which is predicted from the crystal structure of 7 OEt (space group PT, triclinic). 

The structure of nigellidine (Section 12.10.15.1) was unambiguously determined by X-ray diffraction of its methyl iodide and methyl chloride salts. The methyl chloride salt gave better data, and its crystals formed the triclinic space group PI with a = 9.334(3), b = 14.050(4), c = 14.862(4) A, a = 81.83(2)°, f3 = 74.80(2)°, and 7 = 87.26(2)°. The methyl attached to O-l comes from the methyl chloride used for the salt formation the natural product exists as a zwitterion <1995TL1993>. 

The Sn6P6 cluster 19c crystallizes in the triclinic space group PI. It forms a distorted hexagonal Sn6P6 prism with three-coordinated Sn and four-coordinated P atoms (Fig. 20) (39), that is, the structure is topologically identical with that of solvent-free 17 (see Fig. 18). 

The four-membered Al2As2 heterocycle 27a was the first derivative to be structurally characterized (58). It crystallizes in the triclinic space group PI. The Al2As2 ring is puckered, with pyramidally coordinated As atoms and tetrahedrally surrounded A1 centers (Fig. 23). The amine groups at aluminium are cis-oriented to each other, which is probably due to the steric demand of the silyl groups. The average... 

The Ca/Sn-mixed metalated phosphanide-phosphandiide cluster 43 crystallizes in the triclinic space group PI (71). It consists of a trigonal Ca2SnP2 bipyramid, where the phosphandiide P centers serve as ju -bridging centers to the metals. The two phosphanide ligands, however, are. -bridging between two Ca and Ca/Sn centers (Fig. 32). Both Ca ions are octahedrally coordinated. 

The unit cell considered here is a primitive (P) unit cell that is, each unit cell has one lattice point. Nonprimitive cells contain two or more lattice points per unit cell. If the unit cell is centered in the (010) planes, this cell becomes a B unit cell for the (100) planes, an A cell for the (001) planes a C cell. Body-centered unit cells are designated I, and face-centered cells are called F. Regular packing of molecules into a crystal lattice often leads to symmetry relationships between the molecules. Common symmetry operations are two- or three-fold screw (rotation) axes, mirror planes, inversion centers (centers of symmetry), and rotation followed by inversion. There are 230 different ways to combine allowed symmetry operations in a crystal leading to 230 space groups.12 Not all of these are allowed for protein crystals because of amino acid asymmetry (only L-amino acids are found in proteins). Only those space groups without symmetry (triclinic) or with rotation or screw axes are allowed. However, mirror lines and inversion centers may occur in protein structures along an axis. 

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. 

Figure 2.23 Models of packing of chains in form IV of sPP according to space groups (a) P1148 and (b) C2149. Arrows indicate crystallographic twofold axes, present in (b) and lost in (a). In (a) chains are rotated by 6.5° according to direction indicated by arrows and continuous and dashed lines show triclinic and monoclinic unit cells, respectively.

Structural Characterization. Compound 70a crystallized in the triclinic space group PI with two crystallographically independent molecules in the asymmetric unit, each with similar gross conformations, Fig. 12. The five-membered chelate ring on each molecule is essentially planar with the... 

It is interesting that tris-acetylacetonato-Yb(III)-monohydrate tends to retain solvent molecules. Thus if Yb(acac)3 3HaO is recrystaUized from acetone or benzene, one molecule of the solvent is present for two molecules of Yb(acac)3 H2O. The hemibenzene solvated Yb(acac)3 of composition [Yb(acac)3 H2O O.bCeHs] also crystallizes in triclinic space group PT, hke the unsolvated complex, with a =8.728, 6 = 8.435, c = 15.623 A, and a = 95.95°, /S = 107.72° and y =96.18° but with two formula units per unit cell (84). 

It has been earlier mentioned that the octacoordinated Pr(III) ion in triclinic NH4[Pr(TTA)4] -HaO crystal (space group Z = 2) possesses essentially... 

The structures of the radical cation salts of the TTF derivatives were determined by X-ray crystallographic analyses <1997SM1871>. The (CIO4) and (SbFs) salts of 45 presented, respectively, as monoclinic CZIm space group) and triclinic (FI space group) black single crystals. A coplanar 2-D network characterized by short intermolecular S- N (3.27 A) and S- S (3.58 A) contacts and a column structure formed by a dimer of the donor 45 with... 

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