Two-dimensional sheets

The dihydrate of the tetramer is particularly stable and is, in fact, the bishydroxonium salt of tetrametaphosphimic acid [H30]J[(NH)4P4-06(0H)2] the anion of which has a boat configuration and is linked by short H bonds (246 pm) into a two-dimensional sheet (Fig. 12.29). The related salts M4[NHP02)4].- H20 show considerable variation in conformation of the tetrametaphosphimate anion, as do the 8-membered heterocyclic tetraphosphazenes (NPX2)4 (p. 537), e.g. 

In diamond, carbon is sp hybridized and forms a tetrahedral, three-dimensional network structure, which is extremely rigid. Graphite carbon is sp2 hybridized and planar. Its application as a lubricant results from the fact that the two-dimensional sheets can slide across one another, thereby reducing friction. In graphite, the unhybridized p-electrons are free to move from one carbon atom to another, which results in its high electrical conductivity. In diamond, all electrons are localized in sp3 hybridized C—C cr-bonds, so diamond is a poor conductor of electricity. 

The silicates are a large class of solids of great importance in industry as well as science, particularly geology. The prototype silicate is quartz consisting of Si04 tetrahedra which share their comers and edges and are arrayed in various three-dimensional patterns depending on the temperature. In other crystalline minerals the tetrahedra are linked in one-dimensional chains, or two-dimensional sheets. The arrays in these latter cases are combined with various metal ions. 

The complex consists of infinite zigzag chains of Na-As-Na-As units in which the Na-As-Na angle is essentially linear [173.6(1)°] and the As-Na-As angle is 121.5(1)°. The sodium atoms achieve a tetrahedral geometry by coordination by two molecules of dioxane that bridge between adjacent chains to give a two-dimensional sheet arrangement. 

Two-dimensional periodic organization of eukaryotic and prokaryotic ribosomes occurs under special conditions in vivo (Byers, 1967 Kress et al., 1971 Taddei, 1972 O Brien et al, 1980) or in vitro (Barbieri, 1979 Clark et al, 1982). The two-dimensional sheets have been analyzed by image-reconstruction techniques (Kiihlbrandt and Unwin, 1982 Clark et al, 1982). 

Structural composites can be combinations of homogeneous and composite materials. Laminar composites are composed of two-dimensional sheets that generally have a preferred... 

N—H---O(H)—N, O—H---0=C and N—H---0=C are among the possibilities. Such interactions can have a variety of consequences for crystal packing, which can involve dimers, two-dimensional sheets, three-dimensional networks etc. Examples have been cited. 

The chemical and physical properties of ribosomes are well characterized (for reviews see The exact understanding of their function, however, still lacks a detailed molecular model. Appropriate methods such as image reconstruction from electron micrographs of two-dimensional sheets, or X-ray structure analysis, all depend on the crystallizability of the material. 

The large size of ribosomal particles is an obstacle for crystallographic studies, but permits direct investigation by electron microscopy. A model (Fig. 13) obtained by three-dimensional image reconstruction of two-dimensional sheets (e.g. ) may be used for gradual phasing of low resolution crystallographic data. 

Brossard L, Clerac R, Coulon C, Tokumoto M, Ziman T, Petrov DK, Laukhin VN, Naughton MJ, Audouard A, Goze F, Kobayashi A, Kobayashi Ft, Cassoux P (1998) Interplay between chains of S = 5/2 localised spins and two-dimensional sheets of organic donors in the synthetically built magnetic multilayer )l-(BETS)2FeCl4. Eur Phys J B 1 439 52... 

Figure 9 Construction of the energy bands of undistorted one dimensional chains and two dimensional sheets of (a) the platinum amine halide system where the z2 orbital is used, and (b) the Cu02 sheet where the x2 - y2 orbital is used. Notice the strong similarities in orbital character, and compare with Figure 7b.

Fiber-Matrix Composites. As shown in Figure 1.75, there are two main classifications of FMCs those with continuous fiber reinforcement and those with discontinuous fiber reinforcement. Continuous-flber-reinforced composites are made from fiber rovings (bundles of twisted filaments) that have been woven into two-dimensional sheets resembling a cloth fabric. These sheets can be cut and formed to a desired shape, or preform, that is then incorporated into a composite matrix, typically a thermosetting resin such as epoxy. Metallic, ceramic, and polymeric fibers of specific compositions can all be produced in continuous fashions, and the properties of the... 

When three corners of each Si04 tetrahedron are shared, a two-dimensional sheet... 

In the crystal structure of (BEDT-TTF)6[AuBr2]6Br(TIE)3 [AuBr2], Br, and TIE molecules construct two-dimensional sheets by means of Au- -I and Br- -I secondary bonds, as shown in Figure 5.10. There are two types of [AuBr2] anions and only one of them participates in the formation of Au- I interactions by coordination of four TIEs at the central Au atom, thus being incorporated in the sheet. The Au- - I distances, of 3.271 and 3.369 A, are shorter than in the previous example. The other type of [AuBr2] is located apart from the sheets and incorporated in the conduction layer. Both kinds of [ AuBr2]" anions are almost perpendicular to the two-dimensional sheets. 

Fig. 8. Structure of succinamide. The NHa group form two hydrogen bonds directed at the 0 =C group linking the molecules in a two-dimensional sheet...

Layer silicates or /j/iy/fo-silicates Two-dimensional sheets of [Si04] tetrahedra sharing three oxygen atoms Kaolinite, ALi(OH)8(Si4010) Talc, Mg3(OH)2(Si4O10) Muscovite, KAl2(OH)2(AlSi3O10)... 

Properties of Lipids and Lipid Bilayers Lipid bilayers formed between two aqueous phases have this important property they form two-dimensional sheets, the edges of which close upon each other and undergo self-sealing to form liposomes. 

Closely related to the use of models is the corresponding one of stereoviews to illustrate molecular perspective. The increased availability of molecular data and the use of computers to generate stereoviews has made their use routine in journal accounts of structure determinations. Unlike models, no matter how useful, stereo-views have the ability to capture the depth of a three-dimensional structure on a two-dimensional sheet of paper. An increased number of stereoviews has been included in this edition. 

The formation of infinite two-dimensional sheet structures in copper(I) compounds (Figure... 

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