Extended coordination arrays

The ground state geometries in these complexes are often determined by a subtle balance of the energy released by an increase in coordination number and the energy lost by intramolecular repulsion. The question of versus bonding in the tris(cyclopentadienyl)uranium aUyls is one molecular example. The structures of the lanthanide tiicyclopentadienides represent another example in extended crystalline arrays. 

Increased functionality of the organometallic moiety will lead to more intricate supramolecular assemblies. A suggestive organometallic example is provided by tetra(p-cyanophenyl)silane, Si(C6H4CN-p)4, which forms a three-dimensional self -organized supramolecular network of interpenetrating double layers by coordination with silver ions [27] and a layered supramolecular structure with TiCU [28], both imposed by the directionality of tetrahedral silicon centers. Supramolecular assemblies are defined as "extended polymolecular arrays presenting a more or less... 

Schematic representation of defect clusters in Fei- jO. The normal NaCl-type structure (a) has Fe (small open circles) and O (large dark circles) at alternate comers of the cube. In the 4 1 cluster (h), four octahedral Fe" sites are left vacant and an Fe" ion (grey) occupies the cube centre, thus being tetrahedrally coordinated by the 40. In (c) a more extended 13 4 cluster is shown in which, again, all anion sites are occupied but the 13 octahedral Fe sites are vacant and four Fe occupy a tetrahedral array of cube centres.

A position sensitive detector (PSD) is employed, of which there are several types used effectively around the world. One type is essentially a square array of multianodes, as shown in Figure 1.6. By measuring the time-of-flight and the coordinates of the ions upon the PSD, it is possible to map out a two-dimensional elemental distribution. The elemental maps are extended to the z-direction by ionizing atoms from the surface of the specimens. The z position is inferred from the position of the ion in the evaporation sequence, so that the atom distribution can be reconstructed in a three-dimensional real space. 

Linear recognition is displayed by the hexaprotonated form of the ellipsoidal cryptand bis-tren 33, which binds various monoatomic and polyatomic anions and extends the recognition of anionic substrates beyond the spherical halides [3.11, 3.12]. The crystal structures of four such anion cryptates [3.11b] provide a unique series of anion coordination patterns (Fig. 4). The strong and selective binding of the linear, triatomic anion N3" results from its size, shape and site complementarity to the receptor 33-6H+. In the [N3 pyramidal arrays of +N-H "N- hydrogen bonds, each of which binds one of the two terminal nitrogens of N3-. 

In the periodic table for benzenoid hydrocarbons [7] the formulas C HS are arranged in an array with coordinates (ds, ,). The Dias parameters (ds) are found on a horizontal axis (increasing from left to right), while the numbers of internal vertices ( ) are on a vertical axis (increasing downwards). The table extends infinitely to the right and downwards. To the left the formulas form a line in the shape of an uneven staircase, which shall be referred to as the staircase-like boundary. 

Fig. 6 Porous coordination polymer (PCP) developed by Kitagawa and coworkers. The pores, which extend throughout the array, can be filled by C02 molecules (grey and red), allowing these materials to employ their high internal surface area as gas adsorbents [13]. Reprinted with permission...

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