Pyramidal arrays

Cu(NH3)3C03] Cu in tetragonal-pyramidal array with basal ... 

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 hydrogen bonds, each of which binds one of the two terminal nitrogens of N3-. 

A more common arrangement for EM4 species is the square pyramidal array with E occupying the apical vertex (51), which is related to the octahedral E2M4 (52) and EM5 (53) arrangements. Note that 51 is the structural isomer of 46 where the E atom adopts the apical rather than the basal position. These compounds are listed in Tables XVIII-XX, whereas Table XXI lists a number of more complicated molecules that have several... 

FIGURE 1 (a) Microstructure of a hexagonal GaN pyramid array, as revealed by low magnification TEM. 

The trimetallic complex [Fe3(CO)8(p-PPh)2(PF3)] has been obtained from the corresponding [Fe3(CO)8(p-PPh)2(MeCN)J compound by displacement of MeCN (method G). The structure, which is based on a square-pyramidal array of three iron and two phosphorus atoms, consists of isomers whose interconversion has been studied by variable-temperature 19F and 31P NMR spectroscopy. A trimetallic PF3 complex containing mercury bonded to two metals results from the reactions... 

The monoxides SnO (the form stable under ambient conditions is blue-black in colour) and PbO (red form, litharge) possess layer structures in which each metal centre is at the apex of a square-based pyramidal array (Figure 14.27). Each metal centre bears a lone pair of electrons occupying... 

In order to further develop the coordination chemistry of anions and to extend recognition of anionic substrates beyond the spherical halides, an ellipsoidal macro-bicyclic cryptand Bis-Tren (14) was designed, whose hexaprotonated form was expected to bind various anions [9, 10]. Indeed, potentiometric and spectroscopic measurements showed that (14)-6H complexes a number of monovalent and polyvalent anions. The strong and selective binding observed for the linear triatomic anion NJ may be attributed to its complementarity to the molecular cavity of (14)-6H . As confirmed by crystal structure determination, NJ forms the cryptate [N c (14)-6H ] (15), in which the substrate is bound inside the cavity by two pyramidal arrays of three hydrogen bonds, which hold the two terminal... 

Southwell WH. (1991) Pyramid-array surface-relief stmctures producing antireflection index matching on optical surfaces. J Opt Soc Am A 8(3) 549—553. 

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