Cubes isomers

On the other hand, the luminescence properties of the cube and chair isomeric forms of [Ag4l4(PPhj)4] (40) have also been reported by Henary and Zink [116]. Solid samples of the cube and chair forms emit at 455 and 418 nm, respectively, at 12 K. The emission has also been assigned to a d-s silver-centered state modified by metal-metal interaction. The lower emission energy of the cube form compared with the chair form can be accounted for by the higher delocalization over the d and s orbitals of the silver(I) centers for the cube isomer. For the cube form, each silver has three neighboring silver centers. However, for the... 

Figure 83 Projection of the potential energy surface for isomer A of [M(bidentate)2 (unidentate) on to the (p-Ojj plane (in degrees). The five faint contour lines are for successive 0.02 increments in X above the minimum, and the five heavy contour lines are for successive 0.2 increments above the minimum, at D. = 0.9. The locations of the dodecahedron (D) and cube (C) are indicated...

Trifluoromethyl)phenylcopper was found to be an octamer by consideration of the kinetics of its decomposition, and by cryoscopy and vapor pressure osmometry in benzene solution 36). Its F NMR spectrum in ether at room temperature is a sharp singlet. Consequently, the suggested structure is a central copper cube with equivalent bridging benzotri-fluoride groups. The initial decomposition product, Cu8( n-CF3CgH4)e, is considered to be a Cu(0)—Cu(I) octanuclear cluster compound 36). For the octameric m-(trifluoromethyl)phenylcopper, the tetrameric ortho isomer, and pentafluorophenylcopper tetramer, the F NMR spectra were found to vary with temperature. The changes are not considered to involve important structural alterations, but only variations in solvent complexes and rotamer populations 32, 37). The spectra also... 

In Figure 2.14a, the 48-vertex structure of the great rhombicuboctahedron is divided into two sets of 24 points, coloured to distinguish two sets related by the inversion operation. Each set of 24 vertices now exhibit O symmetry and are examples of the chiral polyhedra based on the snub cube structure, displayed as the ri-isomer as a projection in Figure 2.14b and as a perspective drawing in Figure 2.14b. 

For 2-methyl cyclohexanone (1), the first case in Table 8, the average priority value allows one to easily predict the main product of the reaction as the (IS, 2S) isomer, although one atom of the substrate occupies a low priority cube (OH). The enantiomeric (1R, 2R) product may be formed in small quantities, but formation of the other diastereoisomer (IS, 2R) and its enantiomer (1R, 2S) are clearly less likely due... 

Figure 21 Each panel shows the similarity function for all four isomers of Nijv clusters when comparing with (a) an icosahedral cluster, and (b-d) a spherical fragment of the fee crystal when the center of the fragment is placed at (b) the position of an atom, (c) the middle of a nearest-neighbor bond, and (d) the center of the cube, respectively...

The crystal structure of this isostructural series of catechol complexes consists of discrete [M(catechol) 4 ] dodecahedra, a hydrogen bonded network of 21 waters of crystallization and sodium ions, each of which is bonded to two catecholate oxygens and four water oxygens. Of the possible eight coordinate poly-hedra, only the cube and the dodecahedron allow the presence of the crystallographic 4 axis on which the metal ion sits. As depicted in Figure 5 and verified by the shape parameters in Table IV, the tetrakis(catecholato) complexes nearly display the ideal D2d molecular symmetry of the mmmm isomer of the trigonalfaced dodecahedron. 

One of the most unexpected results obtained was for Pg, where the much-studied cubic (0 ) form corresponds to a shallow local minimum in the energy surface. Simulated annealing led, however, to the Czv structure (Fig. 4b), which is much (ca. 1.7 eV) more stable. This wedge structure, which may be viewed as a (distorted) cube with one bond rotated through 90°, is a structural unit in violet (monoclinic, Hittorf) phosphorus [48]. A second isomer of Pg ( >21, Fig. 4a) is also much more stable than the cubic form. There is a striking analogy between the structures of the Pg-isomers and those of the valence isoelectronic hydrocarbons (CH)g. The cubic form of the latter (cubane) has been prepared by Eaton and Cole [49], and can be converted catalytically to the wedge-shaped form (cuneane) [50]. 

Two types of molecular boxes featuring (ethylenedi-amine)Pd(II) corners and polypyridyl linkers were described.One uses roughly rectangular tetrapyridy ligands as walls for an open-ended cube. (7) Multiple isomers were obtained, and one is shown in Fig. 6. By carrying out the synthesis in the presence of an appropriate guest molecule, the isomer distribution can be... 

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