Dumbbell chemical

Concept Rotaxane-like entities are created by the slippage protocol in which the cavities of macrocyclic polyethers dilate", at elevated temperatures, so as to allow their passage over the relatively bulky stoppers of chemical dumbbells (see Cartoon below). Similarly,... 

Rotaxanes are made of dumbbell-shaped and ring components which exhibit some kind of interaction originating from complementary chemical properties. In rotaxanes containing two different recognition sites in the dumbbell-shaped component it is possible to switch the position of the ring between the two stations by an external stimu-... 

Kinetically stable superarchitectures can be assembled by relying upon both noncovalent bonds and mechanical coercion. Thus, at elevated temperatures, rotaxane-like complexes (a) are generated when macrocycles slip over the stoppers of chemical dumbbells, while hemicarceplexes (b) are created when guests squeeze through the portals of hemicarcerands. 

Covalent metal-metal bonding in dusters is no longer a chemical curiosity as it was in ancient times when the dumbbell shaped cation [Hg2]2+ was one of the rare known examples. 

Practitioners of quantum chemistry employed both the visual imagery of nineteenth-century theoretical chemists like Kekule and Crum Brown and the abstract symbolism of twentieth-century mathematical physicists like Dirac and Schrodinger. Pauling s Nature of the Chemical Bond abounded in pictures of hexagons, tetrahedrons, spheres, and dumbbells. Mulliken s 1948 memoir on the theory of molecular orbitals included a list of 120 entries for symbols and words having exact definitions and usages in the new mathematical language of quantum chemistry. 

Irradiation of all kinds of solids (metals, semiconductors, insulators) is known to produce pairs of the point Frenkel defects - vacancies, v, and interstitial atoms, i, which are most often spatially well-correlated [1-9]. In many ionic crystals these Frenkel defects form the so-called F and H centres (anion vacancy with trapped electron and interstitial halide atom X° forming the chemical bonding in a form of quasimolecule X2 with some of the nearest regular anions, X-) - Fig. 3.1. In metals the analog of the latter is called the dumbbell interstitial. 

The p orbitals are dumbbell-shaped rather than spherical, with their electron distribution concentrated in identical lobes on either side of the nucleus and separated by a planar node cutting through the nucleus. As a result, the probability of finding a p electron near the nucleus is zero. The two lobes of a p orbital have different phases, as indicated in Figure 5.12 by different shading. We ll see in Chapter 7 that these phases are crucial for bonding because only lobes of the same phase can interact in forming covalent chemical bonds. 

Figure 13. Structures of dendrocatenanes (a), molecular knot, dumbbell knot (b), and Cu (c) resolved on chemically bonded-type CSP of AD.

Figure 6.7 A chemically controllable molecular shuttle. The macrocydic ring can be switched between the two stations of the dumbbell-shaped component by acid-base inputs.

This relation is the potential distribution theorem [73, 74], which gives a physical interpretation of the cavity function in terms of the chemical potential, and the excess interaction generated by the test particle, Y j>2 u(rv)> yia the ensemble average of its Boltzmann factor. In numerical simulation, the use of such a test-particle insertion method is of prime importance in calculating the cavity function at small distances and particularly at zero separation. Note that if the particle labeled 1 approaches the particle labeled 2, a dumbbell particle [41] is created with a bond length L = r2 n corresponding to a dimer at infinite... 

Rotaxanes 145 <1993CC1269>, 146 <1993CC1274>, and 147 <1996JA4931> incorporating Jt-electron-deficient bipyridinium-based dumbbell components and one or more 7t-electron-rich hydroquinone-based (and/or dioxy-naphthalene-based <1995CC747>) macrocyclic polyether counterparts have been assembled and their spectroscopic and electrochemical properties investigated in connection with the potential fabrication of chemically, photochemi-cally, and electrochemically active molecular devices <1996JA4931>. 

Let us consider another way of connecting molecules without chemical bond formation. If through a macrocy-clic molecule passes a linear one with bulky terminal groups, the system thus obtained represents a topological isomer of the type dumbbell in a ring (Fig. 31 ). Such... 

Figure 7.24. Comparison of conventional HRTEM (a), with HAADF-STEM (b). Also shown (c) is the chemical analysis of an individual CdSe dumbbell. The white circle shows the amorphous oxide region, and the surface of the nanocrystal is outlined in black. Unlike conventional HRTEM, it is also possible to label the individual nanocrystal facets, such as Cd-rich (001) and Se-rich (001 ). Reproduced with permission from McBride, J. R. Kippeny, T. C. Pennycook, S. J. Rosenthal, S. J. Nano Lett. 2004, 4, 1279. Copyright 2004 American Chemical Society.

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