Hexagons, pentagons and functions

TTF is an exceptional tt-donor and has become so extensively studied because it can be oxidized to the cation radical (TTF+ ) and dication (TTF+ ), both thermodynamically stable species, sequentially and reversibly within a very accessible potential window ( J = -F0.34 and = -F0.78 V, vs. Ag/AgCl in CH3CN), 

Let us here explore different strategies developed for synthesizing derivatives centred on the TTF core. The resulting molecules are called functionalized TTF molecules. The hrst strategy (S1) is based on the condensation of two dichalcogeno-late entities with C2CI4. This strategy was used in 1926 for the preparation of 

The set of strategies leading to symmetrically and asymmetrically functionalized TTF-derivatives is discussed next (see Fig. 2.5). Strategies S2 and S3 are known as cross-coupling reactions and S4 and S5 are termed condensation reactions. S2 and 

An additional entirely selective condensation synthesis for asymmetric TTF molecules is based on strategy S6, which consists in the reaction of an organotin dichalcogenolate with an ester in the presence of a Lewis acid such as MesAl (Yamada et al, 2004). A scheme of the reaction is given in Fig. 2.7. The method applies to the preparation of varied asymmetric IT Fs and can also be extended to the synthesis of selenium-containing analogues. 

It is possible to add carbon disulfide to acetylenes having at least one electron-attracting substituent R (in particular with R = —CF3) to give the product tetra-R-TTF (see Fig. 2.8) but in addition other compounds are obtained. This is our strategy S7. Their relative yields depend on the experimental conditions. However, in the presence of trifluoroacetic acid, the TTF derivative shown in the figure dominates. On the other hand, benzyne (CeHe with a triple bond) is known to cycloadd rapidly to CS2 giving DBTTF. 

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Previous theoretical investigations of pure boron clusters, based on ab initio quantum chemical and density functional theoretical methods, have shown that pure boron has stable structures forming a new class of boron materials. These structures can be classified into four topological groups convex, spherical, quasiplanar and tubular clusters. The new forms contain basically two units a pentagonal and an hexagonal pyramid. All these clusters can easily be generated by both units with the help of an Aufbau Principle proposed for boron. ... 

MoKoc data at four different temperatures, 100, 200, 293, and 373 K. The results showed that the two independent bond lengths of the buckminsterfullerene. common to a pentagon and a hexagon and d common to two hexagons, changed smoothly by —0.03 A as functions of temperature between 100 and 373 K the higher the temperature, the longer was d56 and the shorter was d, while the molecular diameter remained almost constant between 7.072 and 7.075... 

Fig. 3.20 The osmotic pressure is plotted as a function of the monomer density on a log-log scale for various chain-lengths. The 16-, 32- and 64-bead chains are represented by squares, pentagons and hexagons, respectively. For low densities in the experimental range, the pressure scales with an exponent 1.05, slightly below the Odijk prediction marked with an arrow. At high densities the exponent is 9/4 which is that of neutral chains. The errors are smaller than the points. The data show a very weak chain-length-dependence as in the experimental studies. (Taken from Ref. 158).

The general procedure in the analysis of molecular structure is then as follows. We assume a definite molecular model (a tetrahedron for the tetrachlorides, a hexagon or pentagon for cyclic compounds), and thence deduce the ratios of the different interatomic distances and the number of times each of them occurs in the molecule (periods). If, as in the case of tetrachlorides where the scattering power of the central atom may be neglected (e.g. CCI4), only one period exists, the distribution of intensity in the diffraction pattern may be expected to follow that of the simple function sinx/x (fig. 1). The first maximum occurs... 

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