Donor packing

Fig. 5 Donor packing and Fermi surface for BO compounds, (a) Face-to-face packing dotted lines indicate the CH---0 hydrogen bonds), (b) side-by-side contacts dotted lines indicate the short S---S atomic contacts), and calculated Fermi surfaces of (c) (BO)2Cl(H20)3. Calculated Fermi surface of (BO)2.4l3 is depicted in Fig. 3b...

In two-component assemblies, the interaction, between donor and acceptor molecules or donor molecules and anions, affects their molecular arrangement and physical property as well. Polymeric anions may govern the donor packing, and magnetic anions often interact with the conduction -electrons. This is one of the interesting aspects of the study of organic molecular conductors not only the freedom of molecular design but also the combination of molecules. 

So far 33 ET SCs have been developed with either the discrete or polymerized anions (Table 10.1). The donor-packing pattern, which determines the electronic structure of the complex, are classified into ot, P, y, 0, k, etc. In the following sections... 

Variations on the a helix in which the chain is either more loosely or more tightly coiled, with hydrogen bonds to residues n + 5 or n + 3 instead of n + 4 are called the n helix and 3io helix, respectively. The 3io helix has 3 residues per turn and contains 10 atoms between the hydrogen bond donor and acceptor, hence its name. Both the n helix and the 3to helix occur rarely and usually only at the ends of a helices or as single-turn helices. They are not energetically favorable, since the backbone atoms are too tightly packed in the 3io helix and so loosely packed in the n helix that there is a hole through the middle. Only in the a helix are the backbone atoms properly packed to provide a stable structure. 

Carrier generators in molecular conductors have been associated for a long time to a partial charge transfer between the HOMO (or LUMO) electronic band and other chemical species. These systems are known as two-component molecular conductors. Tetrathiofulvalene derivatives are versatile systems for the formation of molecular organic conductors due to their electron donor capacity by transferring one u-electron from the HOMO orbital, and to their planar shape that promotes their stacking as a consequence of the n-n orbital overlap. The electronic properties of these salts are essentially determined by the packing pattern of the donor molecules which, in turn, depends on the counter-ion. 

Haloarenes routinely form XB. The same holds for haloheteroarenes and when the heteroaromatic ring is positively charged, the halogen becomes a particularly good XB donor [89-94]. This strategy has been applied with particular success in order to control the packing of bromo- and iodo-... 

Packing in / Im 2 H20 also shows some distinct features that may be related to the existence of the ionic species in the crystal. Hydrogen bonding is, of course, a primary feature (Fig. 43). An extensive network exists in this crystal which has the form of endless chains rather than that of loops usually found for the similarly double-faced (H-bond donor and acceptor) alcohols (cf. Fig. 19). As already mentioned, the carboxylate function has four connections, while its neutral —COOH neighbor maintains three H-bond contacts. The inner water molecule with respect... 

Interestingly, the introduction of two bromomethyl functions in 4- and 5-positions of ethylen-l,3-dithiole-2-thione leads to a packing determined by weak interactions involving also the bromine atoms. One I2 molecule behaves as an acceptor towards S and as donor towards the second I2 molecule, which in turn behaves as donor towards the a c Br orbital (Figure 13). Intermolecu-lar S- -Br, CFF Br and L -I contacts make up a three-dimensional network.480 Reaction of 5,5-dimethyl-2-selenoxoimidazoline-4-one with iodine provided the first structurally characterised compound of the type [RR C Se — I-I].32 The Se-I bond is shorter (269.9 pm) and the I-I contacts are longer (296.2 pm) than in 1 1 adducts of dialkylselenides with iodine (see Chapter 8.2). 

The electron-donor molecule most studied as a component of cation-radical salts is BEDT-TTF. Over 50 superconducting salts containing this molecule have been reported in the literature. Several distinct packing motifs [6-8] of the BEDT-TTF radical cations have yielded superconducting salts, but the most studied of these are... 

Scheme 2 Four common packing motifs of the BEDT-TTF molecule. The black bars represent and end-on view of the molecule, looking down the long molecular axis. The a-phase, which is quite similar to the 0-phase, is characterized as a herringbone structure, the P -phase contains stacks of slipped dimers, the K-phase contains orthogonally arranged dimers, and the P"-phase is characterized by canted stacks of donor molecules...

Fig. 2 Packing diagram of the layered structure of kl-(BEDT-TTF)2Cu(CF3)4(TCE) (top). The packing motif of the BEDT-TTF electron donor molecules (lower left). The anion layer contains both disordered [Cu(CF3)4] anions and neutral TCE solvent molecules (lower right). In all cases, hydrogen atoms have been omitted for clarity...

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