Inter-stack interactions

Conduction in these ID metals is vulnerable to impurities, defects and thermal vibrations within each stack. Inter-stack interactions allow for increased dimensionality, and in some cases, superconductivity, by suppressing... 

As we show in Fig. 2 this relation holds as well for the two Al-based alloys studied here. This finding has consequences on the nature of the inter-atomic interactions. From a fee point of view, the hep structure has a stacking fault every second layer. The fact that relation (1) holds means that these stacking faults weakly interact, and therefore the range of the inter-atomic interactions should not go beyond the second neighbor shell whereas conventional central potentials require at least three atomic shells to differentiate the fee and hep stacking sequences. 

A second distinguishing feature of /l-solenoids is their inter-coil interactions. Their stacked coils are coordinated by a network of H-bonds. Usually, the coils in a given /1-solenoid have similar cross-sectional shapes, an arrangement that allows corresponding strands in successive coils to form parallel /1-sheets. The term /1-arc has been proposed for the turns between strands (Hennetin et al., 2006) and they also stack with inter-coil H-bonds, yielding so-called /1-arcades. The inter-coil distance (4.8 0.2 A) is determined by the distance between H-bonded /1-strands, which is the same on all sides of the solenoid. Consequently, /1-solenoids are straight and they contrast in this respect with other kinds of solenoids which mostly have curved shapes (Groves and Barford, 1999 Kobe and Kajava, 2000). 

Thus, the ion radical salt of BTDM-TTF (ET) with TCNQ has a high conductivity of 1.3 X 102 fl-1cm-1 at room temperature with metallic behavior down to 26 K (Rovira et al. 1994). (The unit of conductance is denoted as H-1, or ohm-1, or even mho, but mostly as S, i.e., siemens 1 S = 1 Ti1). The striking observation was made that the nature and molecular size of donor or acceptor have no substantial effect on the molecular distance within a stack (from 0.32 to 0.35 nm). Meanwhile, increasing the volume of a heteroatom leads to improving intermolecular interactions within given stacks. The enhanced inter-molecular interactions were indeed observed with the substitution of selenium for sulfur. The aforementioned orbital dispersion is more pronounced in the selenium-containing representatives. This arises from the more extensive overlap properties of selenium (Beer et al. 2001). 

High-frequency, p.m.r. spectroscopy has proved to be an extremely important tool in studies of the structures, conformations, and inter-and intra-molecular base-stacking interactions of nucleosides and nucleotides. The temperature dependence of the chemical shift of the base proton at position 6 (H-6) has been studied at 220 MHz for uridine (36), cytidine (38), and a number of their mono- (37, 39) and... 

This antiparallel double helix has a central cavity which is filled by the polyiodide chain or, in other terms, the polyiodide chain serves as a matrix around which the p-nitrophenyl-a-maltohexaoside molecules are arranged. The complex is stabilized by the inter- and intramolecular hydrogen bonds, the coordination of Ba2+ to hydroxyl groups and 0(5) atoms, and by the stacking interactions between p-nitrophenyl groups [583, 583 a]. 

The second family of superconducting materials is based on cation-radical salts of another donor, bis(ethylenedithio)-TTF (abbreviated BEDT-TTF or ET), which exhibit two-dimensional network mostly due to inter-stack S S interactions [100]. Another important feature of BEDT-TTF salts is their tendency to give polymorphs. For instance, (BEDT-TTF)2I3 salt affords four polymorphs (a, p, 0, and k phases), of which only the first undergoes metal-insulator transition, while the others are superconductors at ambient pressure (see Chapter 10 of this book). It is quite surprising that of all numerous BEDT-TTF structural analogs synthesized to date, only two salts of unsymmetrical derivatives, DMET [101] and MDT-TTF [102], led to superconductors. 

In discotics, the interdisk stacking interaction is several orders of magnitude stronger than the inter-columnar interactions, because of the phase separation induced by the side-chains whose van der Waals interactions are much weaker. Generally, long polymers are obtained via discotics that have strong and specific intermolecular interactions, either via a large aromatic core or via additional specific intermolecular... 

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