Lattices chain host

The electrochemical intercalation/insertion is not a special property of graphite. It is apparent also with many other host/guest pairs, provided that the host lattice is a thermodynamically or kinetically stable system of interconnected vacant lattice sites for transport and location of guest species. Particularly useful are host lattices of inorganic oxides and sulphides with layer or chain-type structures. Figure 5.30 presents an example of the cathodic insertion of Li+ into the TiS2 host lattice, which is practically important in lithium batteries. 

Crystals of tris(o-phenylenedioxyde)cyclotriphosphazene (97) can act as hosts for the inclusion of a number of organic polymers, e.g. cis-1,4-poly butadiene, 1,4-polyisoprene, polyethylene (PE), poly(ethylene oxide) (PEO) and polytetrahydrofuran. X-ray studies of the PE and PEO inclusion compounds show that the polymer chains are extended along the tunnel-like voids of the host lattice. The formation of clathrates appears to be limited by the tunnel dimension of the host crystal lattice. The melting points of the inclusion adducts appear to be higher than those of either the pure host or the pure... 

Our studies on the generation of novel urea, thiourea, and selenourea-anion inclusion compounds have shown that novel anionic host lattices can be constructed from urea derivatives and many types of anions as building blocks. The versatility of urea, thiourea, or selenourea as a key component in the construction of novel host lattices is clearly demonstrated by the occurrence of many new types of linkage modes, which include various discrete units, chains or ribbons, and composite ribbons with corresponding anions. These motifs are shown in Tables 14, IS, and 16, respectively. 

As mentioned above, in urea/thiourea-anion inclusion compounds both urea and thiourea molecules adopt various linkage modes not only of self-assembled hydrogen-bonded chains or ribbons but also of composite ribbons with the corresponding anions. The results show that comolecular aggregates of urea or thiourea with other neutral molecules or anionic moieties can be considered as fundamental building blocks for the constructions of various types of novel host lattices. 

As indicated by Equation (1), intercalation reactions are usually reversible, and they may also be characterized as topochemical processes, since the structural integrity of the host lattice is formally conserved in the course of the forward and reverse reactions. Typically, these reactions occur near room temperature, but this is in sharp contrast with most conventional solid-state synthetic procedures which often require temperatures in excess of 600 °C, the term Chemie Douce has been coined to describe this type of low-temperature reaction. Remarkably, a wide range of host lattices has been found to undergo these low-temperature reactions, including framework (3D), layer (2D), and linear chain (ID) lattices. 

The host lattice CeMgAlnO 7 has the magnctoplumbite structure, LaP04 the mon-azite stnicture, and GdMgBsOio a structure consisting of a two-dimensional framework of BO3 and BO4 groups in which the Mg ions ate in octahedral coordination and Gd in ten coordination [19]. The Gd polyhedra form isolated zig-zag chains. The shortest Gd-Gd intrachain distance is about 4 A, the shortest Gd-Gd interchain distance 6.4 A. 

The loss of energy to the substrate material is brought about by two processes. One is by excitation and ionization of electrons. The other is by elastic collisions with nuclei. The results of violent collisions may be the displacement of atoms in the host lattice along the ion path setting up a chain reaction as long as the kinetic... 

In view of the earlier work of Lawton and Powell on unit cell dimensions and contents of channel-type clathrates, the guest molecules are expected to be severely disordered within the cylindrical cavities. First, they may be packed head-to-head or head-to-tail second, the length of the chain-like molecules is unlikely to match the unit translation imposed by the ordered host lattice. As a consequence, host-guest functional interactions will differ within successive unit cells and a dramatic decrea of chiral discrimination is bound to ensue for lack of unique stereospedfic complementarity. 

Doping may impose further structural effects that depend on the size and nature of the dopant species. Although there may still not be complete accord on the crystal structure of lithium-doped polyacetylene, it appears that at low doping levels entropic factors are important in inserting a small nonaggregating ion, such as Li", into polyacetylene (PAc), with the dopant occupying sites with minimal strain or disruption of the host lattice. Iodine, on the other hand, in the form of IJ and IJ (and possibly higher polyiodides), produces structures in which anions cluster in columns or sheets to form intercalated layers between polymer chains. ... 

Simulations reveal structural interactions between the migrating dopant ion and the host lattice in which polymer chains respond to the migrant by distorting from planarity. As would be expected, this interaction increases rapidly with the flexibility of the chains. In Section 6.2 we see that in nonconjugated polymers (i.e., those with no n electronic component to favor chain planarity), the host dopant interaction plays an essential role in the jump mechanism in migration. 

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