Isostructural materials

TCNQ salts however, this was only a substitute for a more quantitative approach through the calculation of transfer integrals (see Section VII) or for the direct observation of the charge density between molecules (see Section XI). However, in series of isostructural materials such as the Bech-gaard salts, it is clearly possible to estimate intra- and interstack interactions... 

The primary difficulty inherent in this issue is the small niunber of materials with suitable crystal structures and lattice constants. Some transition metals and ceramics, such as Ni, Cu, Fe, and cBN (Table 5, Ch. 3), are the few isostructural materials with sufficiently similar lattice constants (mismatch <5%). In addition, the extremely high surface energies of diamond (ranging from 5.3 to 9.2 J m for the principle low index planes) and the existence of interfacial misfit and strain energies between diamond films and non-diamond substrates constitute the primary obstacles in forming oriented two-dimensional diamond nuclei. Earlier attempts to grow heteroepitaxial diamond on the transition metals were not successful. The reasons may be related to the high solubility/ mobility of C in/on the metals (for example, Fe, Co, or the... 

The work of Sanders et al. (1984), Jackson and Catlow (1988) and Tomlinson et al. (1990) showed that with Born model potentials it is possible accurately to reproduce the crystal structures of silicates including zeolites. A typical example is shown in Plate I which illustrates the calculated and experimental structures of a purely siliceous (i.e. pure Si02 polymorph) zeolite, silicalite. (A closely related, isostructural material, ZSM-5, which contains a low concentration of Al is an effective isomerization and hydrocarbon synthesis catalyst.) The agreement between theory and experiment is evidently good more discussion follows in Chapter 9. 

TABLE 3. Comparison of Average Heats of Atomization (Hg, in kcal/g-atom) and Energy Gaps (Eg, in eV) of Several Classes of Isostructural Materials... 

To determine the effect of OMSs within a MOF on H2 adsorption, Suh and coworkers synthesized three porous isoreticular MOFs (SNU-4, SNU-5, and SNU-5) with the same NbO-type net topology. The formation of OMSs can be controlled by precisely selecting different activation conditions. It was observed that in the presence of OMSs, the MOF clearly has a higher H2 adsorption on both gravimetric and volumetric bases, probably due to a stronger interaction between OMSs with H2 molecules, because the reduction of framework mass cannot completely explain the enhanced volumetric uptake. Note that for isostructural materials, volumetric capacity calculations can elucidate the effects of OMSs without discriminating against the additional mass. 

Few examples of complex structures containing homonuclear Ge-Ge or Si-Si bonds have been described in the Hterature (see Fig. 14.1b). Isostructural ternary materials with the formula (A = Na, K M" =Si, Ge Q=S, Se, Te)... 

Another important group of oxide materials with a very low electrical conductivity is the oxide dielectrics. A number of these are based upon the perovskites, MXO3 or M0 X02. The archetype of these materials is BaTiC>3, which has a high dielectric constant, or relative permittivity to vacuum, the value at room temperature being 1600, and commercial use is made of the isostructural PbTi(>3 and ZrTi03 which form solid solutions, the PZT dielectrics. These materials lose their dielectric properties as the temperature... 

Chloroprene (2-chloro-l,3-butadiene 105), which is a mass-produced, inexpensive industrial material, is an excellent precursor to a variety of terminal allenes 107 [97]. The palladium-catalyzed reaction of 105 with pronucleophiles 106 in the presence of an appropriate base gave the terminal allenes 107 in good yields (Scheme 3.53). The palladium species generated from Pd2(dba)3-CHC13 and DPEphos was a good catalyst for these reactions of chloroprene. In contrast, (Z)-l-Phenyl-2-chloro-l,3-buta-diene, which is isostructural with the bromo-substrate 101, was nearly inert under these conditions. There is no substituent at the vicinal ris-position to the chloride in 105, which allows oxidative addition of the C-Cl bond in 105 to the Pd(0) species. 

---