X-type ions

The polyhalide ions may convenienlly be classiiied into two groups (X) -type ions belong to both groups) (I) those that are isoelectronic with noble gas compounds and... 

The 2eohte sodium X (type 13X) has a crystallographic aperture of 0.74 nm. This compares well with the adsorbate value of 0.81 nm. ZeoHte calcium X exhibits a smaller apparent pore si2e of 0.78 nm (lOX). This difference is probably due to some distortion of the aluminosihcate framework upon dehydration and calcium ion migration. 

One type of point defect that cannot be entirely eliminated from a solid compound is the substituted ion or impurity defect. For example, suppose a large crystal contains 1 mole of NaCl that is 99.99 mole percent pure and that the 0.01% impurity is KBr. As a fraction, there is 0.0001 mole of both K+ and Br ions, which is 6.02 X 1019 ions of each type present in the 1 mole of NaCl Although the level of purity of the NaCl is high, there is an enormous number of impurity ions that occupy sites in the lattice. Even if the NaCl were 99.9999 mole percent pure, there would still be 6.02 X 1017 impurity cations and anions in a mole of crystal. In other words, there is a defect, known as a substituted ion or impurity defect, at each point in the crystal where some ion other than Na+ or Cl- resides. Because K+ is larger than Na+ and Br is larger than Cl-, the lattice will experience some strain and distortion at the sites where the larger cations and anions reside. These strain points are frequently reactive sites in a crystal. 

There are two identical BR-type sites in the unit cell to accommodate the 1 + x Na+ ions, and there are always vacant BR-type sites in proximity to occupied sites. When cations of higher valence replace sodium, the number of vacant BR-type sites increase in proportion. Although there is no geometrical reason why large cations should occupy other sites, in many compounds, the large cations are located in both BR-type sites and mO sites. As in the case of (3-alumina, the defect structure of each compound is uniquely related to the chemical nature of the cations in the conduction layer. 

A carbocation is strongly stabilized by an X substituent (Figure 7.1a) through a -type interaction which also involves partial delocalization of the nonbonded electron pair of X to the formally electron-deficient center. At the same time, the LUMO is elevated, reducing the reactivity of the electron-deficient center toward attack by nucleophiles. The effects of substitution are cumulative. Thus, the more X -type substituents there are, the more thermodynamically stable is the cation and the less reactive it is as a Lewis acid. As an extreme example, guanidinium ion, which may be written as [C(NH2)3]+, is stable in water. Species of the type [— ( ) ]1 are common intermediates in acyl hydrolysis reactions. Even cations stabilized by fluorine have been reported and recently studied theoretically [127]. 

The -nitrido-bis(triphenylphosphorus)(l+) ion,2-4 [ (C6H5)3P 2N]+,is one of the most convenient counterions for such purposes. Compounds of the [ (C6H5)3P 2N][X] type are soluble in most commonly used organic solvents. They also often form good-quality single crystals, suitable for X-ray diffraction analysis. 

TOFSIMS analyses were performed on a Kratos PRISM instrument. It was equipped with a reflectron-type time-of-flight mass analyzer and a pulsed 25 kV liquid metal ion source of monoisotopic 69Ga ions with a minimum beam size of 500 A. Positive and negative spectra were obtained at a primary energy of 25 keV, a pulse width of 10-50 ns, and a total integrated ion dose of about 10" ions/cm2. This is well below the generally accepted upper limit of 5 x 1012 ions/cm2 for static SIMS conditions in the analysis of organic materials [12], The mass resolution at mass 50 amu varied from M/AM= 1000 at 50 ns pulse width to about 2500 at 10 ns pulse width. 

Following the accepted assignments for PDMS [17], the ions with mass at m/z = 120 and 239 were readily assigned to an analogous linear form for HAPS (ii) with w = 0 and 1, which corresponds to s = 0 and 1 (i). The ion at m/z =221 was considered to arise from a cyclic structure of x type (iii) with x = 0. Ions with more than two structural repeat units were not observed. 

A typical reaction of halide ions is their combination with a halogen molecule X2 to give the linear trihalide ions. In accord with its postulated pseudohalide character, the dicyanophosphide ion adds bromine and iodine at room temperature to give anions of X type with PCCN as central member. The crown ether-sodium salts of these hypervalent anions, dicyanodihalophosphates (III), can be isolated in crystalline form. 

The 6 x 1022 particles leaving the 6 GW(t) reactor per second carry 150 MW of power. With approximately 5 x 101 m2 of trapping surface (some 10% of the reactor vacuum wall area), the power loading becomes 3 x 106 Wm 2. The maximum ion current density which has to be considered is — 1 x 1021 ions m 2s 1 or 1.9 x 10s mA m-2. Such ion current densities incidentally are experimentally accessible with ion sources of the duoplasmatron type. 

Primary Shape Selectivity. There are several types of shape and size selectivity in zeolites. First, the reactant molecules may be too large to enter the cavities. A particularly good illustration of this behavior is given by Weisz and co-workers (5). Zeolites A and X were ion exchanged with calcium salts to create acid sites within the zeolite. These acid sites are formed as the water of hydration around the calcium ions hydrolyzes. When these zeolites are contacted with primary and secondary alcohols in the vapor phase, both alcohols dehydrate on CaX but only the primary one reacts on CaA. Since the secondary alcohol is too large to diffuse through the pores of CaA, it can not reach the active sites within the CaA crystals. This kind of selectivity is called reactant shape selectivity and is illustrated in Figure 3. 

Another example is provided by a series of octahedral MX Y6 type ions (n = 0-6), where M is Pt(IV), Os(IV), and Ir(IV), and X and Y are halogens. Preetz and co-workers (4) prepared these mixed-halogeno ions and assigned their IR/Raman bands based on point group symmetry. Table 4-3 shows the point group and classification of IR/Raman-active fundamental vibrations. Figure 4-3 shows the IR/Raman spectra and band assignments of the [PtCl Br6 ]2 series. It should be noted that these ions exhibit v(PtCl),... 

X-type Contains the oxide ions in hexagonal arrangements. 

For example, VoTKhin et al. [121] have prepated manganese oxide in spinel type, by exchanging proton for lithium ions in manganese oxide containing lithium ions. Similar results were obtained with the X-type MnOz [34,122]. These oxides showed an extremely high selectivity for... 

To summarize, one may use the Scandinavian type accelerator for the production of ions of all elements with energies up to a few hundred keV and intensities of 10 nA(6 X 10 ions/sec) or the Harwell type for intensities of 100 iiA (6 X 10 ions/sec). There are also a number ofother constructions which differ to some extent from the types mentioned. Multistage accelerators, for instance, deliver ions with energies up to 10 MeV/A (MeV/nudeon) with intensities 10 ions/sec. 

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