Cations structure

Every ionic crystal can formally be regarded as a mutually interconnected composite of two distinct structures cationic sublattice and anionic sublattice, which may or may not have identical symmetry. Silver iodide exhibits two structures thermodynamically stable below 146°C sphalerite (below 137°C) and wurtzite (137-146°C), with a plane-centred I- sublattice. This changes into a body-centred one at 146°C, and it persists up to the melting point of Agl (555°C). On the other hand, the Ag+ sub-lattice is much less stable it collapses at the phase transition temperature (146°C) into a highly disordered, liquid-like system, in which the Ag+ ions are easily mobile over all the 42 theoretically available interstitial sites in the I-sub-lattice. This system shows an Ag+ conductivity of 1.31 S/cm at 146°C (the regular wurtzite modification of Agl has an ionic conductivity of about 10-3 S/cm at this temperature). 

Clay minerals behave like Bronsted acids, donating protons, or as Lewis acids (Sect. 6.3), accepting electron pairs. Catalytic reactions on clay surfaces involve surface Bronsted and Lewis acidity and the hydrolysis of organic molecules, which is affected by the type of clay and the clay-saturating cation involved in the reaction. Dissociation of water molecules coordinated to surface, clay-bound cations contributes to the formation active protons, which is expressed as a Bronsted acidity. This process is affected by the clay hydration status, the polarizing power of the surface bond, and structural cations on mineral colloids (Mortland 1970, 1986). On the other hand, ions such as A1 and Fe, which are exposed at the edge of mineral clay coUoids, induce the formation of Lewis acidity (McBride 1994). 

Paramasivan S, Rujan I, Bolton PH (2007) Circular dichroism of quadruplex DNAs Applications to structure, catione effects and ligand binding. Methods 43 324-331... 

Cathodic Protection method where a more active metal is connected to a metal structure such as a tank or a ship protecting the structure because the active metal is oxidized rather than the structure Cation a positively charged ion Cellulase a group of enzymes that hydrolyze cellulose... 

Under a variety of conditions, plasmid DNA undergoes a dramatic compaction in the presence of condensing agents such as multivalent cations and cationic polymers. Naked DNA coils, typically with a hydrodynamic size of hundreds of nanometers, after condensation it may become only tens of nanometer in size. Contrary to proteins which show a unique tertiary structure, DNA coils do not condense into unique compact structure. Cationic polymers execute their gene carrier function by their condensation effect on gene materials and, furthermore, their protection effect on DNA from nuclease digestion. Currently, the most widely used cationic polymers in research include linear or branched PEI (poly (ethyleneimine) (161-165), polypeptides such as PLL (poly-L-lysine) (166-169), PLA (poly-L-arginine) (170). 

Figure 12. Supercage structure, cation location (I, II, III or 1, 2, 3) within X- and Y-type zeolites. Bottom portion shows the reduction in available space (relative) within the supercage as the cation size increases.

The groups of Kobayashi and Underhill have focused their attention on partially oxidized Ni and Pt mnt complex anions with nonstoichiometric proportions of different cations. Such nonintegral valence salts have the general structure (cation), M(mnt)" (H2 0)x (x = 0-2), in which n can be anywhere between 0.5 and 0.82. 

Specific electrolyte adsorption can occur on oxides by ion exchange with structural cations, with hydrogen or hydroxyl of the surface hydroxide groups, or with impurities (92, 94). Ions which can form insoluble compounds or undissociated complexes with a component of the solid crystal lattice adsorb more strongly than those which cannot (2). This does not imply or require that such complexes or compounds do or do not form. The question may be left open. It does imply that, of a series of species which form insoluble compounds with components of the solid, that which forms the least-soluble compound will be adsorbed most strongly. Thus any generalization which can be used to predict solubility or complexing tendency can be extended to predict adsorba-bility, at least qualitatively. 

Feigenbaum, S., Edelstein, R., and Shainberg, I. (1981). Release rate of potassium and structural cations from micas to ion exchangers in dilute solutions. Soil Sci. Soc. Am. J. 45, 501-506. 

Many ferroelectric materials were found in the past. However, there is a limited number of structures that are adopted by the majority of the commercially important ferroelectric materials. In each of these structures, the ferroelectricity is tied to distortion of the coordination polyhedra of one or more of the cations in the structure. One example is the perovskite structure. Cations that seem to be especially susceptible to forming such distorted polyhedra include Ti, Zr, Nb, Ta, and Hf. All of these ions lie near crossover points between the stability of different electronic orbitals, and so may be likely to form distorted coordination polyhedra [5], Polarizable cations such as Pb and Bi are also common to many ferroelectric materials. In this case, it has been suggested that the lone pair electrons may play an important role in stabilizing ferroelectric structures. Thus the ferroelectric transition temperature and spontaneous distortion of PbTiC>3 is much larger than that of BaTiC>3. 

C1206 is actually a mixed-valence ionic compound ClOtCIO, in which the angular CIO and tetrahedral CIOJ ions are arranged in a distorted CsCl-type crystal structure. Cation ClOj has Cl-O 141 pm, angle O-Cl-O 119° CIOJ... 

Electronic Structure Cation Electronic configuration A corundum (cm-1) A periclase (cm-1) A aqueous (cm-1) CFSE of hexahydrate Pairing energy (cm-1)... 

Electronic structure Cation Electronic configuration Octahedron elongated along tetrad axis Octahedron compressed along tetrad axis Configuration of the most stable six-coordinated site... 

Electronic structure Cation Electronic configuration sa octahedral tetrahedral ASel (oct - tet) J/(deg.mole) ASel (Is—hs) J/(deg.mole)... 

Mineral (structure) Cation Site Ko (spectral) (GPa) Spectral data sources KqX (X-ray) (GPa) X-ray data sources 0 (bulk crystal) (GPa) Bulk moduli sources... 

Sawamoto, H. Horiuchi, H. (1990) (HMgojFeg,)2Si04 Single crystal structure, cation distribution, and properties of coordination polyhedra. Phys. Chem. Minerals, 17, 293—300. 

HfaS and HfaSe crystallize in the anti-structure, cations and anions being interchanged. 

The net permanent structural surface charge density, denoted gq and measured in coulombs per square meter (C/m2), is created by isomorphic substitutions in minerals [4]. These substitutions in clay minerals produce significant surface charge only in the 2 1 layer types. In these minerals, Co < 0 invariably because of structural cation substitutions. The relation between gq and the layer charge jc is [3]... 

A weak 2kF diffuse x-ray scattering [58], seen only at low temperature, confirms that p = in this salt and indicates that the Fermi wave vector is rather well defined despite structural cation disorder. A stronger 4kF scattering [58] observed from 25 K to 300 K is an indication of large Coulomb effects in this salt, with U t, in agreement with other known magnetic and thermopower data [57,58]. 

Since the various 2- and 3-octyl cations will be in rapid equilibrium, the data in this Table are referenced to the most stable ground-state structure, cation 23. 

Structure Cation Typical formula of unit cell or pseudocell Window Effective channel diameter, mn Applications... 

In the perovskite structure, cations in site A have coordination number 12, whereas those in site B have coordination number six. See Figure 3.42 for more information on the perovskite structure. 

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