Oxygen, solid crystal structure

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and tlreh oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, fenites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

Figure 1. The crystal structure of Zr2(0H)2(SO4)3(H2O)4> reprinted with permission from Ref. 5, copyright 1966, American Chemical Society. Zirconium atoms are shown as solid circles, oxygen atoms as open circles. The Pu compound is isomorphous, Zr being replaced by Pu. la shows the manner in which the bridging sulfates link Pu atoms to form layers, lb shows the manner in which layers are linked through the double hydroxide bridges.

Although the band model explains well various electronic properties of metal oxides, there are also systems where it fails, presumably because of neglecting electronic correlations within the solid. Therefore, J. B. Good-enough presented alternative criteria derived from the crystal structure, symmetry of orbitals and type of chemical bonding between metal and oxygen. This semiempirical model elucidates and predicts electrical properties of simple oxides and also of more complicated oxidic materials, such as bronzes, spinels, perowskites, etc. 

Fig. 4. Diagrammatic representation of layered crystal structures of rigid diols, with closed hydrogen bonding cycles. Open circles are oxygen atoms, filled circles hydrogen atoms, and the solid lines represent the connecting diol. Hydrogen bonds are shown as broken lines, (a) The structure of 2,6-dihydroxy-2,6-dimethyltricyclo[3.3.1.13,7]decane (4). (b) The structure of erafo-2,e do-6-dihydroxy-2,6-dimethylbicyclo[3.3.1]nonane, (7)...

A number of chemical elements, mainly oxygen and carbon but also others, such as tin, phosphorus, and sulfur, occur naturally in more than one form. The various forms differ from one another in their physical properties and also, less frequently, in some of their chemical properties. The characteristic of some elements to exist in two or more modifications is known as allotropy, and the different modifications of each element are known as its allotropes. The phenomenon of allotropy is generally attributed to dissimilarities in the way the component atoms bond to each other in each allotrope either variation in the number of atoms bonded to form a molecule, as in the allotropes oxygen and ozone, or to differences in the crystal structure of solids such as graphite and diamond, the allotropes of carbon. 

The interaction of beryllium with nitrilotripropionic acid (H3ntp) has been investigated in some detail (244). This acid forms a strong complex (log Kt = 9.24) that can be isolated as a solid. The crystal structure of the anion [Be(ntp)] is shown in Fig. 23. The structure confirms the coordination of the nitrogen atom along with an oxygen atom from each carboxyl group. 

Isotope fractionations in solids depend on the nature of the bonds between atoms of an element and the nearest atoms in the crystal structure (O Neil 1986). The correlation between bond strength and oxygen isotope fractionation was investigated by Schiitze (1980), who developed an increment method for predicting oxygen isotope fractionations in silicate minerals. Richter and Hoemes (1988) applied this method to the calculation of oxygen isotope fractionations between silicate minerals and... 

How can we be sure that the U +(Q2-) complex in a mixed metal oxide is present as the UO octahedron This can be done by studying solid solution series between tungstates (tellurates, etc.) and uranates which are isomorphous and whose crystal structure is known. Illustrative examples are solid solution series with ordered perovskite structure A2BWi aUa 06 and A2BTei-a Ua 06 91). Here A and B are alkahne-earth ions. The hexavalent ions occupy octahedral positions as can be shown by infrared and Raman analysis 92, 93). Usually no accurate determinations of the crystallographic anion parameters are available, because this can only be done by neutron diffraction [see however Ref. (P4)]. Vibrational spectroscopy is then a simple tool to determine the site symmetry of the uranate complex in the lattice, if these groups do not have oxygen ions in common. In the perovskite structure this requirement is fulfilled. 

The sodium and potassium salts of 11 and 12 and their hydrates have been synthesized and characterized . The solid state structures of anhydrous potassium salt of 12 and its hydrate have been determined by single-crystal X-ray diffraction (Figure 21). Each structure has nearly planar N2O2 groups arranged as blades of a propeller around the main C-H axis. The three blades have similar helicities, or relative orientations. Helicity can be viewed as the relative orientation of the oxygen of the carbon-bound nitrogen with respect to the plane defined by the HCN atoms for the individual blades . ... 

Thermodynamically, we would like to know which material minimizes the free energy of a system containing gaseous 02 and a solid at the specified conditions. A useful way to do this is to define the grand potential associated with each crystal structure. The grand potential for a metal oxide containing NM metal atoms and No oxygen atoms is defined by... 

Information about the electronic structure of the 4,5-dimethoxy-o-quinodimethane adduct 46 in the solid state, prepared from 6,7-dimethoxy-3-isochromanone 42 (Rj = R4 = H R2 = R3 = OMe), comes from ESCA measurements [43]. In accord with the crystal structure analysis [43, 58], this cycloadduct, which contains the electron-rich dimethoxyphenyl moiety, shows an intermolecular donor-acceptor interaction, in particular, of the methoxy oxygen to the unit. 

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