Idealized structural formulas

Table I. Idealized Structural Formulae for Principal Smectite Clays...

P-tetragonal structure group (idealized structure formula (B2r2Bi2)4(XmY )) missing or incomplete occupation of X,Y sites, two missing B sites in B21 double-icosahedra (Bi9 in a-AlBi2) (210). 

Table I. Idealized structural formulae for principal smectite clays.

The total potassium contents of illites are lower than those of true micas. Illite contents of soils are often calculated from the chemical analysis of bulk clay samples by assuming potassium contents of 5 to 8% in contrast to theoretical values of 9.8, 7.6, and 9.4%, which follow from the ideal structural formulas of muscovite, biotite, and phlogopite, respectively. 

Beidellite is characterized by tetrahedral replacements. The idealized structural formula is written as... 

Stevensite (Faust et al. [1959]) belongs to the first category that is, the negative charges do not come from isomorphous replacements, but are created by atom vacancies in the octahedral layer. The idealized structural formula (neglecting minor replacements) is written as... 

Following the obvious parallels with p-block hybridization and bonding, the formation of a duodectet-rule-conforming Lewis-like structural formula for an idealized ML transition-metal complex5 can be pictured as occurring in several steps. 

The parent perovskite-type structure (Fig. 4.13A>) is composed of corner-linked BOe octahedra surrounding large A cations and is conveniently idealized to cubic symmetry (Fig. 4.27a). (The real structures have lower symmetry than the idealized structures, mainly due to temperature-sensitive distortions of the BOft octahedra.) In the phases related to Ca2Nb2C>7 the parent structure is broken into slabs parallel to 110 planes. The formula of each slab is A B 03 +2, where n is the number of... 

In the materials that follow, the structures are all layered. This structural feature has lead to a description of the doping in terms of charge reservoirs, a different approach to that described previously, and which is detailed below. Structurally the phases are all related to the perovskite-layered structures (Figs. 4.27, 4.28, 4.29, and 4.30). The similarity can be appreciated by comparison of the idealized structures and formulas of some of these materials, Bi2Sr2CuOg... 

The site and its occupancy are represented by two right lower indexes separated by a comma. The first index indicates the type of site the second one indicates the number of atoms in this site. (Aa, for instance, means an atom A on a site occupied by A in the ideal structure, whereas AB represents an atom A in a site normally (ideally) occupied by B). A formula such as MM)1 x v or (Mi 1 Jv represents a disordered alloy, whereas... 

Some chemical compounds exist in more than one structural form. For example, the idealized chemical formula for both of the mineral species chrys-... 

Oxides of the formula A B 03 +2 fomi a large family in which A is an alkaline earth and/or a lanthanide ion and B is titanium and/or nobium. Different members of this series are found in A2Nb207 CaTi03 (A = Ca, Sr) and Ln2Ti207 CaTi03 (Ln = La, Nd) systems. The ideal structure is orthorhombic, but monoclinic distortion often... 

Many of the complexes which occur in spin equilibrium possess ligands with complicated structures. Trivial abbreviations are used, with structural formulas given in the table in which the complex first appears. Generally the complexes are of low symmetry, but in the description of their electronic structure idealized symmetries are assumed and the appropriate term symbols are used accordingly. 

Ideally, every organic substance should have a completely descriptive, systematic name to permit only one structural formula to be written for it. This ideal has been approached closely in some of the current nomenclature systems but, unfortunately, truly systematic nomenclature for very complicated compounds is often hopeless for conversational or routine scripto-rial purposes. As a result, we will at times resort to using (common) trivial names, especially if it is impractical to do otherwise. Clearly, the description 9-(2,6,6-trimethyl-l-cyclohexenyl)-3,7-dimethyl-2,4,6,8-nonatetraen-J-ol has phonetic disadvantages as a handy name for vitamin A ... 

There is a family of compounds known as Chevrel phases (Roger Chevrel, 1971) with the general formula MxMo6Xs, where M represents a rare earth metal, a transition or main group metal, and possibly a vacancy X can be S, Se, or Te. The idealized structure of PbMoftSs is... 

Armbruster [14]. The structure of 14A-Tobermorite (equivalent to the CSH cement phase) is usually inferred from that of 11 A-Tobermorite and its ideal chemical formula is Ca22XSifi., pH %H20. The primary structural unit of Tobermorite contains CaO polyhedral sheets sandwiched between single silicate chains. The silicate chains are based on a three units repeating pattern called dreierketten arrangement of 7.8A in length in which two of the tetrahedra point toward the CaO polyhedral sheet while the third points toward the interlayer void. 

The product is a white powder and very sensitive to moisture. The given structural formula is idealized, because most likely, extensive cross-linking occurs through reactions involving NH2 and SiH groups. The cross-linked... 

Titanates and titanoniobates of the general formula A2-vTi vNbv02 +1 (A = alkali metal) crystallize in layered structures possessing [Ti , vNbv02 +i sheets stacked with interlayer A ions [1, 2]. The sheets may be obtained from edge-connected layers of double-ReOr units by shearing every n-octahedron perpendicular to the sheets. Idealized structures of some of these oxides are shown in Figure 1. Several oxides in this family are known to exhibit interlayer chemistry... 

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