Oxides structure types

The transformation of olivine to spinel which delineates the onset of the Transition Zone in the Mantle is isochemical. However, in the Lower Mantle the (Mg,Fe)2Si04 stoichiometry appears to be unstable with respect to denser oxide structure-types. One post-spinel transformation that has been the subject of numerous investigations is the spinel to periclase plus perovskite transition... 

For a review of these and other copper oxide structure types see Muller-Buschbaum, H. Angew. Chem. Int. Ed. 1077, 16, 674. 

Oxide Structure type Unit cell dimensions (A) a 1 c w... 

This process is not as common as the other oxidative procedures and usually involves ring closure onto an aromatic or heteroaromatic ring. The following examples illustrate the structural types required for this cyclocondensation. 

This section considers a number of extremely important structure types in which A1 combines with one or more other metals to form a mixed oxide phase. The most significant of these from both a theoretical and an industrial viewpoint are spinel (MgAl204) and related compounds, Na- -alumina (NaAlnOi ) and related phases, and tricalcium aluminate (Ca3Al20g) which is a major constituent of Portland cement. Each of these compounds raises points of fundamental importance in solid-state chemistry and each possesses properties of crucial significance to... 

The structural features of most niobium oxychlorides known to-date are summarized in Table 6.1. The use of a combination of chloride and oxide hgands leads to compounds with unique structure types [41], characterized by a remarkable variety of cluster frameworks, ranging from discrete cluster units to chains, layers, and three-dimensional nets, some topologies of which are unprecedented in compounds containing octahedral clusters. Most of the niobium oxychlorides known to date have anisotropic structures (the exceptions are Cs2LuNb,5Cli70 and PbLusNbsClisOg). 

By-products from capture of nucleophilic anions may be observed.53 Phenols can be formed under milder conditions by an alternative redox mechanism.98 The reaction is initiated by cuprous oxide, which effects reduction and decomposition to an aryl radical, and is run in the presence of Cu(II) salts. The radical is captured by Cu(II) and converted to the phenol by reductive elimination. This procedure is very rapid and gives good yields of phenols over a range of structural types. 

When the positions of cations and anions are interchanged, the same structure types result for the CsCl, NaCl and zinc blende type. In the case of the fluorite type the interchange also involves an interchange of the coordination numbers, i.e. the anions obtain coordination number 8 and the cations 4. This structure type sometimes is called anti-fluorite type it is known for the alkali metal oxides (Li20,..., Rb20). 

Packings of spheres having occupied tetrahedral and octahedral interstices usually occur if atoms of two different elements are present, one of which prefers tetrahedral coordination, and the other octahedral coordination. This is a common feature among silicates (cf. Section 16.7). Another important structure type of this kind is the spinel type. Spinel is the mineral MgAl204, and generally spinels have the composition AM2X4. Most of them are oxides in addition, there exist sulfides, selenides, halides and pseudohalides. 

The material included in this chapter has been organized by oxidation state, with further subdivision into ligand donor type, and was obtained from reports published in primary research journals. The article will cover coordination complexes of copper in three oxidation states Cum, Cu11, and Cu1. The sections dealing with specific ligand donor types cut across several structural types. In view of the all-inclusive nature of the previous review of CCC(1987), no effort will be made here to present a comprehensive account. Instead, specific cases will be chosen for discussion because they exemplify important concepts concerning the relationship of ligand structure to metal complex properties. 

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