Complexes nonstoichiometric oxides

In addition to the partially oxidized tetracyanoplatinates, bis(oxalato)platinate-(II) can be nonstoichiometrically oxidized by chemical oxidants13 to form highly lustrous needlelike crystals containing platinum in the 2.36 oxidation state. These complexes have not been characterized to the extent of the tetracyano-platinate complexes however, the oxalato complexes are reported to be highly conducting.13 The starting material is bis(oxalato)platinate(II), which can be prepared in 30% yields from hexachloroplatinate(lV) and potassium oxalate.9... 

Specific examples in which results from ALCHEMI are compared with X-ray or neutron diffraction studies on the same sample have been presented for olivine [51], clinopyroxene [57] and feldspar [54] To date, all published planar ALCHEMI studies on mineral samples other than oxides containing high-Z elements (e.g. ceramic nuclear wasteforms, [58]) have been internally consistent and tractable. For example, a combined X-ray diffraction and ALCHEMI study on a complex, nonstoichiometric clinopyroxene [52] has been used to determine the location of vacancies in the structure. In... 

The electrosynthesis, in aqueous solution, of nonstoichiometrically oxidized, highly conducting complexes of platinum has been described,28/27 Eqs. 7.1 and 7.2 ... 

The mechanism of the scaling of iron is so complex as to require special mention. Above 570 °C, wiistite (Fei xO) is thermodynamically stable and forms the relatively thick basal layer in the oxide film. This is followed by a magnetite (FesCU) layer which is followed by a final layer of Fe2C>3. Magnetite itself tends to become nonstoichiometric under oxidizing conditions, with excess Fe3+, so that its composition and color can vary from Fe3.oooC>4 (black) toward cubic Fe2.667 04 (i.e., 7-Fe203, chocolate brown). Thus, as outlined in Section 4.6, the oxidation of iron above 570 °C involves mainly... 

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. 

Carbides and nitrides can be prepared in many ways (chemical vapour deposition, physical vapour deposition, precipitation of salts containing metal, carbon and oxygen followed by reduction and annealing, reaction of a metal or its oxides with a gas or with solid carbon). Carbides and nitrides are often nonstoichiometric with complex phase diagrams.4-9 The compounds sometimes contain multiple phases and impurities, notably oxygen. This can lead to even more complex compounds, like oxycarbides, carbonitrides or oxycarbonitrides. 

The existence of at least nine phases in the molybdenum-oxygen system is well established. Their crystal structures are briefly described and it is shown that they can be classified into four main families dependent on whether they possess a basic structure of rutile type, ReOs type, or MoOs type, or have complex structures where polygonal networks can be distinguished. The known tungsten and mixed molybdenum tungsten oxides fit into this scheme. Because of their complicated formulas many of these compounds may be termed "nonstoichiometric," but variance in composition has not been observed for any of them. 

The formation of nonstoichiometric cation-radical and anion-radical salts can be treated in an analogous manner to the formation of CT complexes. For instance, chemical or electrochemical oxidation of some of the donor molecules in solution leads to the formation of some oxidized molecules, namely cation radicals, which are actually strong acceptors. The latter could easily interact with neutral donor molecules to produce partially positively charged stacks in which the charges are compensated by the counter anions. Such interactions in cation-radical or anion-radical salts could afford nonstoichiometric salts with a formal partial degree of charge transfer, which is determined by the ratio m n in DmX , where X is a counteranion. Representative examples are listed in Table 12. 

This section covers some other heterometallic rare earth oxides, including Al, Ti, Zr, Sn, Mo, W, Mn, Fe, Co, Ni, and Cu complex oxides, while certain well-known oxysalts, Y-Ba-Cu-O, for example, will not be specifically discussed. For these heterometallic compounds, due to their relatively complex compositions, it is usually difficult to obtain phase-pure products, especially when some dopant ions are added. At elevated temperatures, some of these oxides undergo phase transitions, which may significantly change their physical and chemical properties such as thermal expansion coefficient and ionic conductivity. And for fhose oxides with variable metal valencies, different nonstoichiometric compositions may also result in distinct functionalities in magnetism and catalysis. 

Most metal chain complexes involve divalent and partially oxidized square-planar complexes of Ni, Pd, and Pth Examples include the tetracyanoplatinates , bis(oxalato)platinates , bisglyoximato and several complexes containing chelating 7t-conjugated ligands . Nonstoichiometric triplatinum tetraoxides are discussed independently. 

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