Formal Oxidation States of Less Than

Lead compounds with a formal oxidation state of less than +2... 

There are a number of solid phases of the types MScCl and ScCl where the formal oxidation state of scandium is less than three. They are usually made by direct combination at elevated temperatures of MCI, ScCl3 and metallic scandium. Their structures often show evidence of Sc—Sc bonds. Thus CsScCl3 is made by action of Sc on Cs3Sc2Cly at 700 °C. The shiny blue product has the hexagonal perovskite CsNiCl3 structure. This is similar to the Cs3Sc2Cl9 structure but with all Sc positions filled. Non-stoichiometric phases exist between the two end structures.128 When scandium is heated with ScCl3 at 940-960 °C in a sealed Ta... 

Through a co-assembling route, mesostructured lamellar molybdenum sulfides are formed hydrothermally at about 85 °C using cationic surfactant molecules as the templates. The reaction temperature and the pH value of the reaction system are important factors that affect the formation of the mesostructured compounds. The amount of the template and that of the S source are less critical in the synthesis of the compounds. For the three as-synthesized mesostructured materials, the interlayer distance increases linearly with the chain length of the surfactant. Infrared and X-ray photoelectron spectroscopy reveals that the individual inorganic layers for the three compounds are essentially the same both in composition and in structure. The formal oxidation state of the molybdenum in the materials is +4 whereas there exist S2 anions and a small amount of (S-S)2 ligands in the mesostructures. The successful synthesis of MoS-L materials indicates that mesostructured compounds can be extended to transition metal sulfides which may exhibit physico-chemical properties more diverse than non-transition metal sulfides because of the ease of the valence variation for a transition metal. 

Electron superconductors, such as Nd2 Ce CuO, do not have oxygen vacancies and the formal oxidation state of copper in these compounds is less than 2. Conduction is by the electron current. 

Example 18-1. For each of the following organometallic molecules, determine the formal oxidation state of the metal, count the total number of valence electrons that the compound has, and justify why any unsaturated compounds have less than 18 valence electrons. 

XAS has been applied to the study of electrolyte side reactions much less often than XPS. Nonetheless, a few examples exist in the hterature of the kind of insight that can be gathered with this tool [189,192,193]. The possibility of collecting data with two different detectors with significantly different, built-in depth sensitivities affords an opportunity to compare the electrode surface with its bulk in a single experiment. Such measurements on layered transition metal oxides revealed a difference in the formal oxidation state of Ni with sample depth that pointed at the active participation of the transition metals in the decomposition of the electrolyte [194]. 

In spite of its great importance, reductive elimination has received less detailed study than oxidative addition. The reaction is most often seen in higher oxidation states, because the formal oxidation state of the metal is reduced by two units in the reaction. The reaction is especially efficient for intermediate oxidation states, such as the d metals, Ni(II), Pd(II), and Au(III), and the d metals, Pt(IV), Pd(IV), Ir(III), and Rh(III). Reductive elimination can also be stimulated by photolysis the case of photoextrusion of H2 from dihydrides is the best known (Section 12.3). 

Cr(CO)sI is isoelectronic with V(CO)6 and like the latter exhibits the expected paramagnetism for a species containing one unpaired electron. Chromium pentacarbonyl iodide appears to be more stable to oxidation but less stable to thermal decomposition than vanadium hexacarbonyl. This higher oxidative stability of Cr(CO)5l as compared with that of V(CO)j may be due to the higher formal oxidation state of the central metal atom of Cr(CO)5l. 

Since the epoxidation step involves no formal change in the oxidation state of the metal catalyst, there is no reason why catalytic activity should be restricted to transition metal complexes. Compounds of nontransition elements which are Lewis acids should also be capable of catalyzing epoxidations. In fact, Se02, which is roughly as acidic as Mo03, catalyzes these reactions.433 It is, however, significantly less active than molybdenum, tungsten, and titanium catalysts. Similarly, boron compounds catalyze these reactions but they are much less effective than molybdenum catalysts 437,438 The low activity of other metal catalysts, such as Th(IV) and Zr(IV) (which are weak oxidants) is attributable to their weak Lewis acidity. 

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