Oxides and other chalcogenides

Oxides and other chalcogenides Table 25.4 Electronic spin-states of iron... 

Many ionic compounds of AX2 stoichiometry possess the CaF2 (fluorite), or Na20 (antifluorite) structures shown in Figure 3.15. Fluorite is similar to CsCl, but with every other eight coordinate cation removed. Each fluoride anion is tetrahedrally coordinated by calcium ions. This structure is adopted by several fluorides and oxides. In the antifluorite structure, the coordination numbers are the inverse. Most oxides and other chalcogenides of the alkali metals (e.g. Na2Se, K2Se) possess the antifluorite structure, but so do some more covalent compounds, such as the silicides of Mg, Ge, Sn, and Pb. 

Like the oxides, sulfides, and other chalcogenides are mostly based structurally on a tetrahedral array of P or As atoms with bridging S or Se atoms and, less commonly, terminal S or Se, but the details differ a good deal. We shall discuss in detail only the phosphorus sulfides. Some of the known structures are shown in Fig. 10-11. Some are known quantitatively from X-ray crystallography, but for others only the qualitative structure is available from 31P nmr. At least four more, including two forms of P4Sg, are known. 

There are comparatively few data available for iron sulphides and other chalcogenides, though interesting comparisons can be made in those cases where there are equivalent oxide systems. The same broad trends in the Mossbauer systematics are observed. Thus for chemical isomer shifts... 

Solvothermal Process Precipitation fi"om a nonaqueous solution of precursor salts under high temperature. Application of high pressure is optional Particle size control By reaction temperature and duration, precursor concentration, pH, surfactant additive, precursor materials, and solvent General attributes High crystallinity spherical shapes as well as unique morphologies not only oxides but also sulfides and other chalcogenide compounds... 

Weitkamp J, Rymsa U, Wark M, Schulz-Ekloff G (2002) Preparation of Oxide, Sulfide and Other Chalcogenide Clusters in Molecular Sieves. 3 339-414 Weitkamp J, see TraaY (2006) 5 103-154 Werthmann U, see Gies H (1998) 1 35-64... 

Wilson and coworkers assessed the performance of 13 hybrid-GGA, hybrid-meta-GGA, and double-hybrid DFT functionals on the cc-CA-TM/11 dataset [83]. The hybrid B97-1 [42, 84] functional and the double-hybrid functional mPW2-PLYP [85] were found to give the best performance over experimental results with mean absolute deviations of 7.2 and 7.3 kcal mol . The dataset (cc-CA-TM/11) is rather diverse and consists of AyH of 193 3d transition metal molecules (Sc(C5H5)3 and (Cr03)3, halides, oxides, and heavy chalcogenides, hydrides, nitrides, small clusters, metal carbonyls, and other coordination complexes) [86]. 

Preparation of Oxide, Sulfide and Other Chalcogenide Clusters in Molecular Sieves... 

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