Solid decompositions, isomorphic

Each crystalline substance has a unique structure. Groups of compounds classified as isomorphous have similarities of lattice symmetry, but dimensions, and hence interionic forces, are different. Moreover, a particular substance can adopt alternative structures under changed conditions of temperature, pressure, crystallization conditions, presence of impurities, etc. Ordered packing, with symmetrical intracrystalline forces, appears to confer enhanced stability within the bulk solid so that decomposition processes usually occur at surfaces within a restricted reaction zone. Interfaces can be regarded variously as complex imperfections, zones of destabilizing strain, or (product) sites of catalytic activity. 

Triruthenium dodecacarbonyl (Ru3(CO)i2) orange solid, was first (276) prepared by decomposition of Ru(CO)5 but initially incorrectly identified as Ru2(CO)g. This error was first rectified in 1961 when Ru3(CO)i2 was shown (87) to be isomorphous to OS3(CO)i2 and the crystal structure of the latter was determined by x-ray diffraction. Later the structure of Ru3(CO)i2 was determined to be 11 (M = Ru) with the ruthenium triangle having 2.85-A edges (282). In 1966 (48, 50) an improved preparation of Ru3(CO)i2 was developed, utilizing the reductive carbonylation of hydrated ruthenium(III) chloride with carbon monoxide at 10-atm pressure in the presence of zinc, according to the following reaction ... 

There are known cases when formation of a solid solution actually removes the valence tension in the structure and stabilizes a state in which an individual compound does not exist. Thus, pure CuF is unstable against decomposition into elemental Cu and CuFa, but is quite stable as an isomorphic impurity (up to 2 %) in NaF, where A c(Cu+) = 6 according to spectroscopic data [97], although crystal-chemical rules suggest that CuF should belong to the structural type of ZnS. 

Dimethylsilanediol is a crystalline solid (m. p. 100-101 °C)which is highly sensitive to traces of acid or base. It is best prepared by slow hydrolysis of dimethyldimethoxy-silane. In contrast, di-t-butylsilanediol (m. p. 152 °C) can be distilled at 210°C without decomposition, and it is unaffected by hot, concentrated sulphuric acid [211], although condensation will occur in the presence of p-toluenesulphonic acid [212]. Some organosilanediols are isomorphous. 

Mixed oxides derived from thermal decomposition of LDHs have acid-base properties that influence the catalytic behavior of these materials and depend on the molar ratio Mii/m" ions, their diameters, charge, calcination temperature, and synthesis methods [50, 51]. The acid-base centers are highly active centers that participate in numerous reactions. These properties can be modified by the variation of the M /M molar ratio, by isomorph substitution of a part of M that are present in the structure with other divalent metal ions (such as NT, Be, Co, Zn +, Cu +, Mn +, Cr +, and Fe " ) and by isomorph substitution of a part of M" that are present in the structure with other trivalent metal ions (e.g. Ga T Fe T Co T NTT Mn T V T In T Rh T Ru ") [2]. With the increase of the M cation presence the amount of acid centers also increases in mixed oxides. Acidity depends on the nature of the M cations, for instance AP+ cations exhibit higher acidity than Fe +cations [1]. After thermal decomposition of LDHs, mixed oxides are formed that present solid bases. The alkalinity level depends on the synthesis method. Application of the coprecipitation and sol-gel methods leads to the formation of mixed oxides that have base centers of Lewis type with medium strength... 

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