Coordination chemistry hydroxides

The fact that tantalum and niobium complexes form in fluoride solutions not only supplements fundamental data on the coordination chemistry of fluoride compounds, but also has a broad practical importance. This type of solution is widely used in the technology of tantalum and niobium compounds in raw material digestion, liquid-liquid extraction, precipitation and re-pulping of hydroxides, and in the crystallization and re-crystallization of K-salts and other complex fluoride compounds. 

Malonic acid CH2(C02H)2 (H2mal) (209) has a coordination chemistry with chrommm(III) closely resembling that of oxalate. Malonic acid is a slightly weaker acid than oxalic acid and slightly more labile complexes are formed. The tris complex is the most extensively studied, prepared by the reduction of chromate solutions or the reaction of chromium(III) hydroxide with malonate.917,918 919 The cis and trans diaqua complexes may be prepared by the reduction of chromate with malonate the isomers are separated by fractional crystallization. The electronic spectrum of the tris complex is similar to that of the tris oxalate and a detailed analysis of these spectra has appeared.889... 

The reaction of secondary diamines, carbon disulfide, and alkali metal hydroxides gives bisdithiocarbamate salts, which, upon reaction with bischloro-methylated aromatics, afford soluble polydithiocarbamates (392). The coordination chemistry of these polymers should be investigated. They may prove to be interesting, and, perhaps, specific, metal-sequestering agents. 

The coordination chemistry of sea water represents a new and useful approach to understanding the chemical properties of sea water. The coordination chemistry of sea water differs from contemporary coordination chemistry in the following respects most complexes involve pretransition metals, most complexes are labile, the ligands are simpler (water, hydroxide, chloride, carbonate, sulfate), and time and space are important parameters. Principles of coordination chemistry are applied to contemporary research in marine science in four areas analysis of constituents of natural waters, the nature of metallic species in the oceans, the Red Tide problem, and carbonate geochemistry. 

Aluminum occurs widely in nature in silicates such as micas and feldspars, complexed with sodium and fluorine as cryolite, and in bauxite rock, which is composed of hydrous aluminum oxides, aluminum hydroxides, and impurities such as free silica (Cotton and Wilkinson 1988). Because of its reactivity, aluminum is not found as a free metal in nature (Bodek et al. 1988). Aluminum exhibits only one oxidation state (+3) in its compounds and its behavior in the environment is strongly influenced by its coordination chemistry. Aluminum partitions between solid and liquid phases by reacting and complexing with water molecules and anions such as chloride, fluoride, sulfate, nitrate, phosphate, and negatively charged functional groups on humic materials and clay. 

A detailed model for the oxygen reduction reaction at semiconductor oxide electrodes has been developed by Presnov and Trunov [341, 345, 346] based on concepts of coordination chemistry and local interaction of surface cation d-electrons at the oxide surface with HO, H20, and 02 acceptor species in solution. The oxygen reduction reaction is assumed to take place at active sites associated with cations at the oxide surface in a higher oxidation state. These cations would act as donor-acceptor reduction (DAR) sites, with acceptor character with respect to the solid by capture of electrons and donor electronic properties with respect to species in solution. At the surface, the long-range oxide structure is lost and short-range coordination by hydroxide ions and water molecules in three octahedral positions may occur [Fig. 16(b)], One hydroxide ion can compensate coulombically for the excess charge on surface M2+ cations with two coordinated water mole-... 

Coordination Chemistry of Rare Earth Alkoxides, Aryloxides, and Hydroxides... 

The large number of lanthanide alkoxide complexes featuring the inclusion of oxo or hydroxo groups unmistakably suggests that the coordination chemistry of lanthanide hydroxide is intimately associated with that of the alkoxides. Arguably the simplest and most ubiquitous O-containing ligand, the water molecule, occupies a special position in the development of lanthanide coordination chemistry. Upon coordination to the Lewis acidic lanthanide ion, an... 

The octanuclear lanthanide hydroxide cluster core was first identified in Er8( X4-0)( X3-OH)i2(THD)s (THD = 2,2,6,6-tetramethyUieptane-3,5-dionate) [25, 87]. It is a triangulated dodecahedron with an interstitial oxo group each of its triangular faces is capped by a IX3-OH group. The same cluster core has also been found in [Eu8(p-6-0)((i,3-0H)i2( X2-0Tf)i6(0Tf)2] (Eigure 6.40) [99] and [Eu8( X4-0)((i,3-0H)i2(DME)8(Se3)(Se4)3(Se5)2] [105]. That the same cluster core is obtained with different ancillary ligands suggests the prevalence of this motif in the lanthanide hydroxide coordination chemistry. 

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