Aluminum solute complexes, structure

As discussed above, the presence of AI13 is usually identified via a +62.5 ppm peak in the Al-NMR spectra that arises from the central Al(0)4 site in the s-Keggin-like AI13 structure. Fu et al. (1991) and Nazar et al. (1992) noticed that additional peaks for the A1(0)4 occur in the Al-NMR spectra when AI13 solutions were reacted for extended periods of time at temperatures of 85-90°C and polymerized by titration with base. Peaks in the Al-NMR spectra appear at +64.5, +70.2, and +75.6 ppm as a peak near 0 ppm increases in intensity. The 0 ppm >eak arises from the monomeric aluminum hydrolysis complexes, mostly Al + Al(OH) at 4 < pH < 5. The peak at +64.5 ppm is weak and transient and that at 75.6 ppm only appears after extended periods of reaction. The dominant peak is at 70.2 ppm. 

Jordan PA, Clay den NJ, Heath SL, Moore GR, Powell AK, Tapparo A (1996) Defining speciation profiles of Al complexed with small organic ligands the Al -heidi system. Coord Chem Rev 149 281-309 Karlsson M (1998) Structure studies of aluminum(III) complexes in solids, in solutions, and at the solid/water interface. PhD thesis. University of Umea... 

Lothenbach B, Furrer G, Schulin R (1997) Immobilization of heavy metals by polynuclear aluminum and montmorillonite compounds. Environ Sci Technol 31 1452-1462 Marklund E, Ohman L-O (1990) Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 24 A potentiometric and Al NMR study of polynuclear aluminum(III) hydroxo complexes with lactic acid. Acta Chem Scand 44 228-234 Matzapetakis M, Raptopoulou CP, Terzis A, Lakatos A, Kiss T, Salifoglou A (1999) Synthesis, structural characterization, and solution behavior of the first mononuclear, aqueous aluminum citrate complex. Inorg Chem 38 618-619... 

Lewinski and coworkers recently used this reaction sequence and achieved full characterization of the aluminum-peroxide complex by X-ray single-crystal analysis (Scheme 6.143) [183]. The structure is consistent wifh a mixture of tetra- and hexacoordination and wifh solution spectroscopic data. Unlike fhe usual instabihty of alkylperoxide complexes of aluminum, this peroxo complex is relatively stable, partly because of the hexacoordination also because of fhe steric bulk of fhe t-Bu groups attached to oxygen atoms. 

A. (1998). Synthesis, structural characterization, and solution behavior of the first mononuclear, aqueous aluminum citrate complex. Inorg. Chem. 38, 618-619. 

In several of the studies of aqueous chemistry of aluminum that have been made since about 1950, polynuclear complexing mechanisms have been proposed to identify and describe the dissolved aluminum hydroxide complex species (3, JO, 11). The formulae proposed have generally been based on stoichiometric considerations and pH measurements assuming the polynuclear species were ionic, and that equilibrium was attained. The complex ions reported by Hsu and Bates (8) were single six-mem-bered rings Ale (OH) 12 or multiples of this unit. Johansson (JO) identified a structural unit containing 13 aluminum and 40 oxygen atoms with various numbers of protons in crystalline basic aluminum sulfate. Because this solid formed readily, the same structural unit of aluminum was proposed as a solute species. Most of the proposed formulae for polynuclear complexes, however, have not been derived from structural considerations. 

The aqueous speciation of Si " is fundamentally different from that of Al in water at low temperature. Whereas aluminum is octahedrally coordinated with water and/or hydroxide, silicon is tetrahedrally coordinated by hydroxide only, with no coordinating water. In contrast to alumina Al(0H)n(H20)3 , the hydroxyls on Si(OH)4 (Fig. 8) participate in hydrogen-bonding interactions with water and with each other, creating a complex structure in solution and making it impossible to isolate pure monomeric Si(OH)4 (Her 1979). Also, the silica hydroxyl hydrogens are much less acidic than the hydrogens associated with coordinated water on... 

The results of the reductions of some steroidal a,)3-unsaturated ketones have been summarized by Brown. " The carbonyl group is usually reduced to the hydrocarbon, but the behavior of the double bond depends on the structure of the compound undergoing the reduction. Cholest-4-en-3-one gives chol-est-4-ene. Addition of aluminum chloride to a solution of a 4-ene-3,6-dione followed by treatment with LiAIH4 gives the 4-ene-6-one. Steroid 4,6-dien-3-ones yield mixtures of dienes. When the ketone and double bond are in different rings the results become even more complex dienes as well as mono-enes are obtained. 

Consequently, due to preferred cis-cis orientation a dimeric structure is observed for the indium complex and an unprecedented cis-trans arrangement in the thallium structure leads to a polymeric aggregate. Further N-NMR spectroscopic studies show that the aluminum and gallium complexes are stable contact ion pairs even in solution whereas the indium and thallium compounds are solvent-separated ion pairs in THE solution. 

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