Aluminium coordination

This species undergoes an intramolecular 1,3-hydride shift that results in the production of the aluminium-coordinated ester. 

A1 NMR spectroscopy can also be used for the determination of aluminium coordination environments in solid samples. Examples of spectra from the clay minerals kaolinite and saponite, which show respectively octahedral and tetrahedral coordination of oxygen atoms around their aluminium atoms, are shown in Fig. 3.7. 

Mechanism The aluminium alkoxide complex A (of starting alcohol and aluminium alkox-ide) reacts with ketone (hydrogen acceptor) to form aluminium coordination complex B. Transfer of hydrogen takes place via a cyclic transition state to give the oxidized product ketone of the starting alcohol and aluminium alkoxide C, which releases 2-propanol (Scheme 7.12). 

Solid-state Al NMR studies have been carried out of the aluminium coordination environments in TaAl tellurite glasses containing from 60 to 95 cation-% Xe02. These data show the presence of 4-, 5- and 6-coordinate aluminium in all glasses. ... 

Now the two parts, 184 and 199, must be linked in a controlled aldol reaction. The lithium enolate 200 reacts with the aldehyde in 199 in the presence of excess Lewis acid Me2AICI to give one diastereoisomer of 201 as the only product. Presumably the aluminium coordinates the tertiary amide and aldehyde oxygen atoms to hold the aldehyde in one Felkin conformation while it is attacked by the lithium enolate from one face only as sketched in 202. 

Wilson, M.A., Barron, RF, and Campbell, A.S. Detection of aluminium coordination in soils and clay fractions nsing A1 magic angle spinning n.m.r. 1984 35 201-207. 

Omegna, A., Van Bekhoven, J.A., and Prins, R. Flexible aluminium coordination in alumino silicates. Structure of zeolite H-USY and amorphous silica-alumina. J. Phys. Chem. B 2003, 107, 8854-8860. 

Exley, C., Schneider, C. Doucet, F.J. (2002) The reaction of aluminium with silicic acid in acidic solution An important mechanism in controlling the biological availability of aluminium Coordination Chemistry Reviews, 228,127-135. 

The main advantage of solid-state NMR spectroscopy in studies of cement-based materials is its ability to detect and quantify amorphous and crystalline phases in an equal manner. This property and the fact that the detected NMR parameters are most sensitive to the local structure, roughly the nearest one to three coordination spheres, makes it a valuable and important supplement to XRD techniques that probe long-range order and crystalline phases. Moreover, the nuclear-spin selectivity often implies that unambiguous structural or quantitative information can be achieved for a subsystem of a complex multicomponent material. For example, Al MAS NMR provides direct information about the aluminium coordination state and, for Portland cement systems, it allows identification of aluminium in tricalcium aluminate, as guest ions in the alite and belite phases, in the AFm and AFt hydration products and as a part of the C-S-H structure, despite a low bulk AI2O3 content of 2-5 wt.% for such systems. 

Muller, D., W. Gessner, H. J. Behrens and G. Scheler. 1981. Determination of the aluminium coordination in aluminium-oxygen compounds by solid-state high-resolution Al NMR. Chem. Phys. Lett. 79, 59-62. 

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