Aluminum-27 NMR Parameters

By far the major effort in the field has gone into studies of chemical shift effects, and these will be studied first. Many of the older data have now been superceded, and where this is the case will not be referred to, an adequate cover being available in the earlier reviews. Quite an impressive list of coupling constants has now been accumulated and these follow the shift/linewidth data with the few relaxation data last. 

Broadly speaking, the chemical shift range observed can be separated into three regions (a) alkylaluminum compounds 150 ppm and more to low field of the reference, Al(H20)g (b) tetrahedrally coordinated aluminum with d between 140 and 40 ppm (c) octahedrally coordinated aluminum between 40 and —46 ppm. There are some exceptions to this generalization, notably All, which resonates at —26.7 ppm, but the shift is often a good indicator of coordination number. There are other recently noted exceptions and five-coordinated aluminum is said to resonate between the octahedral and tetrahedral regions we will return to this point after we have considered the data. 

The linewidths which are presented are a function of temperature, of concen- 

The fact that the linewidth of A1(H20) + varies with solution conditions has already been mentioned. It becomes broader if a concentrated solution is heated, but is narrowed if acid is added. It is also broadened in the presence of the dimeric cation, especially if the solution is heated when it may not be detectable in older equipment. It has now been discovered that in very dilute, pure salt solutions the 

Other Aqueous Systems. Several reports have appeared where bidentate ligands have been attached to aluminum either as tris complexes or as partially aquated complexes. Of particular interest is the use of Al to study the macrocyclic 

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