Aluminium, structure determination

Since the first structure determination by Wadsley [56] in 1952 there has been confusion about the correct cell dimensions and symmetry of natural as well of synthetic lithiophorite. Wadsley determined a monoclinic cell (for details see Table 3) with a disordered distribution of the lithium and aluminium atoms at their respective sites. Giovanoli et al. [75] found, in a sample of synthetic lithiophorite, that the unique monoclinic b-axis of Wadsley s cell setting has to tripled for correct indexing of the electron diffraction patterns. Additionally, they concluded that the lithium and aluminum atoms occupy different sites and show an ordered arrangement within the layers. Thus, the resulting formula given by Giovanelli et al. 

In addition, Pauling and Sherman (222) had proposed a ring structure for the anion of aluminium tetrametaphosphate on the basis of a crystal structure determination. The triphosphate NaBP3Oi0 must, then, have the chain structure already proposed by Schwarz (263), for Rudy and Schloesser (250) showed that the acid corresponding to the triphosphate has three strongly and two weakly acidic OH groups with the weakly acidic groups... 

No well-characterized indium imido derivative was known in 1980. In the past decade several examples have been synthesized and their structures determined. At present, however, their structural diversity does not match those of aluminium or gallium. The highest degree of aggregation currently known is four. 

Each Ca " ion in C4AF has 7 oxygen neighbours at 0.23-0.26 nm (C3). The aluminium and iron atoms are both distributed between octahedral and tetrahedral sites, the fraction of the aluminium entering tetrahedral sites under equilibrium conditions decreasing with temperature. For the three preparations with. y = 0.285, 0.36 and 0.5 on which X-ray structure determinations were made, 75-76% of the total content of aluminium was found to be in tetrahedral sites. These preparations were shown to have been in equilibrium at about 750°C (C3) for a C4AF preparation quenched from... 

The -Alumina-related Structures.—Originally the compound )3-alumina was taken to be a binary aluminium oxide, but early Y-ray structure determinations and associated chemical analysis showed that the formula was approximately NaAlnOi7. Since then a number of isostructural compounds have been characterized in which sodium is replaced by other monovalent ions, particularly silver, and aluminium by other trivalent ions, notably gallium and iron. In addition, a number of other phases have been prepared which are structurally closely related to )8-alumina. Four principal structures are known, which are labelled / ", and P"". These can also be prepared with other monovalent cations replacing sodium, and some seem only to be formed when a few per cent of divalent cations, particularly magnesium, are present, so that they are, in fact, quaternary phases. The structure and stoicheiometry of these compounds has been summarized recently and we will only consider here those aspects relevant to the present topic. 

To demonstrate the usefulness of the MD/DF approach, we now discuss applications to structure determination in clusters of elements of groups 13, IS, and 16. Clusters of the last two are typically covalently bonded systems. The bulk systems are generally semiconductors or insulators, and there is a substantial energy gap between the highest occupied and lowest unoccupied molecular orbitals. The first, typified by aluminium, show aspects of metallic behaviour. One of the advantages of the DF method is that it can be applied with comparable ease to elements of all atomic numters. 

X-ray structure determinations of the sodium salt of tropolonc [259] and of tris(tropolonato)aluminium [260] also show long C(l) - C(2) bonds. Rather than bond alternation in the ring, there is a sequential decrease in C-C bond distances proceeding from C(l), 0(2 to the carbon atom furthest from the oxygen atoms. 

Cedergren-Zeppezauer E, Samama J-P, Eklund H (1982) Crystal structure determinations of coenzyme analogue and substrate complexes of liver alcohol dehydrogenase Binding of 1,4,5,6-tetrahydronicotin-amide adenine dinucleotide and trans-4-(N,N-dimethylamino)cinnam-aldehyde to the enzyme. Biochemistry 21 4895-4908 Cherest M, Felkin H, Prudent N (1968) Tortional strain involving partial bonds. The stereochemistry of the lithium aluminium hydride reduction of some simple open-chain ketones. Tetrahedron Lett 2199-2204... 

M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

We alluded earlier to the variety of structural modifications which may he observed in sheet silicates. Clearly it is a matter of considerable in jortance to he able to determine if, for example, the aluminium content within a clay arises p a ely from octahedral substitution (as in montmorillonite) or whether there is some tetrahedral component (as in heidellite). a1 MASNMR readily provides the necessary answers. Figvire 1 illustrates the a1 spectrum for a synthetic heidellite material with Na as charge balancing cation. Aluminium in two distinct chemical environments is observed, with chemical shifts corresponding to octahedrally and tetrahedrally co-ordinated aluminium. 

Yoshino reports a novel and general method for the C-3 acylation of indoles with acyl chlorides in the presence of dialkylaluminium chloride which obviates the need for prior N-protection . Interestingly, as described in this preliminary communication, the unprotected indoles 147 are first treated with the Lewis acids prior to addition of the acid chlorides, yielding the desired 3-acyl derivatives 148. In reactions more typical of indoles under acidic conditions, Nakatsuka determined the structures of the dimers and trimers of 1-trimethylacetylindole produced in the presence of aluminium chloride . 

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