Crystal structures magnesium

Even acetophenone reacts with the magnesium compound 17 (R1 = R2 = H) to yield the w-diastereomer 18 with 90 % de 22 24. The structure of the metal-organic precursor and, as well, of the major product was determined by an X-ray crystal structure analysis23. 

Marble. The word marble is used as the common name for two types of monomineral rocks one derived from limestone and therefore composed of calcium carbonate, the other derived from dolomite and composed of calcium magnesium carbonate. Extremely high pressures and heat during past geological times modified the structure of both limestone and dolomite, compacting them into a characteristic crystal structure. Most marble is white however, minor and trace amounts of metallic impurities cause the formation of stains in a variety of colors, hues, and patterns, or of colored marble. 

The bones and teeth of humans and other vertebrate animals, for example, consist mainly of a composite material made up of an organic substance, collagen, and a biomineral, calcium carbonate phosphate (see Textboxes 32 and 61). The latter, which makes up about two-thirds of the total dry weight of bone, is composed of calcium phosphate containing between 4-6% calcite (composed of calcium carbonate) as well as small amounts of sodium, magnesium, fluorine, and other trace elements. The formula Ca HPChXPChMCChXOH) approximately represents its composition its crystal structure is akin to that... 

Talc is a hydrated magnesium silicate, Mg6(Si802o)(OH)4. It is a layerd compound like mica. One layer of its crystal structure is shown schematically in Figure 11.3. Such layers are stacked up like playing cards in real crystals. Notice that the top and bottom of the layer consist of slicate tetrahedra with oxygen... 

Figure 113 Schematic crystal structure of one layer of talc. Such layers are stacked to make the complete structure. The large and medium open circles represent oxygen atoms.The cross-hatched large circles represent hydroxyls (OH).The small open circles represent magnesium atoms (Mg) and the cross-hatched small circles represent silicon (Si) atoms. Figure is reproduced from Bragg, Claringbull and Taylor (1965).

Similarly, dilithiation of 2-(4-bromophenoxy(ethanol in the presence of magnesium 2-ethoxyethoxide followed by reaction with 0.5 equiv. of HgCl2 afforded the corresponding diarylmercury compound 4-(H0(CH2)20)-C6H4)2Hg 26 whose crystal structure has been determined (Equation (12)).47 In addition to these alcohol and ether derivatives, thio- and phosphinoaryl mercury compounds have also been prepared. Thus, the dilithium salt... 

Magnesium chloride has a crystal structure very similar to violet titanium trichloride. This dictates the possibility of an epitaxial coordination of TiCU units (or TiCl3 units, after reduction) on the lateral coordinatively unsatured faces of MgCl2 crystals, giving rise to relieves crystallographically coherent with the matrix.150... 

Anhydrous magnesium sulfate. In my opinion, anh. MgS04 is about the best all-around drying agent. It has a drawback, though. Since it is a fine powder, lots of your product can become trapped on the surface. This is not the same as water of crystallization. The product is only on the surface, not inside the crystal structure, and you may wash your product off. 

Figure 3 Crystal structure of a magnesium salt of mixed half-sandwich chloroyttraVchloromagnesacarborane complex. Reproduced by permission of the American Chemical Society from Organometallics 1998, 17, 3196.

Interpretation of the electron density maps showed that the large subunit could not be modelled beyond His536 (Fig. 6.10), that is fifteen amino acids short of the 551 residues predicted by the nucleotide sequence (Table 6.2). At about the same time, the cleavage of this fifteen-residue stretch, which is performed by a specific protease, was reported to be an obligatory step for the maturation of the enzyme (Menon et al. 1993). It is also of interest to note that in all [NiFe] hydrogenase crystal structures this buried C-terminal histidine is ligated to a metal atom which is either a magnesium or an iron (see above). 

The resolution of the PDB 1X8W crystal structure does not allow identification of magnesium ions. However, heavy atom [europium (Eu) and iridium. 

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