Crystal magnesium compounds

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. 

Table 2 Relevant Bond Lengths (A) and Bond Angles (°) from the Crystal Structures of Diorgano-magnesium Compounds...

Unlike Grignard reagents, crystal structures of dicoordinated organomagnesium compounds are known. These are formed when sterically hindered ligands cause excessive crowding in the environment around the Mg atom and prevent the coordination of any solvent molecules. The X-ray structure of bis[tris(trimethylsilyl)methyl]magnesium [Compound 19] indicates that the compound is linear (C—Mg—C=180°) and is centrosymmetric around the Mg atom [21]. 

The crystal structures of another group of magnesium compounds without Mg—C bonds are also relevant, and some of the bond lengths and angles are given in Table 5. 

The crystal structures of indenyllithium-TMEDA, indenylsodium-TMEDA ° and bis(indenyl)mag-nesium ° are also known. These three structures are all different. The lithium compound is monomeric with Ti -coordination the sodium compound is infinitely aggregated with both ii - and tt -bonding and the magnesium compound appears to include all three types of interactions, i.e. ii -, and -bonding, of magnesium to the indenyl anion. 

Bickelhaupt and coworicers have determined the crystal structures of a series of crown ether solvated magnesium compounds. A sequence of these compounds is illustrated as the internally coordinated 13-crown-4-xylylmagnesium chloride (134) and bromide (135), as well as the organometallic, rotaxane (136). Note the similarity between these structures and the corresponding aliphatic dialkylmagnesium rotaxane (83). 

Some magnesium compounds are important over-the-counter medicines. For example, milk of magnesia is a suspension of magnesium hydroxide (Mg[OH]2) in water. This creamy liquid suspension is used as an antacid to neutralize excess acid in the stomach. Another magnesium compound remedy is Epsom salts, which are used to treat certain skin rashes. Discovered in Epsom, England, in 1618, these are crystals of magnesium sulfate evaporated from water. 

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