Magnesium complexes naturally occurring

Fig. 2.136. Molecular structures of (a) naturally occurring magnesium chlorin, bacteriochlorophylls-d (Bchls-d), (b) their synthetic analogues, methyl bacteriopheophorbides-d (MBPhes-d, and (c) 3 -epimeric zinc complexes (Zn-MBPhes-d). Reprinted with permission from S. Sasaki et al. [307],...

Magnesium forms an array of silicates having varying structures. Such a wide variety of silicates include metasilicate, orthosilicate, pyrosilicate, polysilicates, and a number of complex silicates, such as asbestos and talc in combination with other metal ions. Many such silicates occur in nature either as complex silicates or as discrete magnesium silicate. Some important magnesium silicates are listed below ... 

Of some interest is the ability of 3-acyltetramic acid to form stable complexes with ions of transition metals, e.g. Cu2+, La3+, Sm3+, Eu +, Gd3+, and boron complexes [1]. Indeed, examples are available in which the tetramic acid occurs naturally as magnesium or calcium salts. Methods of isolation or purification involving acidic solvents generate conditions that... 

However, it is noteworthy that oxygen atom transfer to the magnesium alkyl derivative does not occur rapidly at room temperature. This is presumably one of the factors that is responsible for the observation that the reactions of [Tp ]MgR with O2 are selective in the formation of alkylperoxo complexes, rather than the alkoxo derivatives. It is likely that this is a consequence of the sterically encumbered nature of the magnesium centers in these complexes. 

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