Complexes magnesium

All organisms seem to have an absolute need for magnesium. In plants, the magnesium complex chlorophyll is the prime agent in photosynthesis. In animals, magnesium functions as an enzyme activator the enzyme which catalyses the ATP hydrolysis mentioned above is an important example. 

Porphyrin, octaethyl-, magnesium complex cyclic voltammetry, 4, 399 <73JA5140)... 

In the above reactions the magnesium complex is specifically active catalyst. Neither fl,fl-DBF0X/Ph Zn(Cl04)2 3H20 (10) nor fl,fl-DBF0X/Ph Ni(CI04)2 3H2O (10) shows any catalytic activity. 

These results imply that at the specified pH the magnesium complex is appreciably dissociated, whereas the lead complex is stable, and clearly titration of an Mg( II) solution with EDTA at this pH will be unsatisfactory, but titration of the lead solution under the same conditions will be quite feasible. In practice, for a metal ion to be titrated with EDTA at a stipulated pH the value of log K H should be greater than 8 when a metallochromic indicator is used. 

C. Replacement or substitution titration. Substitution titrations may be used for metal ions that do not react (or react unsatisfactorily) with a metal indicator, or for metal ions which form EDTA complexes that are more stable than those of other metals such as magnesium and calcium. The metal cation M + to be determined may be treated with the magnesium complex of EDTA, when the following reaction occurs ... 

Prepare the magnesium complex of EDTA, Na2MgY, by mixing equal volumes of 0.2M solutions of EDTA and of magnesium sulphate. Neutralise... 

Two independent routes to magnesium amidinates containing very bulky terphenyl substituents have been developed, yielding both mono- and bis(amidinate) magnesium complexes. As shown in Scheme 17, the free amidine reacted cleanly with 0.5 equivalents of dibutylmagnesium in toluene to form the bis (amidinate) in moderate yield. The highly soluble compounds was recrystallized from hexanes as clear, colorless crystalline blocks. ... 

By using an alternate synthetic route, a mono(amidinate) magnesium complex was obtained. In this case, the Giignard reagent formed by treatment of the terphenyliodide with Mg was allowed to react directly with 1 equivalent of 1,3-diisopropylcarbodiimide, yielding the amidinate (Scheme 18). ... 

N,N -Chelation is also exhibited by the dianionic P(III)/P(V) ligands (25) in the MejSn complex (31) [39] and in the magnesium complex (32) [40], which is prepared by oxidation of [Mg(thf)2[ BuNP(p-N Bu)2PN Bu] by elemental tellurium [40]. One of the endocychc N Bu groups in (32) is also weakly coordinated to magnesium, thus providing an intramolecular base-stabihzation similar to that observed for complexes of type (8). 

Figure 10-4. Adenosine triphosphate (ATP) shown as the magnesium complex. ADP forms a similar complex with Mg A...

Figure 10 The structure of the lithium-magnesium complex [Li(tmeda)(/r-Br)2Mg C(SiMe3)2(SiMe2Ph) (THF)] 23. 

Figure 53 The structure of the ethynyl-bridged aluminum-magnesium complex [Me2AI(/i-EtN)2Mg(/j-Cs=CPh)]2 106.

If the analyte metal ion forms a stable EDTA complex rapidly, and an end point can be readily detected, a direct titration procedure may be employed. More than thirty metal ions may be so determined. Where the analyte is partially precipitated under the reaction conditions thereby leading to a slow reaction, or where a suitable indicator cannot be found, back titration procedures are used. A measured excess of EDTA is added and the unreacted EDTA titrated with a standard magnesium or calcium solution. Provided the analyte complex is stronger than the Ca-EDTA or Mg-EDTA complex a satisfactory end point may be obtained with eriochrome black T as indicator. An alternative procedure, where end points are difficult to observe, is to use a displacement reaction. In this case, a measured excess of EDTA is added as its zinc or magnesium complex. Provided the analyte complex is the stronger, the analyte will displace the zinc or magnesium. 

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