Magnesium carboxylate ligands

The earliest example of a coordination tetrahedron was reported by Saalfrank and coworkers [144], Their study showed the formation of the tetranuclear magnesium(II) complex 30 bridged by six tetra-carboxylate ligands 29, representing the first reported coordination tetrahedron exhibiting M4L6 stoichiometry (Fig. 21). This serendipitous discovery was followed by the formation of other, pre-designed tetrahedral architectures [19,122,145]. 

Calcium-selective electrodes have long been in use for the estimation of calcium concentrations - early applications included their use in complexometric titrations, especially of calcium in the presence of magnesium (42). Subsequently they have found use in a variety of systems, particularly for determining stability constants. Examples include determinations for ligands such as chloride, nitrate, acetate, and malonate (mal) (43), several diazacrown ethers (44,45), and methyl aldofuranosides (46). Other applications have included the estimation of Ca2+ levels in blood plasma (47) and in human hair (where the results compared satisfactorily with those from neutron activation analysis) (48). Ion-selective electrodes based on carboxylic polyether ionophores are mentioned in Section IV.B below. Though calcium-selective electrodes are convenient they are not particularly sensitive, and have slow response times. 

At present, only two organomagnesium derivatives of terphenyl ligands have been well characterized. However, the first terphenyl magnesium compound was reported more than 60 years ago with the generation of BrMgTriph in solution and its subsequent reactions to give the carboxylic acid, the acetyl derivative, and triphenylbenzophenone.28... 

Yun et al. have reported a carboxylate- and a phosphodiester-bridged dinuclear magnesium(II) complex with dicarboxylate ligand 52 (56). The reaction of 52 with 2 equivalents of Mg(N03)2 in MeOH gave a carboxylate-bridged complex 53 (see Scheme 12). The Mg-Mg distance... 

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