Metal-ion coordination chemistry

The macrocyclic revolution in metal ion coordination chemistry [115] soon had repercussions on the design of fluorescent sensors for alkali cations. Before the advent of PET sensors, the first examinations of crown ether receptors with adjacent n-eleetron systems such as naphtho- and benzo crown ethers (50) [116] and (51) [117, 118] showed small but significant alkali cation induced fluore-... 

The great impact in metal-ion coordination chemistry caused by the discovery of the macrocyclic polyethers31 has led to new designs of chemosensors for the alkali cations. Application of a supramolecular receptor to fluorescence sensing was first... 

Unlike ATXl, where the chemistry of copper transfer is well understood, the mechanism of copper transfer from CCS to SODl remains unclear. For example, a dramatic change in metal ion coordination chemistry must accompany the copper transfer process in this case. Copper is bound to CCS in the reduced Cu(I) form via sulfhydral ligands, while in SODl, copper is oxidized to the cupric Cu(II) state and is coordinated in an all-nitrogen environment to four histidines. The driving force for this large change in coordination chemistry is still poorly understood, but may involve an external oxidant, such as the superoxide substrate itself... 

See Schmidbaur. H. CIas,scn. H. G. Helbig, J. /t/igew. Chvm. Ini. Ed. Engl. 1990, 29. 1090-1103 for biologically important comple.xes of alkaline earth and alkali metal ions. Coordination chemistry of alkali metal and alkaline earth ions is also discus.sed in Poonia, N. S. Bajaj, A. V. Client. Rev. 1979. 79. 389-445. 

Comprehensive reviews of divalent metal ion coordination chemistry and kinetic behavior can be found in standard references such as Cotton and Wilkinson (7) and the works of Eigen and Wilkens (2—5). Therefore, discussion of zinc coordination complexes here is restricted to consideration of those aspects of zinc chemistry which relate to the catalytic properties of Zn-metalloenz3maes. 

Of all the diheterocins, those with the two heteroatoms in a 1,5-relationship have received perhaps the greatest attention, although this attention has been focused primarily on the diaza and dithia compounds. Interest in the 1,5-diheterocins appears more broadly bas than that in the other positional isomers, with both demonstrated and potential pharmacological activity, versatile metal ion coordination chemistry, and unusual chemical properties, including a number of transannularly bonded systems, representing a few of the diverse array of reported studies. 

Given the comparatively large amount of attention paid to the 1,5-diazocines, exhaustive coverage of their structural and chemical features is beyond the scope of this chapter. CHEC-I reviewed the earlier literature, and more recent comprehensive reviews of the 1,5-diazocines (Section 5.19.7.5) <89AHC(i6)i> and the benzodiazocines <87H(26)2477>, as well as the metal ion coordination chemistry of the diazocines <92CCR133>, have appeared. This section, then, provides comprehensive coverage of the literature from 1987 to 1995, with occasional reference to earlier work as appropriate. 

The preparation and reaction chemistry of the 1,5-dithiocanes was surveyed in CHEC-I. The metal ion coordination chemistry of 1,5-dithiocane (5) and its derivatives has been reviewed <92CCR133>, as has the chemistry of transannularly-bonded dicationic derivatives <80ACR200,89JST(55)26i, 92RHA263). 

The use of metals as part of anion receptors is well estabhshed and the versatility of metal ion coordination chemistry has led to their varied use in receptor design, and we covered some examples in Section 1.7. In general, there are five major classes of metallic receptors ... 

N-heterocyclic compounds containing six-membered rings (pyridine and analogues) behave as excellent -acceptors and in turn they provide a rather soft site for metal ion coordination. The 7r-excessive five-membered pyrazole is a poorer 7r-acceptor and a better 7r-donor and it acts as relatively hard donor site. Inclusion of six- and five-membered N-heterocycles like pyridine and pyrazole in one ligand system leads to very attractive coordination chemistry with variations of the electronic properties.555 The insertion of a spacer (e.g., methylene groups) between two heterocycles, which breaks any electronic communication, makes the coordination properties even more manifold. 

Bob s research interests and knowledge across chemistry were great. Throughout his career he retained an interest in biomimetic chemistry, specifically the study of metal ion-promoted reactions and reactions of molecules activated by metal ion coordination. His early interests in carbohydrate chemistry inspired him to study metal ion catalysis of both peptide formation and hydrolysis as well as studies in inorganic reaction mechanisms. He was particularly interested in the mechanisms of base-catalyzed hydrolysis within metal complexes and the development of the so-called dissociative conjugate-base (DCB) mechanism for base-catalyzed substitution reactions at inert d6 metal ions such as Co(III). 

Hydroxyquinoline, whose chemistry has been reviewed (56CRV271), has found wide application as an analytical reagent, and is known as oxine . It forms insoluble complexes with a great many metal ions, coordinating at O and N, and can be used for the estimation of Mg, Zn, Al, Cu, Bi, Fe, Mn, Ni and others. 

The coordination chemistry of oxalate (ox, C2042-) compounds provides a series of very interesting compounds from the stereochemical and magnetic points of view [197]. Most frequently the compounds form honeycomb layers in the presence of transition metal ions, in which the stereochemistry of the metal ion coordination sphere alternates between A and A. However, a three-dimensional homochiral structure is also possible. On the other hand, the negative charge of the oxalates necessitates the incorporation of cations between them, which provides the opportunity to introduce chirality and additional functionality in materials. The compound formed between homochiral manganese II oxalate and iron II tris bipyridinc (bpy) with formula [Mn oxls]2 " [Fcn(bpy)3]2+ crystallises in the space group fJ4 32. 

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