Complex formation transition metal cation with

Figure 29 Assembling a dumbbell chelate (B) and an open chelate (A) around a transition metal cation with a kinetically labile coordination sphere will provide a mixture of homoleptic ((D) and (E)) and heteroleptic (C) complexes. Only the latter will be productive for the formation of a [2]-rotaxane.

The enhanced selectivity of the complexed transition metal cation compared to the uncomplexed aqueous form can be expressed as a gain in the stability constant of the adsorbed complex with respect to its stability constant in the solution phase (80). The complex formation reaction and corresponding stability constants of a transition metal cation M with an uncharged ligand L in both the surface (indicated by bars) and solution phase are defined as... 

Separation is based on the reversible chelate-complex formation between the chiral selector covalently bonded to the chromatographic support, and the chiral solute with transition metal cations. Chelation properties of both the chiral selector and the chiral solute are required. Compounds therefore need to have two polar functional groups in a favorable arrangement to each other, like a )3-amino acids, amino alcohols and a-hydroxy acids, which can form rings membered with central chelating metal ions, like Cu(II), Zn(II), Cyclic... 

The formation of the bimetallic complexes 118-123 involves combination of di-cationic transition metal fragments with the dianion of compound 14. A further possibility exists, scarcely studied for 12-vertex 0/050-2,l-ReCBjo species but more extensively exploited in the analogous 11-vertex c/o5o-l,2-MCBg system (M = Mn, Re) discussed in Section IV. Treatment of the dianion of 14 with two... 

As described above, the catalytic activity of metal ion-exchanged zeolites for aniline formation has a good correlation with electronegativity and with the formation constant of ammine complexes of metal cations. The order of the activity agrees with the Irving-Williams order. These facts give irrefutable evidence that the transition metal cations are the active centers of the reaction. 

Lipid hydroperoxides arise in membranes and in oxidised LDL as a direct consequence of the intervention by a-T in terminating chain reactions, as well as from the chain reactions themselves. The possibility exists that catalysis by divalent transition metal cation complexes may cause the re-formation of lipid-peroxyl radicals or of other radical species such as the alkoxyl radical. The rate of reaction of Fe3+ with lipid hydroperoxides is much slower than the rate of... 

Apart from some Weakley-type complexes (Table 22), there has been little systematic investigation of lanthanide-molybdate complexes. Multinuclear NMR studies of solutions of the well-established dodecamolybdates [MIVMo12042]8- (M = Ce, U), with a range of di- and trivalent transition-metal and lanthanide cations, show the formation of complexes incorporating two metal cations. In most cases these complexes are labile on the NMR timescale.368-370... 

The effect of NH3 adsorption on catalytic activity and selectivity of cation-exchanged Y zeolite and natural clinoptilolite (deposit of Georgia) in ethanol transformation was investigated. The ODH of alcohol is accompanied by dehydration to ethylene and diethylether and deep oxidation to CO2 NH3 blocks the acidic active centers of dehydration of Y zeolites and promotes the oxidative activity of samples with transition metal cations. The influence of the ion nature for the catalytic transformation of ethanol was shown by a considerable increase of carbon dioxide formation after NH3 adsorption. The cation associated has been destroyed under NH3 influence, and NH3 formed with cations coordinated-unsaturated complexes. 

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