The stability of complexes

As the results make immediately clear (Tables 7—10), it is among ligands of the macrobicyclic type G (27—44), which give complexes of the [2]-cryptate type, that by far the highest stability constants may be found for any cation. In particular, these optimum Ks values are several decades higher than those of the most stable complexes formed by natural ligands, 

Design of Organic Complexing Agents. Strategies towards Properties 

The chelate effect is a celebrated feature of the chemistry of transition metal complexes. Ligands containing an increasing number of rings show several such ring order effects. 

A chelate effect is expected to be operative in ligand 2 as compared with dimethylether, for example unfortunately, the stability constants for the latter compound are not known. 

A tripod effect is probably present in ligand 4 according to the results of Table 7 this factor leads to about the same stabilities as linear chelates. 

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The ligand pATa values and transition metal chelate stability constants of arylisoxazoles were detected photometrically and the stability of the complexes studied (79JlCi25i). 

Class-b acceptors on the other hand are less electropositive, have relatively full d orbitals, and form their most stable complexes with ligands which, in addition to possessing lone-pairs of electrons, have empty n orbitals available to accommodate some charge from the d orbitals of the metal. The order of stability will now be the reverse of that for class-a acceptors, the increasing accessibility of empty d orbitals in the heavier halide ions for instance, favouring an increase in stability of the complexes in the sequence... 

Upon formulating these relationships, phenols with branched alkyl substituents were not included in the data of a-cyclodextrin systems, though they were included in (3-cyclodextrin systems. In all the above equations, the n term was statistically significant at the 99.5 % level of confidence, indicating that the hydrophobic interaction plays a decisive role in the complexation of cyclodextrin with phenols. The Ibrnch term was statistically significant at the 99.5% level of confidence for (3-cyclo-dextrin complexes with m- and p-substituted phenols. The stability of the complexes increases with an increasing number of branches in substituents. This was ascribed to the attractive van der Waals interaction due to the close fitness of the branched substituents to the (3-cyclodextrin cavity. The steric effect of substituents was also observed for a-cyclodextrin complexes with p-substituted phenols (Eq. 22). In this case, the B parameter was used in place of Ibmch, since no phenol with a branched... 

Hexaammonium macrocycles [32]aneN6 and [38]aneN6 were designed as selective ditopic receptor molecules for dicarboxylates -02C—R—C02- such as succinate, glutarate, or adipate 51). Highest stability of the complex corresponds to the best fit between the substrate R length and the site separation of the receptor II. 

Another features of the ligand lipophilicity and the- stability of the complex on the rates are shown in Fig. 6 Rate saturation corresponds to the formation of a 1 1 or 2 1 ligand-metal ion complex. Non-micellar reactions of curves b and c indicate that the N-butyl ligand 38b forms a more active complex than N-methyl ligand 38a does. It may be interesting to note that in the micellar reaction of 38b, a flat... 

The anions MeF6 and X approach each other closely to form the heptacoordinated complex MeF6X(n+1)", or separate from one another, according to the polarization potential of the outer-sphere cation (alkali metal cation -M+). This process is unique in that the mode frequencies of the complexes remain practically unchanged despite varying conditions. This particular stability of the complexes is due to the high charge density of Ta5+ and Nbs+. 

The authors found that the yield of 30-mer (a product with 5—6 linkages) was not much smaller than that of 10-mer or 12-mer. These facts indicate that the stability of the complex between the oligonucleotides and the complementary template is the most important factor in determining the extent of the condensation. The strong influences of template polymer (Poly C) are demonstrated in Fig. 9, in which the elution profile is shown of the polymerization products of (2 MeIp)6 in the presence of Poly C (B) and in their absence (A). 

The low stability of the complex 3.6 is consistent with the hard and soft acids and bases principle of Pearson (1963, 1968 Parr and Pearson, 1983 theoretical aspects Pearson, 1989 Chatteraj et al., 1991 monograph Ho, 1977). According to that principle hard acids will tend to complex with hard bases and soft acids with soft bases. Water is a hard base, whereas the nitrosyl ion is classified by Pearson as a borderline acid with a tendency to be soft. 

The overall stability of the complexes listed in Table II tends to parallel, but exceed, that of their alkyl counterparts. Their chemical reactions may be classified as shown in the headings to Sections II,C,l-5, respectively, of which the Si—M cleavages (Section II,C,3) have been the most studied. 

This involves deposition of the catalyst on the accessible surface of the support. The complex is held on the surface by rather weak interactions, such as van der Waals forces, hydrogen bonding, or a donating bond. The stability of the complex on the surface is determined by its solubility in the reaction solvent and/or the complexation of reagents and products. 

The stability of the complexes based on DNA condensation is a legitimate issue for nanoassemblies based on DNA. Under in vivo conditions, DNA as a constituent of a gene... 

It has been found that DTBP cross-linking substantially increased the salt stability of the complexes. The salt stabilization is reversed upon the addition of DTT, which cleaves the bifunctional reagent, indicating that it is not due to the conversion of the amines to amidines and is dependent upon the cross-linking. Similar results were achieved with other polycations, including poly(allylamine), and histone HI. 

Setting times and hydrolytic stability of these cements are given in Table 8.3. In some cases the speed of reaction was very high, and practical cements could not be formed from ZnO or CaO even when these oxides were deactivated by heating. All the faster-setting cements exhibited good hydrolytic stability. The stability of the complexes between divalent cations and PVPA was found by a titrametric procedure to follow the order Mg Ca < Cu Zn (Ellis Wilson, 1991). This result was... 

The composition of the electrolyte is quite important in controlling the electrolytic deposition of the pertinent metal, the chemical interaction of the deposit with the electrolyte, and the electrical conductivity of the electrolyte. In the case of molten salts, the solvent cations and the solvent anions influence the electrodeposition process through the formation of complexes. The stability of these complexes determines the extent of the reversibility of the overall electroreduction process and, hence, the type of the deposit formed. By selecting a suitable mixture of solvent cations to produce a chemically stable solution with strong solute cation-anion interactions, it is possible to optimize the stability of the complexes so as to obtain the best deposition kinetics. In the case of refractory and reactive metals, the presence of a reasonably stable complex is necessary in order to yield a coherent deposition rather than a dendritic type of deposition. 

The strong backbonding from the chelated diphosphine Pd(0) metal center to the electron-poor exocylic C=C bond of the QM moieties results in remarkable stability of the complex, with the QM ligand remaining unaffected in water or alcohol, even upon heating. 

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