Stability constant acetylacetonate

However, even this simplified formula does not justify the use of the ratio of stability constants of the extracted complexes as the only measure of selectivity of extractive separations. Such a widely used approach is obviously based on an implicit assumption that the partition constants of neutral complexes ML of similar metal ions are similar, so that their ratio should be close to unity. This is, however, an oversimplification because we have shown that the ifoM values significantly differ even in a series of coordi-natively saturated complexes of similar metals [92,93]. Still stronger differences in the values have been observed in the series of lanthanide acetylacetonates, due to different inner-sphere hydration of the complexes (shown earlier), but in this case, self-adduct formation acts in the opposite direction [100,101] and partly compensates the effect of the differences in. Tdm on S T(see also Fig. 4.15). Such compensation should also be observed in extraction systems containing coordinatively unsaturated complexes and a neutral lipophilic coextractant (synergist). 

The structure of bis(salicylaldoxime)beryllium has been proposed as being trans octahedral by comparison of the space group and unit cell volume with those of related transition metal complexes it is presumably a dihydrate if it is indeed octahedral in geometry.297 Stability constants have been reported for a range of beryllium /3-ketoamines derived from both salicylaldehyde and acetylacetone precursors. They show strong complexes which are stable to hydrolysis under the conditions used.298,299... 

Table 33. Stability constants of the acetylacetonate complexes of the rare earths [429] (p = 0.1 at 30° C)...

An = Th, U, Np, and Pu. In complexing with metal ions, the / -diketones form planar six-member chelate rings with elimination of the enol proton. The simpler / -diketones, such as acetylacetone (HAA), are fairly water soluble, but form complexes that may be soluble in organic solvents. This is especially true for the An ions which form strong complexes with HAA and can be effectively sequestered to the organic phase, making HAA a potentially useful extractant (See Table 27). The four stability constants in Table 27 for tetravalent actinides imply that four HAA ligands coordinate with each metal ion in the formation of the extracted neutral ML4 complexes. ... 

Table 27 Stability constants for acetylacetonate complexes and distribution constants (from benzene or...

Table 21.12 Stability of acetylacetonate complexes in aqueous solution and the distrU bution constants of the neutral complexes M AA)x between benzene or chloroform, and...

Meshkova S. B., Z. M. Topilova, M. O. Lozinskii, D. V. Bolshoi. Periodicity of Variation of Stability-Constants of Lanthanide(III) Complexes with Fluorine Derivatives of Acetylacetone, Russ. J. Inorg. Chem., 40, 1296-1301 (1995). 

In studying the complexation of protactinium(IV) with acetylacetone, Lundqvist (1974) indicated that in solution the metal ion was present as PaO " (or equally PafOH) )- However, Lundqvist also noted that this behaviour was not present in other tetravalent metal ions such as Zr(IV), Hf(IV) or other actinide(IV) ions. As shown in Section 9.2.3, protactinium(V) exists as PaO ", a behaviour that is also not followed by other actinide(V) ions. The observations of Lundqvist (1974) differ from those of Guillaumont (1965, 1968) who indicated the formation of three protactinium(IV) hydrolysis species, PaOH, Pa(OH)2 and PafOHlg, with respective stability constants of log = -0.14, log 2 = -0.52 and log = -1.77 in measurements carried out in 3.0 mol 1 LiClO. Given that there are no supporting data for either of these interpretations, no data are retained for protactinium(IV). 

Lundqvist, R. (1974) Aqueous chemistry of protactinium(IV). Stability constants for Pa(IV)-acetylacetone complexes. Acta Chem. Scand., 28A, 243-247. 

The addition of comparatively less polar alcohols to solutions of acetylacetone in water shifts its keto/enol equilibrium in favour of the less polar m-enolic form (4b), which has been quantitatively rationalized in terms of so-called pairwise solute/solvent interactions [245], The keto/enol equilibrium of ethyl acetoacetate and acetylacetone has also been studied in polar supercritical fluids such as CHF3 (//= 1.65 D) and CCIF3 [fi = 0.50 D) [246], In polar trifluoromethane, the dipolar keto form was found to be favoured, although the change in the equilibrium constant with increasing sc-fluid density [i.e. increasing pressure) was quite minor. For ab initio calculations of the relative stabilities of various enols of acetylacetone in the gas phase, and theoretical calculations of keto/enol equilibria in aqueous solutions, see references [247] and [248], respectively. 

Despite its limited crystal field stabilization, the d complex bis(4-chloroben-zenethiolato)bis(l,2-bis dimethylphosphino ethane)technetium(II), (20), undergoes relatively slow trans to cis isomerization, with a rate constant of 1.6 x s in dichloromethane at ambient temperature. The low-spin d complex [Tc(acac)3] shows a similar reactivity with respect to exchange with " C-labeled acac to [Cr(acac)3]. Activation parameters for the technetium complex are AFT = 119 kJ mol" and A5 = -27 J mol" in acetylacetone. ... 

The comparison of the reported data for colour L, colom b and I. V. shows again that PBT 4, synthesized in the presence of Ti(0- Bu)4 / acetylacetone, is the most stable. All the other catalytic systems influenced negatively the stability of PBT even if Ti(0- Bu)4 is the worse. However, there are significant differences among the several catalysts on PBT properties. These effects are probably related to the strength of the complexes formed between Ti(lV) and the complexing agents. In particular it should be noted that Ti(0- Bu)4 / ethylacetoacetate is less deleterious in this case we noted a constant level of colour L, and the decrease of TV. and color b was less pronounced than in the other cases. 

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