Complex stepwise stability constants

I.r. and X-ray-induced photoelectron spectra of the complexes [M4(OH)g-(NH3CH2C02)8]Xg,12H20 (M = Zr or Hf X = Cl, Br, or NO3) have shown that the glycine molecules are O-bonded to the metal atoms. " A similar conclusion has been deduced from i.r. spectral studies of the Zr40(0H)g-(NH3CH2C02) ,(14 — n)H20 (n = 4—12) complexes. Stepwise stability constants have been reported for the complexes of zirconium(iv) with diphenyl-amine-2,2 -dicarboxylic acid, asparagine, and gjutamine. ... 

The stability of a complex is conveniently expressed in terms of the thermodynamic stepwise stability constant K as defined in Eq. (8.1). 

Stepwise stability constants decrease regularly in the normal manner 178), log > log K2 > log K, as may be exemplified by the values for the Ni -maltolate system, viz. 5.5, 4.3, and 2.7, respectively 179). Stability constants (log Kf) for a selection of 3-hydroxy-4-pyranonate and 3-hydroxy-4-pyridinonate complexes of some first-row transition metal 2+ cations are listed in Table IV 10,128,180—184). The values for the 3d transition metal cations conform to the long-established Irving-Williams order... 

Stepwise Stability Constants for the Formation of 3-Hydroxy-4-pyranonate Complexes... 

The stepwise stability constants for zirconium and hafnium thiocyanato-complexes have been determined by solvent-extraction techniques. The values ) i = 12.1 2.2, = 215 11, P4. = 205 + 20 for zirconium, and Pi =... 

The stepwise stability constants for V complexes with glutamic, aspartic, W -ethylenediaminedisuccinic, and W -ethylenediamine-bis-(a-glutaric acid) have been reported.The 1 1 oxovanadium(iv) complex of 5-nitrosalicylic acid has been characterized = 710 nm), and the mixed species formed between vanadium(iv) with protocatechuic acid (H3L ) or gallic acid (H L ) and 4-aminoantipyrine (aant) have been identified spectroscopically as the 1 1 1 and 1 2 2 HL (HL ) aant complexes. The species present in solutions of and tartaric acid below pH 2 have been identified as [VO-... 

Platinum(iv).—Group VII Donors. Simple syntheses of hexafluoro-complexes of some noble metals have been reported, including K2[PtF ]. The method involved the melt reaction between KHFj and K2[PtXg] (X = Cl, Br, or I), which has the advantage of not requiring corrosive reagents such as fluorine or BF3- The stepwise stability constants K have been measured for the bromoaquo-complexes [PtBr , (H20)-7 ] "" (n = 4, 5, or 6) formed in... 

Fig. 11.50 Stepwise stability constants. K,. K+ and Ky for ettiylenediamne complexes of several first-row transition metals in aqueous solution.

Table 39 Stepwise Stability Constants of some Six-coordinate Nickel(II) Amino Complexes...

Stepwise stability constants for complexation between Zn2+ and Cd2+ and the acids X(CH2CH2C02H)2 (X = 0, S, Se or Te), Se(CH2C02H)2, X(CH(Me)C02H)2 (X = S or Se) and H02CCH2SCH2CH2C02H have been measured.882 The structures of benzeneselenic acid complexes of zinc, cadmium and mercury have been investigated by IR spectroscopy the bonding of the areneseleninato ligand depends on the water content of the compound. The hydrated complexes are always of the 0,0-type the anhydrous complexes are mainly 0,0... 

A series of papers describe solution studies on nickel(II) complexes of aminoalkyltetrazoles (62, 63, 122). Stepwise stability constants for... 

Narula and Gupta76 have measured the thermodynamic stepwise stability constants for the formation of complexes of dialkyltin(TV) ions, R2Sn2+ (R = Me or Bu ), with hydroxamic acids, RCONHOH (R = Ph, Me2CH, Me) potentiometrically in 75% dioxane-water media. This has been followed by determination of formation constant of Af-arylhydroxamic acids-dialkyltin(IV) ions.77... 

Vanadium(m) forms more stable complexes with NCSe- ion in acetone and methyl cyanide than in DMF.383 Spectroscopic detection of the 1 3 and 1 2 complexes in acetone, the 1 2 complex in methyl cyanide, and the 1 1 complex in all three solvents has been achieved. Stepwise stability constants of the complexes are reported as are their electronic spectral parameters. V(antipyrene)3(NCSe)3 and V(diantipyrrylmethane)(NCSe)3 have been isolated from ethanol solutions. 

Table 5 Stepwise stability constants (logioX ) for formation of a selection of Zn + complexes, in aqueous solution at 298.2 K ...

Ion exchange data indicated the presence of two complexes of the trivalent ion, Pu(S04)" " and Pu(S0i )2, with respective stepwise stability constants of 44.7 and 43.7 at I = 2 M and 25° (12). It is unlikely and K2 would have such similar values, and hence K2 must be regarded with suspicion. Because these values were the same in both 1 M and 2 M HClOi, it was concluded that no proton-ated species were formed. This value of takes precedence over... 

Numerous determinations have been made of the stability constants of sulfate complexes of plutonium(IV), and the results vary by three orders of magnitude. The most plausible values (14) have come from careful ion exchange studies at I = 2 M and 25°, which indicate the presence of two species, Pu(S0i+) and Pu(S0i )2, with stepwise stability constants of 6.6 X 10 and 5.8 X 10, respectively. This Ki is in satisfactory agreement with the value 4.6 X 10 obtained potentiometrically at I = 1 M and 25° ( ). Spectrophotometric and electrophoretic studies indicate that plutonyl(VI) forms complexes containing as many as four sulfate groups, with anionic species predominating at sulfate concentrations above 1 M (15). The monosulfato complex has a reported stability constant of 14.4 as determined by extraction studies at I - 2 M and 25° (16). 

Stepwise stability constants for complex formation between Al111 of In111 and I-asparagine or l -glutamine have been evaluated from potentiometric data.388... 

The most substantial investigation of thallium(II) species in aqueous solution is that of Dodson and Schwarz, who studied equilibria and kinetics of Tl(II)-Cr complexes (77). On the basis of some (reasonable) assumptions, they have calculated the stepwise stability constants K for the three T1C1 " complexes, n = 1,2,3, in 1M HCIO4 and estimated = 1 from the ratios between the stability constants K, for Tfi Cl " and TT C1 ". The absorption spectra of the individual Tl(II) chloride complexes have been derived from their stability constants in combination with the experimental spectra recorded for solutions with varying composition. Absorption maxima were found at 263 and 342 nm for TlCl, at 280 and 342 nm for TICI2, and at 304 and 362 nm for TlCla". An interesting observation was the 10-fold increase of the extinction coefficient (at —340 nm) of the Tl(II) solution in 1 M perchloric acid upon addition of a small amount of chloride ion ([Cl ] = 10 M) (77). 

These spectral features and other evidence presented in this paper (97) leave no doubt that the Tl(III) cyano complexes exist, that they have the stated composition, and that they are extremely strong and kinetically inert. In fact, the cyano complexes are stronger than any other known monodentate complexes of thallium(III). The only possible known competitor as a ligand, the iodide ion, forms the complex TII4 with the overall stability constant log = 35.7 (99), i.e., several orders of magnitude lower than that of T1(CN)4" (see Table III). The distribution of thallium among the various Tl(CN), "-species is shown in Fig. 5. Stepwise stability constants of MX complexes often decrease with increasing n because of statistical, steric, and coulombic factors... 

In the formation of a complex [MLgf from [M(H20)g], each displacement of a coordinated water molecule by ligand L has a characteristic stepwise stability constant, K, Ki, K, K K, or Kfi. 

Figure 6.11 shows that for the formation of the complex ions [Al(H20)g xFx] (x = 1-6), the stepwise stability constants become smaller as more F ligands are introduced a similar trend is also observed in the formation of [Ni(H20)g x(NH3)x] (x = 1-6) in worked example 6.6. This decrease in values of K is typical of many systems however, the trend is not always as smooth as in Figure... 

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