Stability constants mixed ligand

It is important to note that although equation 7 can provide much greater calculated M,j,/[M] values than equation 1, It is, nevertheless, expected that equation 7 will provide underestimates of the total to free metal ratio. This conclusion is based on the observation ( 1) that equation 6, in the vast majority of cases, underestimates the magnitude of mixed ligand stability constants. 

In general, mixed ligand stability constants are larger, and often considerably larger, than predictions based on single ligand type stability constants, ( 1, 6). A simple example of this occurs... 

Experimental Examination of Mixed Ligand Stability Constants... 

The 2 results shown In Table III provide the following theoretically predicted mixed ligand stability constant ... 

The complexation of other mixed oxa aza macrocycles has been studied, and protonation and stability constants of the zinc complexes of macrocycles l,4,10,13-tetraoxa-7,16-diazacycloocta-decane-7,16-bis(malonate), the -7-malonate derivative and -7,16-bis(methylacetate) derivative have been determined by potentiometry at a 1 1 ligand-to-metal ratio.730... 

Solution equilibria of Fe(III)/Cr(III) in methionine and Fe(III)/Cr(III) in methio-nine/penicillamine complex systems were studied by paper electrophoresis and were reported by Tewari [38]. The formation of 1 1 1 mixed ligand complexes is inferred, and the stability constants of the complexes at 35 °C and 0.1 M ionic strength were 6.80 0.09 (Fe(III) methionine penicillamine) and 4.60 0.16 (Cr(III)-methionine-penicillamine), respectively. 

An electrophoretic method was described by Srivastava et al. [40] to study equilibria of the cited mixed ligand complex systems in solution. Stability constants of the Zn(II) and Cd(II) complexes were 5.36 and 5.18 (log K values), respectively, at an ionic strength of 0.1 and a temperature of 35 °C. 

An ionophoretic method was described by Tewari [41] for the study of equilibria in a mixed ligand complex system in solution. This method is based on the movement of a spot of metal ion in an electric field with the complexants added in the background electrolyte at pH 8.5. The concentration of the primary ligand (nitrilo-triacetate) was kept constant, while that of the secondary ligand (penicillamine) was varied. The stability constants of the metal nitrilotriacetate-penicillamine complexes have been found to be 6.26 0.09 and 6.68 0.13 (log K values) for the Al(III) and Th(IV) complexes, respectively, at 35 °C and an ionic strength of 0.1 M. 

The measurement of stability constants of complexes of yttrium, lanthanide, and actinide ions with oxalate, citrate, edta, and 1,2-diaminocyclohexanetetra-acetate ligands has revealed that there is a slight increase in the stability of complexes of the /-electron elements, relative to the others. A series of citric acid (H cit) complexes of the lanthanides have been investigated by ion-exchange methods and the species [Ln(H2cit)]", [Ln(H2cit)2] , [Ln-(Hcit)], and [Ln(Hcit))2] were detected. Simple and mixed complexes of dl- and jeso-tartaric acid have been obtained with La " and Nd ions, and the stability constants of lactate, pyruvate, and x-alaninate complexes of Eu and Am " in water have been determined. 

Given the structure of InF3-3H20 (see above) and the tendency of indium(III) to be six-coordinate with hard ligands, it is reasonable that the mixed fluoro/aqua anionic complexes should also be [InF4(H20)2] and [InF5(H20)]2. This is compatible with the evidence from aqueous solution chemistry, where stability constants and thermochemical results indicate a series of [In(H20)6-nFn]l3 n)+ species.9 These complexes still await detailed systematic structural investigation. 

Table 46 Stability Constants /SVOAL of Some Mixed-Ligand Chelates of Oxovanadium(IV)a...

Extension of the principle to more complex equilibria of the type OL(, and of mixed ligand complexes, etc. is straightforward. In conclusion, the stability constants of such complexes can be determined by means of any electrochemical technique that allows to determine E, 2. ... 

Mixed ligand complexes of Zn2+ with en and monoethanolamine (mea) in H20-MeOH systems have been investigated.192 At <20% MeOH, the presence of the complexes [Zn(en) —(mea)3 ]2+ (n = 0-3) and the complexes [Zn(en)2]2+ and [Zn(mea)2]2+ is indicated. At >20% MeOH, only the tris complexes (n = 0 or 3) are found. Stability constants for mixed complexes of Zn2+ with en and glycine in mixed aqueous solutions of methanol, dioxane, acetonitrile and DMF have been determined.193 In general, the stability constants increase with increasing composition of the co-solvent in the order H20 < MeOH < MeCN < DMF < dioxane. 

Mixed donor ligands. AG°, AH°, and AS° values for the formation of complexes between asparaginate and Mn2+ as well as H+, Fe2+, Co2+, Ni2 +, and Zn2+ in aqueous solution at 25°C have been reported.93 Cytostatic Hadacidin, JV-formyl-JV-hydroxyglycine (HAD), forms the complex Mn(HAD) for which spectroscopic and stability constant data have been reported.94 Manganese(n) complexes of human serum albumin have also been studied.95... 

It is useful to note that ac and n are functions of a only provided the system consists of a mononuclear complex. In the case of polynuclear complexes ac and h are dependent on both a and the concentration of M. When mixed complexes MA Lm are formed, ac and h are functions of concentrations of both ligands A and L. Thus it is necessary in any system to confirm that the experimental values of ac and n are functions of a only before calculating the stability constants. Once this condition is satisfied, N sets of values n, a or ac should be sufficient for the determination of N values of ... 

The sulfate MnS04 and its hydrates (7, 5, 4, 2 and 1) represent the stable oxidation state under ambient conditions. Compounds are colourless in finely-divided form and pale pink or rose coloured when crystalline. All appear to be examples of high spin octahedral Mn11. Aqueous solutions have been much studied, to define the physical parameters, because of their importance in Mn production from its ores. Stability constants for 1 1, 1 2 and 1 3 species have been defined but detail (structurally) of the labile Mn polyhedra is unclear. Examples of unidentate and bridging sulfato are seen in the known crystal structures, but not bidentate or terdentate to the same metal atom. (However, bidentate function may occur in some of the mixed-ligand compounds described earlier.)... 

Stability constant measurements have been undertaken to show that in basic solution mixed amino acid ligands with two amino acid moieties present, i.e. NH2—C(R)—C—N—C(R )— COOH), yield complexes with log K values of the order of 6 to 7 384 such compounds appear to bind the amine nitrogen.385... 

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