Stability of Metal Complex

1 Stability of Metal Complex. - The stability of the metal complex towards ligand exchange reaction plays a major role in determining the mechanism by which the metal complex becomes anchored to the surface. The ligand exchange mechanism for anchoring the metal complex to the surface proceeds as 

2 Surface Acidity/Basicity. - Van Veen and co-workers were one of the first groups to discuss the importance of surface acidity/basicity as it relates to the interactions that favor decorating metal oxide surfaces with certain metal complexes. We alluded to the acidity/basicity of the surface vide supra) in describing how a metal complex may become subject to a reaction with the surface. Van Veen, et al. were interested in decorating surfaces with a wide range of metal acetylacetonate complexes to include Pt and Pd precursors. They showed that metal complexes that were susceptible to attack by acids were likely to decorate the surface of an acidic surface oxide by loss of a ligand to form a firm attachment with the surface. 

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T. Murkami, K. Ise, M. Hayakawa, S. Kaniei, and S. Tagaki, Stabilities of metal complexes of mugineic acids and their specific affinities for iron (III). Chem. Lett. 2137 (1989). 

STABILITY OF METAL-COMPLEX DYES 5.7.1 Factors governing the stability of metal complexes... 

Introduction 231 Fundamental concepts 233 Electronic structure of transition-metal ions 235 Structural characteristics necessary for complex formation 240 Preparation of metal-complex colorants 248 Isomerism in metal-complex dyes 260 Stability of metal-complex dyes 261 Chromium-related problems in the mordant dyeing of wool 268 References 277... 

Irving H, Williams RJP (1948) Order of stability of metal complexes. Nature 162 746-747... 

Systematic study of the stability of metal complexes in nonaqueous systems and their reactivity with thiols, free radicals, etc., is required for a fuller understanding of their complex effects on the co-oxidation reaction. 

For some time coordination chemists were aware of certain trends in the stability of metal complexes. One of the earliest correlations was the Irving-V/illiams series of stability For a given ligand, the stability of complexes with dipositive metal ions follows the order Ba2+ < Sr2+ < Ca2+ < Mg2+ < Mn2+ < Fez+ < Co2+ < Ni2+ < Cu"+ > Zn +. This order arises in part from a decrease in size across the series and in... 

As shown in Table 8 the stability of metal complexes of EDTA increases as the charge on the cation M"H increases and it is greater for transition metals than for the alkaline earths. If an element exists in more than one valency state, that in the higher oxidation state forms the more stable complex. The position of equilibrium in the reaction... 

In general, the stability of metal complexes of bidentate azomethines of the type (191) is comparable to that of metal complexes of the analogous bidentate azo compounds (14) and is inadequate for practical application in the dyestuffs field. Limited numbers of such complexes have, however, been claimed to be suitable for pigment applications. 

The stability of metal complex is also given by the number of chelate rings formed in the resultant ligand-metal complex. For example, desfer-rioxamine, the most widely used iron chelator, minimizes OH production by acting as a hexadentate ligand [Liu and Hider, 2002]. Unfortunately, there is not enough information on the denticity of polyphenols as metal chelators to assess the relevance of the stability of the flavonoid-metal complex formed. 

The significantly greater stability of metal-complexed NHCs relative to phosphines will permit further analysis of these fundamental reactions. Ongoing studies promise to provide significant insight into the aerobic oxidation of Pd(0) in Pd-catalyzed oxidation reactions. 

The effect of bulky ortho-substituted aza-aromatics on the stability of metal complexes depends mainly on the nature of the metal. In the case of com-plexation of Ag+ with methylpyridines, a Bronsted-type equation correlates with complexation AH with the pKa, indicating no direct steric effect to the approach of the Ag+ ion (74BSF2793). 

Irving, H. M. N. H. Stability of Metal Complexes, in International Conference on Coordination Chemistry, London, 1959 (Special Publication No. 13), 13-34, The Chemical Society, London (1959). 

The well known Irving-Williams series1253 2561 and the HSAB principle1257-1 are established empirical concepts related to the stability of metal complexes, and the question of whether these are accounted for in a general molecular mechanics approach have not always been appreciated when metal ion selectivities have been modeled via empirical force field calculations. The assumption that the position of the minima and the steepnesses of the potential energy functions for the metal-ligand bonds for varying metal ions and constant donor sets accurately reflect var-... 

Tantalum enolate chemistry shows the dichotomy for the carbonylation reaction " of Cp Ta(CH2R)Cl3 with CO which results in the mono-THF adduct of rj -acyl complex Cp Ta(0=CCH2R)Cl3(THF) for R = t-Bu (the acyl group is anionic) but the isomeric enolate Cp Ta((Z)-7j -OCH=CHR)Cl3 for R = p-Tol. This invites the question of the relative thermodynamic stabilities of metal complexes of RCH2CO and RCHCHO and additionally the question of Z vs. E enolate stabilities. Only for organometalhc compounds (X = [M]) do we find examples where RCH2COX is less stable than RCH=CHOX. 

Steric interactions between ligands can affect the stability of metal complexes and are especially important in complexes of the lanthanide ions. 

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