Chloro complexes stability

Explain in terms of redox chemistry how the (bnnatkni of chloro complexes stabilizes ihenium(llll... 

The level of soluble thallium present in the sea (e.g. Pacific Ocean, Atlantic Ocean, Irish Sea, Australian Coast) is between 9 and 16 ng/L (Matthews and Riley, 1970). This is remarkably lower than in fresh waters. In natural sea water (pH 8.1), the oxygen content is sufficient to oxidize Tl(l) to Tl(lll). because formation of chloro-complexes stabilizes the trivalent state. In the Pacific Ocean, 80% of the thallium was found to occur as Tl(lll), and only 20% as the sum of Tl(l) and alkylthallium compounds (Batley and Florence, 1975). As Tl(lll) is easily adsorbed and coprecipitated, it continuously moves down to the sediments. 

There is some uncertainty regarding the validity of the stability constants of chloro complexes of Mn according to other computations Mn is a major inorganic species. 

Ruthenium(m).—Group VII Donors. The consecutive stability constants Ky—Kj of chloro-complexes of Ru have been determined in aqueous and aqueous-alcoholic 1N-HC104. Other Russian workers have compared the... 

Chloro complex Thermal stability of 2—substituted dimeric tr-allyl-Ni—X complexes in 0.05 molar toluene solution (dec. temp, in °C). 

The chloro complex CrCl(TPP) is a non-electrolyte in DMSO and neutral N, O and S donor ligands will bind to give six-coordinate species.1255 There is little difference in the stability... 

For cis-diarnmmedichloroplatinum(Il) to work according to the proposed mechanism. it must hydrolyze In the right place t it hydrolyzes in the blood before it gets to the chromosomes within the cell, it will be more likely to react with a nonlurget species. Fortunately for the stability of the complex, the blood is approximately 0.1 M in chloride ion, forcing the hydrolysis equilibrium (Echloro complex. Once the drug crosses the cell membrane into the cytoplasm, it finds a... 

We shall consider reactions catalysed by two different types of pro-catalyst the first (type A) employs Pd-allyl cations ([Pd(a]lyl)(PCy3)]+/Et3SiH or [Pd(allyl)(MeCN)2] + ), and the second (type B) employs Pd-alkyl or chloro complexes ([(phen)Pd(Me)(MeCN)]+, where phen = phenanthroline, and [(RCN)2PdCl2]). These two types of catalysts give very different products in the cyclo-isomerisation of typical 1,6-dienes such as the diallyl-malonates (10), Scheme 12.6. Since there is known to be a clear order of thermodynamic stability 11 < 12 <13, with a difference of ca. 3-4 kcal mol 1 between successive pairs, any isomerisation of products under the reaction conditions will tend towards production of 12 and 13 from 11 and 13 from 12. Clearly, when 11 is the major product (as with pro-catalysts of type A), it must be the kinetic product (see Chapter 2 for a discussion of kinetic and thermodynamic control of product distributions). However, when 12 is generated selectively, as it is with pro-catalysts of type B, there is the possibility that this is either generated by rapid (and selective) isomerisation of 11 or generated directly from 10. 

A model for such a reaction sequence is (21-XLIV).184 In the case of Pd11 complexes of rigid bidentate nitrogen ligands, products of multiple successive insertions of alkenes and CO have proved isolable.185 The insertion of an alkene into the Pd—acyl bond of a neutral acyl chloro complex leads to displacement of the halide ligand and formation of a chelate-stabilized product (21-XLV).186... 

The situation becomes more complicated if a given ionization reaction is studied in solvents that differ both in their EPD and EPA properties. This may be illustrated for the complex formation between Co and Cl ions. Qualitatively, stabilities of cobalt-chloro complexes usually decrease with increasing EPD strength of the solvent (25, 26). Quantitative measurements reveal, however, a number of irregularities which cannot be understood by considering the differences in solvent donicities. Accurate thermodynamic data have recently been determined for the reaction... 

For example, complexes with very strong EPD ligands, such as Ng ", NCS ", CN, or F may exist even in solvents of high DN such as HMPA or DMSO. In solvents of weak or medium EPD properties, complex formation is essentially quantitative. On the other hand, bromo and iodo complexes usually exist only in weak EPD solvents, such as NM, PDC, or AN, and are completely ionized in solvents such as DMF, DMSO, or HMPA. The stabilities of chloro complexes are somewhat higher in the respective solvents. According to Table VII the chloride ion has an EPD strength similar to that of DMF or DMSO. Consequently chloro complexes in these solvents (compare Table IV) are ionized to some extent, sometimes with autocomplex formation. 

Because mercury forms relatively stable hydroxo, sulfato, and chloro complexes in solution, the solubilities and relative stabilities of mercury minerals depend heavily on ambient solution compositions. Figure 4 illustrates the calculated effect of pH and total sulfate on the solubility of schuetteite. The curves take into account all complexes for which data are available in Martell and Smith (18) and precipitation of HgO they cross when changes in solution composition result in changes in dominance among complexes. Schuetteite is quite soluble relative to HgS and elemental mercury under common conditions. 

Currently, GEOCHEM includes estimated stability constants of hydroxy-chloro complexes of a few trace metals. Lack of data on many mixed-ligand complexes is clearly one of the significant shortcomings in modeling studies at present. 

Where the central metal ion is small the fluoro-complexes are less stable in solution than the chloro-complexes, perhaps because appreciable jr-bonding is possible only in the latter. The complex fluorides of base metals with large positive ions are more stable than the corresponding complex chlorides. Hydration energies also play a part in determining relative stabilities in solution. The complex fluorides may be grouped into several structural types ... 

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