Complex formation equilibria halide complexes

Halides other than fluoride form very weak complexes in aqueous solution there are no reliable equilibrium constants to be found in the literature. The solution chemistry of aqueous solutions of beryllium chloride, bromide, and iodide have been reviewed previously (9). Some evidence for the formation of thiocyanate complexes was obtained in solvent extraction studies (134). 

Much work has been devoted to the halide complexation of these elements in non-aqueous media. Equilibrium and calorimetric measurements for the formation of the [MX ](n-2) (M = Zn or Cd X = Cl, Br, I or SCN n = 1-4) anions in dimethyl sulfoxide (DMSO) have shown that stability constants follow the same order, but are much larger than those found for aqueous solution zinc exhibits an enhanced hardness as an acceptor in DMSO as compared to cadmium. Calorimetric measurements indicate a change from octahedral to tetrahedral coordination with increasing halide concentrations.1002-1006... 

Ammonia complexes.. EflFect of complex formation on solubility. Cyanide complexes. The cyanide process of treating gold and silver ores. Complex halides and other complexes. Sodium thiosulfate as photographic fixer. Hydroxide complexes. Amphoteric hydroxides. Sulfide complexes. Equilibrium expressions for complex formation. Structural chemistry—tetrahedral, octahedral, square complexes. Existence of isomers. 

Reagents that form insoluble Hg(II) salts or stable Hg(II) complexes upset equilibrium 22.167 and decompose Hg(I) salts, e.g. addition of [OH] , or [CN] results in formation of Hg and HgO, HgS or [Hg(CN)4], and the Hg(I) compounds Hg20, Hg2S and Hg2(CN)2 are not known. Mercury(II) forms more stable complexes than the larger [Hg2] and relatively few Hg(I) compounds are known. The most important are the halides (22.89). Whereas Hg2p2 decomposes to Hg, HgO and HF on contact with water, the later halides are sparingly soluble. 

Reversal correlates with the presence of lithium ion and also with the involvement of betaine species. These two risk factors are interrelated because lithium halides rapidly cleave oxaphosphetane 31 or 32 (Scheme 8) at — 70°C resulting in the reversible formation of the betaine lithium halide complexes 40 or 41, respectively (18b). Donor solvents shift the equilibrium toward the oxaphosphetane by coordinating the lithium halides and thereby promote stereospecific decomposition to the alkenes. If the solvent is not an effective lithium coordinating agent, then 40 and 41 decompose slowly, and the risk of... 

The equilibrium between a- and ti-allyl complexes can be influenced by the ligands. Thus strongly basic alkyl phosphine ligands favor the a structure, as has been shown for allyl metal halide complexes of Pt and Ni Soft Jt-acceptor ligands such as CO favor the formation of it-allyl complexes. 

The stereochemical transformation of the mercury halide complexes in the course of the stepwise complex formation could also be followed by means of X-ray examinations [Ga 68]. The results at times cast doubt on the correctness of the conclusions derived from the equilibrium data. In the case of mercury halides, the stability of the third stepwise-formed complex is much higher than that of the fourth, and the value of X3/X4 is therefore large. This would indicate that the former complex already has tetrahedral symmetry. According to the X-ray examinations, however, the reason for the anomalous stability sequence is that the second complex is linear, the third is pyramidal and only the fourth has tetrahedral symmetry [Ga 68]. 

The halide alkanes when used as HA perturbers make the system easily turbid under excessive amount. This makes the studying of inclusion equilibrium more difficult. While the halide alcohol perturbers, for example, 2-bromoethanol and 2,3-dibromopropanol, participating in the formation of inclusion complex as water-soluble third component is more favorable. First, Hamai [44] and sequentially Spanish researchers [45-47] reported the relevant results. 

In aqueous solution, the complexes of most metal cations exist in dynamic equilibrium with their components. If we disturb this equilibrium, another one is instantly formed. It is quite otherwise with robust complexes which persist for hours (or even days) under conditions favourable to their decomposition any biological properties that they may have are strikingly different from those of their components. Robust complexes are formed where metal ions have 3,4 (low spin), 5, or 6 d electrons provided that formation of the complex involves large values of ligand-field stabilization energy. Metals most prone to form robust complexes are the transition metals platinum, iridium, osmium, palladium, rhodium, ruthenium, also (but not so frequently) nickel, cobalt, and iron. The halide and, particularly, the cyanide anions most readily form robust complexes with these transi-... 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

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