Iodide complexes

Mcrcuryill) iodide, HgL. Scarlet (to 126 C) or yellow substance (HgC L solution plus KI or Hg plus I2)- Forms complex iodides with excess iodide (Nessler s reagent). 

The most extensively studied rate processes in this group are those which yield spinels [1] (ferrites, chromites, etc.), molybdates and tungstates, and complex iodides. These types are conveniently exemplified by the representative systems... 

An important characteristic feature, common to all these reactions, is the formation of a single product (barrier) phase. In addition, the lattice structures of both reactants and products are relatively simple and information on appropriate physical and chemical properties of these substances is available. Complex iodide formation is of particular interest because of the exceptionally large cation mobilities in these phases. Experimental methods have been described in Sect. 1 and Chap. 2. 

The complexation of anionic species by tetra-bridged phosphorylated cavitands concerns mainly the work of Puddephatt et al. who described the selective complexation of halides by the tetra-copper and tetra-silver complexes of 2 (see Scheme 17). The complexes are size selective hosts for halide anions and it was demonstrated that in the copper complex, iodide is preferred over chloride. Iodide is large enough to bridge the four copper atoms but chloride is too small and can coordinate only to three of them to form the [2-Cu4(yU-Cl)4(yU3-Cl)] complex so that in a mixed iodide-chloride complex, iodide is preferentially encapsulated inside the cavity. In the [2-Ag4(//-Cl)4(yU4-Cl)] silver complex, the larger size of the Ag(I) atom allowed the inner chloride atom to bind with the four silver atoms. The X-ray crystal structure of the complexes revealed that one Y halide ion is encapsulated in the center of the cavity and bound to 3 copper atoms in [2-Cu4(//-Cl)4(//3-Cl)] (Y=C1) [45] or to 4 copper atoms in [2-Cu4(/U-Cl)4(/U4-I)] (Y=I) and to 4 silver atoms in [2-Ag4(/i-Cl)4(/i4-Cl)] [47]. NMR studies in solution of the inclusion process showed that multiple coordination types take place in the supramolecular complexes. 

Example 2. A somewhat different method is illustrated by dissolving a little silver iodide in a solution of potassium iodide, the latter solution being considered as the solvent. This solution is then poured into a large excess of pure water which breaks up the complex iodide and produces colloidal silver iodide. 

A complex iodide having the formula CsI,AuI3 is produced in glistening, black crystals by the interaction of gold dichloride and caesium iodide.1... 

The electrochemical incorporation of CO2 into perfluoroalkyl derivatives has been explored in the case of (perfluoroalkyl)alkyl iodides and (perfluoroalkyl)alkenes, with an electrochemical system based on the use of consumable anodes combined with organometallic catalysis by nickel complexes. Iodide derivatives have been functionalized to the corresponding carboxylic acids by reductive carboxylation. Interesting and new results have been obtained from the fixation of CO2 into perfluoroalkyl olefins. Good yields of carboxylic acids could be reached by a carefull control of the reaction conditions and of the nature of the catalytic system. The main carboxylic acids are derived from the incorporation of carbon dioxide with a double bond migration and loss of one fluorine atom from the CF2 in a position of the double bond. 

The partly ionic, complex iodide salts discussed in the next section did show far higher conductivity, as expected from the elementary considerations in Section 2.2. 

Furthermore complex iodides of cadmium and mercury seem to be formed . It is very likely that sulphur dioxide will be a useful medium for the preparation of a number of bromo- and iodo-complexes which are not obtained from aqueous solutions. It is, however, neccessary to exclude traces of moisture, which in the presence of iodide ions might promote the occurrance of undesired redox reac-tionsi . It appears that sulphur dioxide offers many more possibilities as a medium for the preparation of various inorganic complex compounds. 

Due to the high donor properties of the solvent molecules halide ion-transfer reactions are limited in solutions of dimethyl sulphoxide. Although in the system C0CI2—TiCU chloride ion transfer gives in acetonitrile Co++ and [Tide]" and in trimethylphosphate [CoCla]" and [TiCla], no halide transfer is observed in dimethyl sulphoxide Complex iodides and complex bromides of class (a)... 

On the other hand class (b) metal iodides are unionized even in solvents of high donor number because the metal-iodine bonds are considerably stronger than the metal-solvent bonds, and they are capable of accepting iodide ions in such solvents. It is therefore possible to produce complex iodides of class (b) elements in solvents of high donor number by providing iodide ions. Gaizer and Beck ... 

It may be expected that many other complex iodides can easily be obtained by this method. However, in concentrated solutions, which do not obey Beer s law, heteropolynuclear species appear to be formed. ... 

ASS Low Polyphosphates, oxanions, EDTA complexes, metal cyanide complexes, iodide, thiosulfate, thiocyanate... 

The direct use of [Fe(a,a -dip)3]Ig solution containing an excess of 1 ions as precipitant for cadmium is interfered with by those metal ions which form slightly soluble or complex iodides. Solutions of Ag, Tl, or Pb salts may be precipitated by the iodide in the reagent and the precipitates are made red by adsorption of pF e(a,a -dip)3]+2 ions. Cu+ ions in neutral or acid solution liberate iodine forming CU2I2, which likewise combines wdth a,a -dipyridyl to form colored addition products. Hg, Sn, Sb, and Bi salts form soluble complex iodides which also yield red precipitates with [Fe(a,a -dip) 3]+ ions, although the sensitivity is less in these cases. 

Emetine and bismuth iodide. The B.P, standardises this complex iodide on its emetine and bismuth contents. 

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