Chloride ion as ligand

Problem In order to intensify the idea of equilibrium and the dependence on temperature, cobalt complexes are useful with a mixture of water molecules and chloride ions as ligands for cobalt complexes the blue colored tetra chloro cobalt complex proves stable in heat, the pink colored hexa aqua cobalt complex in the cold solution, respectively. A cross-linkage to the idea of equilibrium (see Chap. 6) is possible. 

In the case of ionic liquids containing high amounts of halides, the chemical attack of the metallic oxides at the electrode surface occurs that means that only few metals are really inert in these media and consequently the anodic potential limit is governed rather by the metal oxidation. Even metals such as R, Au, A1 and Ti may be oxidized in ionic liquids and their oxides can be dissolved especially in eutectics containing chloride ions as ligands for metallic ions dissolution. This phenomenon allows the use of soluble anodes during electrodeposition procedure. 

The Ci bidentate ligand system may be as simple as a chiral monophosphine and a chloride ion, as shown in Figure 13.12. Suppose that in a P-X ligand system the nucleophilic attack takes place at the position trans to the phosphine, then we expect on the basis of micro reversibility that also the... 

Commercially available palladium compounds in the presence of various ligands have often been used as catalysts (Table 3-1). The first choice is often the air-stable and relatively inexpensive palladium acetate however, several of the other published variants can be preferable in certain applications. It is commonly assumed that the palladium(II) species is reduced in situ by the solvent, the alkene [11], the amine [12] or the added ligand (frequently a phosphane, which is oxidized to a phosphane oxide) [13]. In some cases, highly dispersed elemental palladium on charcoal can be applied. In the case of alkenyl or aryl bromides, phosphanes are necessary to avoid precipitation of palladium black (c.f., however. Section 3.2.4.), whereas iodides have been reported to be less reactive in the presence of phosphanes. Triflates have been found to be more reactive in the presence of chloride ions, as the chloride ligand is more easily removed from palladium than the tiiflate ion [14], However, this also has become questionable, because successful coupling reactions of alkenyl triflates have been performed in the absence of chloride ions [15]. 

When six ligands are attached to a central metal ion, Werner predicted an octahedral structure. Thus, for Co(NH3)5Cl3, he postulated a structure in which the five ammonia molecules and only one of the three chloride ions are ligands tightly bound to cobalt. The other two chloride ions are free in aqueous solution and readily precipitate with Ag. He termed such chemical species coordination compounds and identified six as the coordination number for Co. Further proof came from Werner s identification of cfr-(Cl-Co-Cl angle 90°) and trans- (Cl-Co-Cl angle 180°) isomers for Co(NH3)4Cl3, and the acmal isolation of enantiomers (see the structures depicted) in 1911. For this work, Werner received the Nobel Prize in chemistry in 1913. 

Setup (a) There are six ligands five NH3 molecules and one Cl ion. The oxidation state of cobalt is +3. making the overall chaige on the complex ion +2. Therefore, there are two chloride ions as counter ions. 

Halogens can act as ligands and are commonly found in complex ions the ability of fluorine to form stable complex ions with elements in high oxidation states has already been discussed (p. 316). However, the chlorides of silver, lead(Il) and mercury(l) are worthy of note. These chlorides are insoluble in water and used as a test for the metal, but all dissolve in concentrated hydrochloric acid when the complex chlorides are produced, i.e. [AgCl2] , [PbC ] and [Hg Clj]", in the latter case the mercury(I) chloride having also disproportionated. 

For this reaction, charcoal is a catalyst if this is omitted and hydrogen peroxide is used as the oxidant, a red aquopentammino-cobalt(lll) chloride, [Co(NH3)jH20]Cl3, is formed and treatment of this with concentrated hydrochloric acid gives the red chloro-p0itatnmino-coba. t(lll) chloride, [Co(NH3)5Cl]Cl2. In these latter two compounds, one ammonia ligand is replaced by one water molecule or one chloride ion it is a peculiarity of cobalt that these replacements are so easy and the pure products so readily isolated. In the examples quoted, the complex cobalt(III) state is easily obtained by oxidation of cobalt(II) in presence of ammonia, since... 

Attempts have been made to categorize the interactions between metal ions and ligands. Whereas all metal ions interact more strongly with fluoride than with chloride in the gas phase, in aqueous solution a number of exceptions occur. Metal ions that have the normal (class a) aqueous solution stabiUty order of F Cl > Br > I also have N P > As > Sb and 0 S > Se > Te donor stabiUty order (13). The inverse (class b) aqueous solution stabiUty... 

The utility of thallium(III) salts as oxidants for nonaromatic unsaturated systems is a consequence of the thermal and solvolytic instability of mono-alkylthallium(III) compounds, which in turn is apparently dependent on two major factors, namely, the nature of the associated anion and the structure of the alkyl group. Compounds in which the anion is a good bidentate ligand are moderately stable, for example, alkylthallium dicar-boxylates 74, 75) or bis dithiocarbamates (76). Alkylthallium dihalides, on the other hand, are extremely unstable and generally decompose instantly. Methylthallium diacetate, for example, can readily be prepared by the exchange reaction shown in Eq. (11) it is reasonably stable in the solid state, but decomposes slowly in solution and rapidly on being heated [Eq. (23)]. Treatment with chloride ion results in the immediate formation of methyl chloride and thallium(I) chloride [Eq. (24)] (55). These facts can be accommodated on the basis that the dicarboxylates are dimeric while the... 

The chloride ions that appear outside the brackets represent chloride anions that balance the positive charge on the coordination compound. When a coordination compound dissolves in water, the ligands (inside the brackets) remain bound to the metal cation, but the nonligands (outside the brackets) exist as individual ions. These chloride ions precipitate in the presence of silver ions. The chloride ions inside the brackets, which are ligands bonded to the cobalt center, do not precipitate as AgCl. 

---