Metals in complex anions

TABLE 25-6 Names for Some Metals in Complex Anions... 

Often, we need only a qualitative estimate that is, we want to know whether the limiting current is raised or lowered by migration relative to the purely diffusion-limited current, or whether a, is larger or smaller than unity. It is evident that a, will be larger than unity when migration and diffusion are in the same direction. This is found in four cases for cations that are reactants in a cathodic reaction (as in the example above) or products in an anodic reaction, and for anions that are reactants in an anodic reaction or products in a cathodic reaction. In the other four cases (for cations that are reactants in an anodic or products in a cathodic reaction, and for anions that are reactants in a cathodic or products in an anodic reaction), we have a, < 1, a typical example being the cathodic deposition of metals from complex anions. 

A simple and straightforward approach to their synthesis is the reaction between simple metal salts and the alkali metal or complex anion pseudohalides. Mixed ligand complexes can easily be made via addition of a neutral ligand to the anionic complex species (cf. preparation of trans-ML2(NCS)2, e.g. 103). However, all these methods have been well reviewed202 209 and representative examples can be found in the references of Section 13.5.5.3. 

For the electrodeposition of metals or alloys from air- and water-stable ionic liquids, it is necessary first to dissolve the corresponding metal ions in the ionic liquid. Such a dissolution process is made possible by introducing excess amounts of halide ions (such as Cl ) to form soluble metal-halide complex anions. Alternatively, the metal is dectrochemically oxidized in the ionic liquid to form the soluble salt such as Sn(Tf2N) in the trimethyl-n-hexylammonium [bis(trifluoromethyl)sulfonyl]amide ([TMHAj TfiN ) ionic liquid. 

Processes taking place in ionic melt-solvents are considerably affected by impurities contained in the initial components of the melt or formed during preparation (mainly, melting) of solvents due to the high-temperature hydrolysis of melts or their interactions with container materials (AI2O3, SiOj, etc.) or active components of atmosphere (O2, CO2, etc.). The list of these impurities is wide enough and includes multivalent cations of transition metals, different complex anions (0x0- or halide anions). The effect of the mentioned admixtures on the processes in ionic melts depends mainly on the degree of their donor-acceptor interactions with constituent parts of the melt. 

In this section we will consider the interaction of the nitro compound with the metal center, but we will not include the reaction of aliphatic nitro compounds when they interact with the metal in their anionic form [20], It is not the purpose of this book to review all of the complexes reported to contain a coordinated organic nitro compound, so only a general outline will be presented. Two reviews have already been published on the coordination chemistry of nitro [21] and nitroso [22] organic compounds, although both of them are now quite old. 

K. Liska and L. Klir "Use of Anion Exchangers in Analytical Chemistry. 1. Sorption of Chloride Complexes of Certain Metals in OAL Anion Exchangers" Chem. listy 51, 1467-70(1957) UCRL Trans. 536(L) (1960). 

Complexes which contain a transition metal in the anion may react with alkyl halides to yield <7-alkyl metal derivatives. Such anions are formed commonly by reduction of metal carbonyls or cyclopentadienyl metal carbonyls with sodium amalgam in tetrahydrofuran ... 

When naming complex ions the number and type of ligands is written first, followed by the name of the central metal ion. If the complex as a whole has a positive charge, i.e. a cation, the name of the central metal is written unchanged and followed by the oxidation state of the metal in brackets, for example [Cu(N 113)4] becomes tetra-ammine copper(II). A similar procedure is followed for anions but the suffix -ate is added to the central metal ion some examples are ... 

Aqueous solutions of caustic soda aie highly alkaline. Hence caustic soda is ptimatily used in neutralization reactions to form sodium salts (79). Sodium hydroxide reacts with amphotoric metals (Al, Zn, Sn) and their oxides to form complex anions such as AlO, ZnO. SnO ", and (or H2O with oxides). Reaction of AI2O2 with NaOH is the primary step during the extraction of alumina from bauxite (see Aluminum compounds) ... 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

---