Halides solution chemistry

John D. Corbett once said There are many wonders still to be discovered [4]. This certainly holds generally for all the different areas and niches of early transition cluster chemistry and especially for the mixed-hahde systems. The results reported above so far cover a very Hmited selection of only chloride/iodide systems and basically boron as the interstitial. Because of the very sensitive dependence of the stable stracture built in the soHd-state reaction type on parameters like optimal bonding electron counts, number of cations present, size and type of cations (bonding requirements for the cations), metal/halide ratio, and type of halide, a much larger mixed-hahde cluster chemistry can be expected. Further developments, also in mixed-hahde systems, can be expected by using solution chemistry of molecular clusters, excised from solid-state precursors. 

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). 

Almost all of the reactions that the practicing inotganic chemist observes in the laboratory take place in solution. Although water is the best-known solvent, it is not the only one of importance to the chemist. The organic chemist often uses nonpolar solvents sud) as carbon tetrachloride and benzene to dissolve nonpolar compounds. These are also of interest to Ihe inoiganic chemist and, in addition, polar solvents such as liquid ammonia, sulfuric acid, glacial acetic acid, sulfur dioxide, and various nonmctal halides have been studied extensively. The study of solution chemistry is intimately connected with acid-base theory, and the separation of this material into a separate chapter is merely a matter of convenience. For example, nonaqueous solvents are often interpreted in terms of the solvent system concept, the formation of solvates involve acid-base interactions, and even redox reactions may be included within the (Jsanovich definition of acid-base reactions. 

The solution chemistry of zinc and cadmium halides is a topic of active interest, and numerous studies of the related equilibria shown in Scheme 3, in various solvents S, have been reported. 

In Section 4.4, finally, troublesome aspects are shortly summarized. An important aspect is that the electrochemical window alone is not sufficient and one can be pretty surprised if the electroreduction of e.g. TaCls rather delivers non-stoichiometric halides instead of the desired tantalum metal. For an electroplating bath the solution chemistry also plays an important role and a new concept of additives seems to be necessary. 

Progress in the Science and Technology of the Rare Earths, Vol. 1,1964. (A continuing series with reviews on extraction, solution chemistry, magnetic properties, analysis, halides, oxides, and so on.)... 

The lower nuclearity clusters [Mo5Cl13]2 were isolated from MoCls in AlCl3/KCl/BiCl3/Bi melts that led to the hexanuclear species (17). This is the only intermediate isolated from reaction mixture that produces the Mo6C18 4+ core. Solution chemistry has yielded Mo2, Mo3, and Mo4 halide species from mononuclear molybdenum complexes, suggesting that a nucleation process similar to that proposed for the tungsten systems may take place during the formation of hexanuclear molybdenum clusters (18-22). 

Octahedral clusters of the electropositive metals, groups 3 to 7, are stabilized by 7r-donor ligands such as halides, chalcogenides, and alk-oxides, but the majority accessible to solution chemistry are the halide complexes. These highly s5Tnmetric and aesthetically pleasing MeYs " and clusters contain a robust core of six metal... 

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