Formates, metal, hydrates, dehydrations

There have been many instances of examination of the effect of additive product on the initiation of nucleation and growth processes. In early work on the dehydration of crystalline hydrates, reaction was initiated on all surfaces by rubbing with the anhydrous material [400]. An interesting application of the opposite effect was used by Franklin and Flanagan [62] to inhibit reaction at selected crystal faces of uranyl nitrate hexa-hydrate by coating with an impermeable material. In other reactions, the product does not so readily interact with reactant surfaces, e.g. nickel metal (having oxidized boundaries) does not detectably catalyze the decomposition of nickel formate [222],... 

The hydration rate constant of C02, the dehydration rate constant of carbonic acid (H2C03), and p pK2 values (pTf, =6.03, pTf2 = 9.8 at 25 °C, 7=0.5 M) (63) are such that nearly 99% of dissolved carbon dioxide in water at pH < 4 exists as C02. However, these four different species may be considered as the reactive species under different pH conditions which can react with aqua metal ions or their hydroxide analogues to generate the metal carbonato complexes. The metal bound aqua ligand is a substantially stronger acid than bulk H20 ( )K= 15.7). Typical value of the p of H20 bound to a metal ion may be taken to be 7. Hence the substantial fraction of such an aqua metal ion will exist as M-OH(aq)(ra 1) + species at nearly neutral pH in aqueous medium. A major reaction for the formation of carbonato complex, therefore, will involve pH controlled C02 uptake by the M-OH(" 1)+ as given in Eq. (17). 

Formation of M-O-M bonds in the hydrolysis products may proceed in two different ways. The first way is the typical process of aging of hydrated oxides their central metal atoms are coordinated by hydroxo-, oxo-, and aqua-groups. Dehydration of such product results in irregular amoiphous oxide structures, such as... 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

Two main types of complexes may be formed between metal ions and HSs (1) inner-sphere complexes, resulting in the formation of bonds with some covalent character between the ligand atom(s) and the metal ion, both completely or partially dehydrated and (2) outer-sphere complexes, resulting in electrostatic attraction between the ligand(s) and the metal ion that remains completely hydrated. 

On the other hand, although the formation of carbonyls with Fe, Ni and Co is very common, it does not occur when PFSA films exchanged with their aquated Fe+, Ni, Co+, Co+, or Cu+2 ions are reacted, either hydrated or dehydrated, with CO in the 0.1 to 1.0 atm and 25°C to 220°C range (15). It seems clear that reduction of these ions is required prior to carbonyl formation. While that fact is well known in metal carbonyl synthesis, it isn t entirely clear why such reduction is necessary in this ionomer since a wide range of other metal ions in PFSA do form carbonyls. In some of these cases it may be that the hydration of the ions is too strong for the CO to displace H2O to form a relatively weak association. In other cases the reduction may simply require more of a driving force than can be provided by the H2, which is formally or actually formed in the films through reaction of CO and H2O. 

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