Ammonia bonding

Luteocobaltic chloride (modern, [Co(NH3)6]C13, hexaamminecobalt(III) chloride) is a stable yellow-orange compound.55 In solution, all the chlorine is immediately precipitated by silver nitrate. Treatment with hydrochloric acid at 100 °C does not remove any ammonia. Treatment with sulfuric acid does not remove any ammonia, but yields the compound Co2(S04)3T2NH3, i.e. the chlorine atoms are replaced by sulfate groups. Clearly, some sort of very stable metal—ammonia bonding but much less stable metal—chlorine bonding is indicated. 

A study82) of ammonia hemi-hydrate, whose resonance frequencies are not very different from those of ammonia, supports the view that hydrogen bonds linking ammonia to water molecules are not very different from ammonia-to-ammonia bonds. 

Evangelou, V. P. 1989a. Chemical mechanisms regulating ammonia bonding with various salts in the crystal form and field implications. Soil Sci. Soc. Am. J. 54 394-398. 

A different type of catalyst is conshtuted by Co ion-exchanged zeolites and mesoporous materials (MCM-49). Co-ZSM-5 was found to be selective in ethane ammoxidation [135]. A good correlahon between the acidity and the catalytic activity was observed. The strength of ammonia bonding to the catalyst appears to have a crucial effect on the activity of Co-ZSM-5. Li and Armor [136] reported that dealuminated zeolite was achve for the ammoxidation of ethane to acetonitrile. Pan and coworkers [137] instead studied ion-exchanged Co-Na-MCM-49 and Co-H-MCM-49 materials for the same reaction, reporting that the presence of ammonia in the feed considerably improved the selectivity and total yield of ethylene and acetonitrile. 

Scheme 7. Enthalpies (kcal mor ) of formation and Si-Si bond cleavage reactions of some coordinated disilenes, calculated at the B3LYP/6-31 l+G //B3LYP/6-31 l+G level values in parentheses refer to the reaction enthalpy of the formation of the coordinated disilene from disilene and 1 or 2 molecules of ammonia bond lengths in pm.

The father of modern coordination chemistry was Alfred Werner, who was born in 1866 and lived most of his life in Zurich. At the time it was known that the oxidation of cobalt(II) (cobaltous) salts made alkaline with aqueous ammonia led to the formation of cobalt(III) (cobaltic) salts containing up to six ammonia molecules per cobalt atom. These ammonia molecules were evidently strongly bonded because very extreme conditions— boiling sulfuric acid, for example—were needed to separate them from the cobalt. There had been considerable speculation about the cobalt-ammonia bonding and structures such as... 

Alkali promoters can also inhibit ammonia adsorption. In the case of magnetite catalysts there is indirect evidence that this is caused by neutralization of the acidic alumina phase. A similar effect is also observed on alumina-supported transition metals. ESCA evaluation of ruthenium catalysts demonstrated a significant increase in the ammonia bonding on alumina supports that could be reversed in the presence of alkali promoters. This is also apparent from the marked changes in the reaction order in ammonia for ruthenium on a variety of acidic and basic supports (Table 9.7). However, recent surface-science studies (discussed in detail in Chapter 5)... 

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