Chloride-ammonia coordination

The complexes of copper(I) like those of silver(I) (p. 430), but unlike those of preceding transitions metals, tend to prefer a linear coordination of two ligands, i.e. X—Cu—X thus copper(I) chloride in aqueous ammonia gives the colourless [Cu(NH3)2] (readily oxidised in air to give blue [Cu (NH3)4(H20)2] copper(I) chloride in hydrochloric acid gives [CuClj], although [CuCl3] is also known. 

Ammonia forms a great variety of addition or coordination compounds (qv), also called ammoniates, ia analogy with hydrates. Thus CaCl2 bNH and CuSO TNH are comparable to CaCl2 6H20 and CuSO 4H20, respectively, and, when regarded as coordination compounds, are called ammines and written as complexes, eg, [Cu(NH2)4]S04. The solubiHty ia water of such compounds is often quite different from the solubiHty of the parent salts. For example, silver chloride, AgQ., is almost iasoluble ia water, whereas [Ag(NH2)2]Cl is readily soluble. Thus silver chloride dissolves ia aqueous ammonia. Similar reactions take place with other water iasoluble silver and copper salts. Many ammines can be obtained ia a crystalline form, particularly those of cobalt, chromium, and platinum. 

In a linear complex, the coordination number is 2, corresponding to one group on each side of the central atom. The silver-ammonia complex, which generally forms when a very slightly soluble silver salt such as silver chloride dissolves in aqueous ammonia, is an example, as shown in Figure 22-6. Another example of a linear com-... 

The majority of ligands are either neutral or anionic. Those which coordinate to a metal ion through a single atom are described as monodentate or unidentate. Examples of such ligands which we have encountered thus far include water, ammonia and chloride. A more extensive listing of common ligands is found in Table 1-3. We stress at this point that there is no difference in kind between the interactions of a metal centre with either neutral or anionic ligands. 

The most intriguing results were obtained for cobalt(III) chloride. By 1890, several ammonia compounds of C0CI3 had been isolated. These coordination compounds differed in several of their properties, the most striking of which were their beautiful colors. At the time, the formulas of these cobalt complexes were written as follows ... 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

In the complex [Co(NH3)6]Cl3, the cation is [Co(NH3)6]3+, and it is named first. The coordinated ammonia molecules are named as ammine, with the number of them being indicated by the prefix hexa. Therefore, the name for the compound is hexaamminecobalt(III) chloride. There are no spaces in the name of the cation. [Co(NH3)5C1]C12 has five NH3 molecules and one CN coordinated to Co3+. Following the rules just listed leads to the name pentaamminechlorocobalt(III) chloride. Potassium hexacyanoferrate(III) is K3[Fe(CN)6j. Reinecke s salt, NH4[Cr(NCS)4(NH3)2], would be named as ammonium diamminetetrathiocyanatochro mate (III). In Magnus s green salt, [Pt(NH3)4][PtCl4], both cation and anion are complexes. The name of the complex is tetraammineplatinum(II) tetrachloroplatinate(II). The compound [Co(en)3](N03)3 is named as tris(ethylenediamine)cobalt(III) nitrate. 

It seems safe to say that coordination will generally decrease the reactivity of donor atoms in the first row of the periodic table through steric effects. With some reactions the extent of this steric hindrance may be small. Ammonia can be transformed into chloramines when coordinated (34), and aromatic acid chlorides coordinated to A1C13 or TiCl4 may be esterified even when the functional group is a hindered one, as in mesitylene carbonyl chloride (47). These last reactions may proceed through a very reactive carbonium ion, whose existence is rendered possible by the polarization of the ligand which it suffers as a result of coordination. 

Weroer. in formulating his ideas about the structure of coordination compounds, had before hint facts such as the following. Four complexes of cobaltflll) chloride with ammonia had been discovered and named according to their colors ... 

From inis conclusion Wemcr postulated perhaps the most important part of his theory that in this series of compounds cobalt exhibits a constant coordination number of 6. and as ammonia molecules are removed, they are replaced by chloride ions which then act as though they are covalently bound to the cobalt rather than as free chloride ions. To describe the complex chemistry of cobalt, one must therefore consider not only the oxi tion state of the metal but also its coordination number. 

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