专业外语PPT5

Mn+ + x:L -----→ M(:L)xn+ The forward reaction is coordination and the reverse reaction is dissociation. Both coordination and dissociation usually occur in stepwise fashion when x is greater than l, so that the general equation above may be the sum of several stepwise equations.

Here both the anionic oxygen and the nonionic nitrogen have unshared electron pairs and may coordinate with a given cation. An example is the complex [Co (H2NCH2CO2 )3]. in which the cobalt is coordinated with the nitrogen and one of the oxygens of each glycinate. A polydentate ligand, when coordinated at two or more points to a central ion, forms a ring structure such as illustrated by the ethylenediamine complex of cobalt above3. This type of complex is called a chelate, and the polydentate ligand is a chelating group.
Ligands that are divalent or contain two donor atoms, like ethylenediamine (H2N— CH2—CH2 — NH2) . are bidentate because they contain two points or sites that enter into bonds with the central ion.
At the other extreme, complexes like Fe(CN)64- involve primarily covalent bonding. This variation in behavior is further illustrated by compounds listed in Table 9. The first four compounds listed are saltlike substances in which either the cation or anion is complex. This is apparent from1 their composition in aqueous solution. However, these same ions exist in the solids, although their formulas may be written as double salts as in the table.
In each of these cases the complex ion survives through the. Solution process and there is little evidence of free ligand or hydrated monatomic cation in solution. Note that the ligands may be molecular, as NH3, or anionic, as CN-. NO2- , or F. In the case of VF4(H2O)2-, vanadium is coordinated with both anionic and molecular ligands. The fifth compound, Pt2Cl4•4NH3, contains both complex cation and complex anion in solution and in the solid. The last compound has a crystal structure indicating the presence of CuCl42- complex ions.


The nature of the coordinate bond varies from essentially covalent, including double bond character in some cases, to essentially ionic. In the case of complexes such as Na(H2O)x + in aqueous solution, the sodium ion interacts with the coordinated water molecules much as a sodium ion in crystalline sodium chloride interacts with neighboring chloride ions. The bonding forces can be treated as electrostatic interactions.
Unit Five THE COORDINATION COMPLEX
一.词汇(WORDS)
1.ligand: n. 配体 ligand field crystal field 2.forward: adj. forward reaction reverse reaction 3.electrostatic: adj. 静电的 4.saltlike: adj. 类似盐的 5. polar: adj.极性的 polarizable: adj.可 极化的 6.unidentate: adj. 单齿的 unidentate ligand: bidentate: adj

7.ethylenediamine: n. 乙二胺 8.glycinate: n. 甘氨酸盐 9.chelate: n. 螯合物 10.cyano- chloro- carbonato- amineaquo- carbonyl- bitroso- acetatonitrato- hydroxo- oxalate 11.much as: 与~类似，象～一样。 12.enter into ：参加，成为～的一部分。

However, when the substance is dissolved in water, a mixture of hydrated monatomic ions results. This simply indicates that Cu ( II ) forms a more stable complex with water ligands than with chloride ligands, and that a high degree of ionic character allows rapid conversion to hydrated Cu( Ⅱ ) upon solution. The absence of CuCl42- in solution does not prove that it is not present in the solid.

二.课文（TEXTis for the formation of a coordination complex is the coordinate bond. There must be an electron-pair acceptor and an electron-pair donor. Thus, coordination reactions are examples of Lewis acid-base neutralization. The central ion is the Lewis acid, or electron-pair acceptor, and the surrounding groups, called ligands, are Lewis bases or electron-pair donors. In general, this reaction may be described as
The extent of the attractive forces determines the stability of the complex, and is dependent on the charge and size of the central ion and ligands.

Using this theory, it is possible to calculate the energy effects for many of the charge and size factors and finally to obtain values for bond energies. The latter are useful in predicting properties and types of configurations for a large number of compounds.
Ligand Groups Ligands must be polar or polarizable (nonpolar molecules are poor coordinating groups), and they usually have unshared electron pairs that may form coordinate bonds with the central ion. Ligands may be classified (Table 10.) on the basis of their ability to form one bond with the metal ion (unidentate) or their ability to form two bonds (bidentate).