化學專業(yè)英語之配位化合物

1、化學專業(yè)英語之配位化合物THE COORDINATION COMPLEXThe chemical basis for the formati on of a coordi nati on complex is the coordi nate bond. There must be an electro n-pair acceptor and an electro n-pair donor. Thus, coord in ati on reacti ons are examples of Lewis acid-base neutralization. The central ion is the

2、 Lewis acid, or electr on-pair acceptor, and the surro unding groups, called liga nds, are Lewis bases or electro n-pair donors. In gen eral, this react ion may be described asM+ + x:L - M(:L) xn+The forward reacti on is coordi nati on and the reverse react ion is dissociati on. Both coord in atio n

3、 and dissociati on usually occur in stepwise fashi on whe n x is greater tha n l, so that the gen eral equatio n above may be the sum of several stepwise equati ons.The n ature of the coord in ate bond varies from esse ntially covale nt, in clud ing double bond character in some cases, to esse ntial

4、ly ionic. In the case of complexes such as Na(H2O)x + in aqueous soluti on, the sodiumion in teracts with the coord in ated water molecules much as a sodium ion in crystalli ne sodium chloride in teractswith n eighbori ng chloride ions.The bonding forces can be treated as electrostatic in teract ion

5、s. At the other extreme, complexes like Fe(CN)64- i nvo Ive primarily covale nt bonding. This variationin behavior is further illustrated by compoundslistedinTable 9. The first four compoundslisted are saltlikesubstances in whicheither the cati on or anion is complex. This is appare nt from1 theirco

6、mposition in aqueous solution. However, these same ions exist in the solids, although their formulasmay be writte nas double salts as in thetable. In each of these cases the complex ion survives through the.Solution process and there is littleevidenee of free ligand or hydratedmon atomic eatio n in

7、soluti on.Note that the liga nds maybe molecular, asNH, or anionic, as CN -. NO2- , or F -. In the case of VF4(出0)2-, va nadiumis coordinated with both anionic and molecular ligands. The fifthcompound,Pt2Cl4?4NH, contains both complex cation and complex anion in solution and in the solid. The last c

8、ompo und has a crystal structure in dicat ing2the presenee of CuCl 4 complex ions.However, when the substanee is dissolved in water, a mixture of hydrated mon atomic ions results. This simply in dicates that Cu (II ) forms a more stable complex with water ligands than with chloride ligands, and that

9、 a high degree of ionic character allows rapid conversion to hydrated Cu( I ) upon solution. The absenee of CuCl42- in solution does not prove that itis not prese nt in the solid.Table 9. Examples of Coordnation ComplexesSolidSolution in WaterCoClrfiNH!CoCNHjjr ,cr(aq)4KCN-Ee(CN)K + (aq)tFe(CN)；-3KN

10、O)-Cu<NOa)aNH4F*VF»'2HONHt+(aq).VFHjOiEt<NHy)r >pTcir2KCl<ua3-2kk()K+<aq)(aq) #C1Liga nd field theory.A recent theory which has proven useful in connection with coordination compoundsis the crystal field or ligand field theory, which states that liga nds are held to the een t

11、ral ion of a coord in atio n compo und by electrostatic attractive forces due primarily to the charge of the eentral2ion and the polar n ature of the liga nds. The exte nt of the attractive forces determines the stability of the complex, and is dependent on the charge and size of the cen tral ion an

12、d liga nds.Using this theory, it is possible to calculate the energy effects formanyof the charge and size factors and fin allyto obtai n values for bonden ergies. The latter are useful in predict ing properties and types of con figurati ons for a large nu mber of compo un ds.Liga nd GroupsLiga nds

13、must be polar or polarizable (non polar molecules are poorcoordin at inggroups), and they usually have un shared electro n pairs thatmayform coord in ate bonds with the cen tral ion. Liga nds maybe classified (Table 10.) on the basis of their ability to form one bond with the metal ion (unidentate)o

14、r their ability to form two bonds (bidentate).Ligandsthat are divale nt or contain two donor atoms, like ethyle nediam ine(H2N CHCH NH2) . are bide ntate because they contain two poi nts or sites that en ter into bonds with the cen tral ion.Liga nds may be still more complex and many tride ntate, te

15、trade ntate,and even liexadentateligands are known. Polydentate ligands mayhave bothn eutral and anion ic sites that coord in ate with the cen tral ion, such as the glyci nate ion:Here both the anionic oxyge n and the nonionic n itroge n have un sharedelectro n pairs and maycoord in ate with a give

16、n cati on. Anexample is thecomplex Co (H 2NCI2CO) 3. in which the cobalt is coordinated with the nitrogen and one of the oxygens of each glycinate.A polydentate ligand,whe n coordi nated at two or more points to a cen tral ion, forms a ring structure such as illustrated by the ethyle nediam ine comp

17、lex of cobalt above . This type of complex is called a chelate, and the polydentate liga nd is a chelati ng group.Nam ing and Examples of Coordi nati on Compo unds1. Cati ons are n amed first, anions last.2. The namesof negative ion ligands end in o. Examples from Table 10. are cyano-, hydroxo-,chlo

18、ro-,carb on ato-. The order of liga nds isalphabetic.3. Neutral un its have historical endin gs, such as ammine, aqua-(formerly aquo-), carb on yl, n itroso-.4. The oxidation number of the central atom in the complex is specified by Romannumerals in parentheses following the nameof the element. When a complex ion is negative, the name of the central element has -ateappended.5. Neutral complexes are n amed as if they were cati on s'.6. If a complex is a positive ion, the n ames of the acid radicals notin the comp