Complex compounds

Lecture summary

Goals. To form ideas about the composition, structure, properties and nomenclature of complex compounds; develop skills in determining the degree of oxidation of a complexing agent, compiling equations for the dissociation of complex compounds.
New concepts: complex compound, complexing agent, ligand, coordination number, outer and inner spheres of the complex.
Equipment and reagents. Stand with test tubes, concentrated ammonia solution, solutions of copper(II) sulfate, silver nitrate, sodium hydroxide.

DURING THE CLASSES

Laboratory experience. Add ammonia solution to copper(II) sulfate solution. The liquid will turn an intense blue color.

What happened? Chemical reaction? Until now, we did not know that ammonia can react with salt. What substance was formed? What is its formula, structure, name? What class of compounds does it belong to? Can ammonia react with other salts? Are there connections similar to this? We have to answer these questions today.

To better study the properties of some compounds of iron, copper, silver, aluminum, we need knowledge of complex compounds.

Let's continue our experience. The resulting solution is divided into two parts. Let's add alkali to one part. Precipitation of copper (II) hydroxide Cu (OH) 2 is not observed, therefore, there are no doubly charged copper ions in the solution or there are too few of them. From this we can conclude that copper ions interact with the added ammonia and form some new ions that do not give an insoluble compound with OH - ions.

At the same time, the ions remain unchanged. This can be seen by adding a solution of barium chloride to the ammonia solution. A white precipitate of BaSO 4 will immediately fall out.

Studies have established that the dark blue color of the ammonia solution is due to the presence of complex 2+ ions in it, formed by attaching four ammonia molecules to the copper ion. When water evaporates, 2+ ions bind to ions, and dark blue crystals stand out from the solution, the composition of which is expressed by the formula SO 4 H 2 O.

Complex compounds are compounds that contain complex ions and molecules that can exist both in crystalline form and in solutions.

Formulas of molecules or ions of complex compounds are usually enclosed in square brackets. Complex compounds are obtained from conventional (non-complex) compounds.

Examples of obtaining complex compounds

The structure of complex compounds is considered on the basis of the coordination theory proposed in 1893 by the Swiss chemist Alfred Werner, Nobel Prize winner. His scientific activity took place at the University of Zurich. The scientist synthesized many new complex compounds, systematized previously known and newly obtained complex compounds and developed experimental methods for proving their structure.

A. Werner (1866–1919)

In accordance with this theory, complex compounds are distinguished complexing agent, external and inner sphere. The complexing agent is usually a cation or a neutral atom. The inner sphere is made up of a certain number of ions or neutral molecules that are firmly bound to the complexing agent. They are called ligands. The number of ligands determines coordination number(KN) complexing agent.

An example of a complex compound

Considered in the example, the compound SO 4 H 2 O or CuSO 4 5H 2 O is a crystalline hydrate of copper (II) sulfate.

Let's define the constituent parts of other complex compounds, for example K 4 .
(Reference. The substance with the formula HCN is hydrocyanic acid. Hydrocyanic acid salts are called cyanides.)

The complexing agent is an iron ion Fe 2+, the ligands are cyanide ions CN - , the coordination number is six. Everything written in square brackets is the inner sphere. Potassium ions form the outer sphere of the complex compound.

The nature of the bond between the central ion (atom) and ligands can be twofold. On the one hand, the connection is due to the forces of electrostatic attraction. On the other hand, between the central atom and ligands a bond can be formed by the donor-acceptor mechanism by analogy with the ammonium ion. In many complex compounds, the bond between the central ion (atom) and the ligands is due both to the forces of electrostatic attraction and to the bond formed due to the unshared electron pairs of the complexing agent and free orbitals of the ligands.

Complex compounds having an outer sphere are strong electrolytes and in aqueous solutions dissociate almost completely into a complex ion and ions outer sphere. For example:

SO 4 2+ + .

In exchange reactions, complex ions pass from one compound to another without changing their composition:

SO 4 + BaCl 2 \u003d Cl 2 + BaSO 4.

The inner sphere can have a positive, negative, or zero charge.

If the charge of the ligands compensates for the charge of the complexing agent, then such complex compounds are called neutral or nonelectrolyte complexes: they consist only of the complexing agent and ligands of the inner sphere.

Such a neutral complex is, for example, .

The most typical complexing agents are cations d-elements.

Ligands can be:

a) polar molecules - NH 3, H 2 O, CO, NO;
b) simple ions - F - , Cl - , Br - , I - , H - , H + ;
c) complex ions - CN -, SCN -, NO 2 -, OH -.

Let's consider a table that shows the coordination numbers of some complexing agents.

Nomenclature of complex compounds. In a compound, the anion is named first, and then the cation. When specifying the composition of the inner sphere, first of all, anions are called, adding to the Latin name the suffix - about-, for example: Cl - - chloro, CN - - cyano, OH - - hydroxo, etc. Hereafter referred to as neutral ligands and primarily ammonia and its derivatives. In this case, the following terms are used: for coordinated ammonia - ammine, for water - aqua. The number of ligands is indicated in Greek words: 1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa. Then they move on to the name of the central atom. If the central atom is part of the cations, then the Russian name of the corresponding element is used and its oxidation state is indicated in brackets (in Roman numerals). If the central atom is contained in the anion, then use the Latin name of the element, and at the end add the ending - at. In the case of non-electrolytes, the oxidation state of the central atom is not given, because it is uniquely determined from the condition of electroneutrality of the complex.

Examples. To name the Cl 2 complex, the oxidation state is determined (S.O.)
X complexing agent - Cu ion X+ :

1 x + 2 (–1) = 0,x = +2, C.O.(Cu) = +2.

Similarly, the oxidation state of the cobalt ion is found:

y + 2 (–1) + (–1) = 0,y = +3, S.O.(Co) = +3.

What is the coordination number of cobalt in this compound? How many molecules and ions surround the central ion? The coordination number of cobalt is six.

The name of the complex ion is written in one word. The oxidation state of the central atom is indicated by a Roman numeral placed in parentheses. For example:

Cl 2 - tetraammine copper (II) chloride,
NO 3 – dichloroaquatriamminecobalt(III) nitrate,
K 3 - hexacyanoferrate(III) potassium,
K 2 - tetrachloroplatinate (II) potassium,
- dichlorotetraamminzinc,
H 2 - hexachlorotinic acid.

On the example of several complex compounds, we will determine the structure of molecules (ion-complexing agent, its S.O., coordination number, ligands, inner and outer spheres), give the name of the complex, write down the equations of electrolytic dissociation.

K 4 - potassium hexacyanoferrate (II),

K 4 4K + + 4– .

H - tetrachloroauric acid (formed by dissolving gold in aqua regia),

H H + + –.

OH - diammine silver (I) hydroxide (this substance is involved in the "silver mirror" reaction),

OH + + OH - .

Na - tetrahydroxoaluminate sodium,

Na Na + + - .

Many organic substances also belong to complex compounds, in particular, the products of the interaction of amines with water and acids known to you. For example, salts of methyl ammonium chloride and phenylammonium chloride are complex compounds. According to the coordination theory, they have the following structure:

Here, the nitrogen atom is a complexing agent, the hydrogen atoms at nitrogen, and the methyl and phenyl radicals are ligands. Together they form the inner sphere. In the outer sphere are chloride ions.

Many organic substances that are of great importance in the life of organisms are complex compounds. These include hemoglobin, chlorophyll, enzymes and others

Complex compounds are widely used:

1) in analytical chemistry for the determination of many ions;
2) for the separation of certain metals and the production of high purity metals;
3) as dyes;
4) to eliminate water hardness;
5) as catalysts for important biochemical processes.

Chemistry test - complex compounds - URGENT! and got the best answer

Answer from Nick[guru]
Some questions are set incorrectly, for example 7,12,27. Therefore, the answers contain reservations.
1. What is the coordination number of the complexing agent in the +2 complex ion?
AT 6
2. What is the coordination number of the complexing agent in the 2+ complex ion?
B) 6
3. What is the coordination number of the complexing agent in the complex ion 2+
B) 4
4. What is the coordination number of Сu²+ in the + complex ion?
B) 4
5. What is the coordination number of the complexing agent in the complex ion: +4?
B) 6
6. Determine the charge of the central ion in the complex compound K4
B) +2
7. What is the charge of a complex ion?
B) +2 - if we assume that the complexing agent is Сu (II)
8. Among the iron salts, determine the complex salt:
A) K3
9. What is the coordination number of Pt4+ in the 2+ complex ion?
A) 4
10. Determine the charge of the complex ion K2?
B) +2
11. Which molecule corresponds to the name tetraammine copper (II) dichloride?
B) Cl2
12. What is the charge of a complex ion?
D) +3 - if we assume that the complexing agent is Cr (III)
13. Among the salts of copper (II), determine the complex salt:
B) K2
14. What is the coordination number of Co3+ in the complex ion +?
B) 6
15. Determine the charge of the complexing agent in the complex compound K3?
D) +3
16. Which molecule corresponds to the name potassium tetraiodohydrate (II)?
A) K2
17. What is the charge of a complex ion?
IN 2
18. Among nickel (II) salts, determine the complex salt:
B) SO4
19. What is the coordination number of Fe3+ in the -3 complex ion?
AT 6
20. Determine the charge of the complexing agent in the complex compound K3?
B) +3
21. Which molecule corresponds to the name silver(I) diamine chloride?
B) Cl
22. What is the charge of the K4 complex ion?
B) -4
23. Among the zinc salts, determine the complex salt
B) Na2
24. What is the coordination number of Pd4+ in the 4+ complex ion?
D) 6
25. Determine the charge of the complexing agent in the complex compound H2?
B) +2
26. Which molecule corresponds to the name potassium hexacyanoferrate (II)?
D) K4
27. What is the charge of a complex ion?
D) -2 - if we assume that the complexing agent is Co (II)
27. Among the compounds of chromium (III), determine the complex compound
C) [Cr (H2O) 2(NH3)4]Cl3
28. What is the coordination number of cobalt (III) in the NO3 complex ion?
B) 6
29. Determine the charge of the complexing agent in the complex compound Cl2
A) +3
30. Which molecule corresponds to the name sodium tetraiodopalladate (II)?
D) Na2

Answer from James Bond[newbie]
Oh my God

Answer from Kitten...[guru]
#30 latest

The nomenclature of complex compounds is an integral part of the nomenclature of inorganic substances. The rules for naming complex compounds are systematic (unambiguous). In accordance with the recommendations of IUPAC, these rules are universal, since, if necessary, they can also be applied to simple inorganic compounds, if there are no traditional and special names for the latter. Names built according to systematic rules are adequate to chemical formulas. The formula of a complex compound is compiled according to the general rules: first the cation is written - complex or ordinary, then the anion - complex or ordinary. In the inner sphere of a complex compound, the central complexing atom is first written, then uncharged ligands (molecules), then negatively charged anion ligands.

Single-core complexes

In the names of cationic, neutral, and most anionic complexes, the central atoms have the Russian names of the corresponding elements. In some cases, for anionic complexes, the roots of the Latin names of the elements of the central complexing atom are used. For example, - dichlorodiammineplatinum, 2- - tetrachloroplatinate (II) -ion, + - diamminesilver (I) cation, - - dicyanoargenate (I) -ion.

The name of a complex ion begins with an indication of the composition of the inner sphere. First of all, the anions located in the inner sphere are listed in alphabetical order, adding the ending “o” to their Latin name. For example, OH - - hydroxo, Cl - - chloro, CN - - cyano, CH 3 COO - - acetate, CO 3 2- - carbonate, C 2 O 4 2- - oxalato, NCS - - thiocyanato, NO 2 - - nitro , O 2 2- - oxo, S 2- - thio, SO 3 2- - sulfito, SO 3 S 2- - thiosulfato, C 5 H 5 - cyclopentadienyl, etc. Then the intrasphere neutral molecules are indicated in alphabetical order. For neutral ligands, one-word names of substances are used without changes, for example, N 2 -diazot, N 2 H 4 -hydrazine, C 2 H 4 - ethylene. Intrasphere NH 3 is called ammino-, H 2 O - aqua, CO-carbonyl, NO-nitrosyl. The number of ligands is indicated by Greek numerals: di, three, tetra, penta, hexa, etc. If the names of the ligands are more complex, for example, ethylenediamine, they are preceded by the prefixes "bis", "tris", "tetrakis", etc.

The names of complex compounds with an outer sphere consist of two words (generally "cation anion"). The name of the complex anion ends with the suffix -at. The oxidation state of the complexing agent is indicated by Roman numerals in brackets after the name of the anion. For example:

K 2 - potassium tetrachloroplatinate (II),

Na 3 [Fe (NH 3) (CN) 5] - sodium pentacyanomonoammine ferrate (II),

H 3 O - oxonium tetrachloroaurate (III),

K is potassium diiodoiodate(I),

Na 2 - sodium hexahydroxostannate (IV).

In compounds with a complex cation, the oxidation state of the complexing agent is indicated after its name in Roman numerals in brackets. For example:

Cl is diammine silver (I) chloride,

Br is trichlorotriammineplatinum(IV) bromide,

NO 3 -

Chloronitrotetraamminecobalt(III) nitrate.

The names of complex compounds - non-electrolytes without an external sphere consist of one word, the oxidation state of the complexing agent is not indicated. For example:

- trifluorothriaquocobalt,

- tetrachlorodiammine platinum,

- bis (cyclopentadienyl) iron.

The name of compounds with complex cation and anion is composed of the names of the cation and anion, for example:

hexanitrocobaltate(III) hexaamminecobalt(III),

trichloroammineplatinate (II) platinum(II)chlorotriammine.

For complexes with ambidentate ligands, the name indicates the symbol of the atom with which this ligand is bonded to the central complexing atom:

2- - tetrakis (ticyanato-N) cobaltate (II) -ion,

2- - tetrakis(thiocyanato-S) mercurate(II) - ion.

Traditionally, the ambidentate ligand NO 2 - is called a nitro ligand if the donor atom is nitrogen, and a nitrito ligand if the donor atom is oxygen (–ONO -):

3- - hexanitrocobaltate (III) -ion,

3- - hexanitritocobaltate (III) -ion.

Classification of complex compounds

Complex ions can be part of the molecules of various classes of chemical compounds: acids, bases, salts, etc. Depending on the charge of the complex ion, cationic, anionic and neutral complexes.

Cation complexes

In cationic complexes, the central complexing atom is cations or positively polarized atoms of the complexing agent, and the ligands are neutral molecules, most often water and ammonia. Complex compounds in which water acts as a ligand are called aquacomplexes. These compounds include crystalline hydrates. For example: MgCl 2 × 6H 2 O

or Cl2,

CuSO 4 × 5H 2 O or ∙SO 4 ∙ H 2 O, FeSO 4 × 7H 2 O or SO 4 × H 2 O

In the crystalline state, some aqua complexes (for example, copper sulphate) also retain water of crystallization, which is not part of the inner sphere, which is less firmly bound and easily split off when heated.

One of the most numerous classes of complex compounds is amino complexes (ammonates) and aminates. The ligands in these complexes are ammonia or amine molecules. For example: SO 4, Cl 4,

Cl2.

Anion complexes

Ligands in such compounds are anions or negatively polarized atoms and their groups.

Anionic complexes include:

a) complex acids H, H 2, H.

b) double and complex salts of PtCl 4 × 2KCl or K 2,

HgI 2 × 2KI or K 2 .

c) oxygen-containing acids and their salts H 2 SO 4 , K 2 SO 4 , H 5 IO 6 , K 2 CrO 4 .

d) hydroxosalts K, Na 2 .

e) polyhalides: K, Cs.

Neutral complexes

Such compounds include complex compounds that do not have an outer sphere and do not give complex ions in aqueous solutions: , , carbonyl complexes , .

Cation-anion complexes

The compounds simultaneously contain both a complex cation and a complex anion:

, .

Cyclic complexes (chelates)

Coordination compounds in which the central atom (or ion) is simultaneously bonded to two or more donor atoms of the ligand, as a result of which one or more heterocycles are closed, are called chelates . Ligands that form chelate rings are called chelating (chelating) reagents. The closure of the chelate ring by such ligands is called chelation(chelation). The most extensive and important class of chelates are metal chelate complexes. The ability to coordinate ligands is inherent in metals of all oxidation states. For elements of the main subgroups, the central complexing atom is usually in the highest oxidation state.

Chelating reagents contain two main types of electron donor centers: a) groups containing a mobile proton, for example, -COOH, -OH, -SO 3 H; when they are coordinated to the central ion, proton substitution and b) neutral electron-donor groups, for example, R 2 CO, R 3 N, are possible. Bidentate ligands occupy two places in the inner coordination sphere of the chelate, such as, for example, ethylenediamine (Fig. 3).

According to Chugaev's cycle rule, the most stable chelate complexes are formed when the cycle contains five or six atoms. For example, among diamines of composition H 2 N-(CH 2)n-NH 2 the most stable complexes are formed for n=2 (five-membered cycle) and n=3 (six-membered cycle).

Fig.3. Copper(II) bisethylenediamine cation.

Chelates in which, at the closing of the chelate cycle, the ligand uses a proton-containing and neutral electron-donor groups and is formally bound to the central atom by a covalent and donor-acceptor bond, called are intracomplex compounds. Thus, polydentate ligands with acidic functional groups can form chelate compounds. Intercomplex compounds are a chelate in which ring closure is accompanied by the displacement of one or more protons from acidic functional groups by a metal ion, in particular, copper(II) glycinate is an intracomplex compound:

Fig.4. Intercomplex compound of 8-hydroxyquinoline with zinc.

Hemoglobin and chlorophyll are also intracomplex compounds.

The most important feature of chelates is their increased stability compared to similarly constructed noncyclic complexes.

Chapter 17

17.1. Basic definitions

In this chapter, you will be introduced to a special group of complex substances called comprehensive(or coordinating) compounds.

Currently, a strict definition of the concept " complex particle" no. The following definition is usually used.

For example, a hydrated copper ion 2 is a complex particle, since it actually exists in solutions and some crystalline hydrates, it is formed from Cu 2 ions and H 2 O molecules, water molecules are real molecules, and Cu 2 ions exist in crystals of many copper compounds. On the contrary, the SO 4 2 ion is not a complex particle, since although O 2 ions occur in crystals, the S 6 ion does not exist in chemical systems.

Examples of other complex particles: 2 , 3 , , 2 .

At the same time, NH 4 and H 3 O ions are classified as complex particles, although H ions do not exist in chemical systems.

Sometimes complex particles are called complex chemical particles, all or part of the bonds in which are formed according to the donor-acceptor mechanism. This is true in most complex particles, but, for example, in potassium alum SO 4 in complex particle 3, the bond between Al and O atoms is indeed formed according to the donor-acceptor mechanism, while in the complex particle there is only electrostatic (ion-dipole) interaction. This is confirmed by the existence in iron ammonium alum of a complex particle similar in structure, in which only ion-dipole interaction is possible between water molecules and the NH 4 ion.

By charge, complex particles can be cations, anions, and also neutral molecules. Complex compounds containing such particles can belong to different classes of chemicals (acids, bases, salts). Examples: (H 3 O) - acid, OH - base, NH 4 Cl and K 3 - salts.

Typically, the complexing agent is an atom of an element that forms a metal, but it can also be an atom of oxygen, nitrogen, sulfur, iodine, and other elements that form non-metals. The oxidation state of the complexing agent may be positive, negative, or zero; when a complex compound is formed from simpler substances, it does not change.

Ligands can be particles that, before the formation of a complex compound, were molecules (H 2 O, CO, NH 3, etc.), anions (OH, Cl, PO 4 3, etc.), as well as a hydrogen cation. Distinguish unidentate or monodentate ligands (linked to the central atom through one of its atoms, that is, by one -bond), bidentate(connected to the central atom through two of their atoms, that is, by two -bonds), tridentate etc.

If the ligands are unidentate, then the coordination number is equal to the number of such ligands.

The cn depends on the electronic structure of the central atom, its degree of oxidation, the size of the central atom and ligands, the conditions for the formation of the complex compound, temperature, and other factors. CN can take values ​​from 2 to 12. Most often it is equal to six, somewhat less often - four.

There are also complex particles with several central atoms.

Two types of structural formulas of complex particles are used: indicating the formal charge of the central atom and ligands, or indicating the formal charge of the entire complex particle. Examples:

To characterize the shape of a complex particle, the idea of ​​a coordination polyhedron (polyhedron) is used.

Coordination polyhedra also include a square (KN = 4), a triangle (KN = 3), and a dumbbell (KN = 2), although these figures are not polyhedra. Examples of coordination polyhedra and correspondingly shaped complex particles for the most common CN values ​​are shown in Figs. one.

17.2. Classification of complex compounds

How chemicals complex compounds are divided into ionic (they are sometimes called ionogenic) and molecular ( non-ionic) connections. Ionic complex compounds contain charged complex particles - ions - and are acids, bases or salts (see § 1). Molecular complex compounds consist of uncharged complex particles (molecules), for example: or - it is difficult to assign them to any main class of chemicals.

The complex particles that make up complex compounds are quite diverse. Therefore, several classification features are used for their classification: the number of central atoms, the type of ligand, the coordination number, and others.

According to the number of central atoms complex particles are divided into single-core and multi-core. The central atoms of multinuclear complex particles can be linked to each other either directly or through ligands. In both cases, the central atoms with ligands form a single inner sphere of the complex compound:

According to the type of ligands, complex particles are divided into

1) Aquacomplexes, that is, complex particles in which water molecules are present as ligands. Cationic aquacomplexes m are more or less stable, anionic aquacomplexes are unstable. All crystalline hydrates are compounds containing aqua complexes, for example:

Mg(ClO 4) 2. 6H 2 O is actually (ClO 4) 2 ;
BeSO4. 4H 2 O is actually SO 4 ;
Zn(BrO 3) 2 . 6H 2 O is actually (BrO 3) 2 ;
CuSO4. 5H 2 O is actually SO 4 . H2O.

2) Hydroxocomplexes, that is, complex particles in which hydroxyl groups are present as ligands, which were hydroxide ions before entering the complex particle, for example: 2 , 3 , .

Hydroxo complexes are formed from aqua complexes that exhibit the properties of cationic acids:

2 + 4OH = 2 + 4H 2 O

3) Ammonia, that is, complex particles in which NH 3 groups are present as ligands (before the formation of a complex particle - ammonia molecules), for example: 2 , , 3 .

Ammonia can also be obtained from aqua complexes, for example:

2 + 4NH 3 \u003d 2 + 4 H 2 O

The color of the solution in this case changes from blue to ultramarine.

4) acidocomplexes, that is, complex particles in which acid residues of both oxygen-free and oxygen-containing acids are present as ligands (before the formation of a complex particle - anions, for example: Cl, Br, I, CN, S 2, NO 2, S 2 O 3 2 , CO 3 2 , C 2 O 4 2 etc.).

Examples of the formation of acid complexes:

Hg 2 + 4I = 2
AgBr + 2S 2 O 3 2 = 3 + Br

The latter reaction is used in photography to remove unreacted silver bromide from photographic materials.
(When developing photographic film and photographic paper, the unexposed part of the silver bromide contained in the photographic emulsion is not restored by the developer. To remove it, this reaction is used (the process is called "fixing", since the unremoved silver bromide gradually decomposes in the light, destroying the image)

5) Complexes in which hydrogen atoms are ligands are divided into two completely different groups: hydride complexes and complexes included in the composition onium connections.

In the formation of hydride complexes - , , - the central atom is an electron acceptor, and the hydride ion is a donor. The oxidation state of hydrogen atoms in these complexes is –1.

In onium complexes, the central atom is an electron donor, and the acceptor is a hydrogen atom in the +1 oxidation state. Examples: H 3 O or - oxonium ion, NH 4 or - ammonium ion. In addition, there are substituted derivatives of such ions: - tetramethylammonium ion, - tetraphenylarsonium ion, - diethyloxonium ion, etc.

6) Carbonyl complexes - complexes in which CO groups are present as ligands (before complex formation - carbon monoxide molecules), for example:,, etc.

7) Anion halide complexes are complexes of type .

Other classes of complex particles are also distinguished according to the type of ligands. In addition, there are complex particles with ligands of various types; the simplest example is aqua hydroxocomplex.

17.3. Fundamentals of the nomenclature of complex compounds

The formula of a complex compound is compiled in the same way as the formula of any ionic substance: the formula of the cation is written in the first place, and the anion in the second.

The formula of a complex particle is written in square brackets in the following sequence: the symbol of the complexing element is placed first, then the formulas of the ligands that were cations before the formation of the complex, then the formulas of the ligands that were neutral molecules before the formation of the complex, and after them the formulas of the ligands, former before the formation of the complex by anions.

The name of a complex compound is built in the same way as the name of any salt or base (complex acids are called hydrogen or oxonium salts). The name of the compound includes the name of the cation and the name of the anion.

The name of the complex particle includes the name of the complexing agent and the names of the ligands (the name is written in accordance with the formula, but from right to left. For complexing agents in cations, Russian element names are used, and in anions, Latin ones.

Names of the most common ligands:

H 2 O - aqua	Cl - chloro	SO 4 2 - sulfate	OH - hydroxo
CO - carbonyl	Br - bromo	CO 3 2 - carbonate	H - hydrido
NH 3 - ammine	NO 2 - nitro	CN - cyano	NO - nitroso
NO - nitrosyl	O 2 - oxo	NCS - thiocyanato	H + I - hydro

Examples of names of complex cations:

Examples of names of complex anions:

2 - tetrahydroxozincate ion
3 – di(thiosulfato)argentate(I)-ion
3 – hexacyanochromate(III)-ion
– tetrahydroxodiquaaluminate ion
– tetranitrodiamminecobaltate(III)-ion
3 – pentacyanoaquaferrate(II)-ion

Examples of the names of neutral complex particles:

More detailed nomenclature rules are given in reference books and special manuals.

17.4. Chemical bond in complex compounds and their structure

In crystalline complex compounds with charged complexes, the bond between the complex and the outer sphere ions is ionic, while the bonds between the remaining particles of the outer sphere are intermolecular (including hydrogen bonds). In molecular complex compounds, the bond between the complexes is intermolecular.

In most complex particles, the bonds between the central atom and the ligands are covalent. All or part of them are formed according to the donor-acceptor mechanism (as a result, with a change in formal charges). In the least stable complexes (for example, in the aqua complexes of alkaline and alkaline earth elements, as well as ammonium), ligands are held by electrostatic attraction. The bond in complex particles is often referred to as a donor-acceptor or coordination bond.

Let us consider its formation using the iron(II) aquacation as an example. This ion is formed by the reaction:

FeCl 2cr + 6H 2 O = 2 + 2Cl

The electronic formula of the iron atom is 1 s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6. Let's make a scheme of valence sublevels of this atom:

When a doubly charged ion is formed, the iron atom loses two 4 s-electron:

The iron ion accepts six electron pairs of oxygen atoms of six water molecules into free valence orbitals:

A complex cation is formed, the chemical structure of which can be expressed by one of the following formulas:

The spatial structure of this particle is expressed by one of the spatial formulas:

The shape of the coordination polyhedron is an octahedron. All Fe-O bonds are the same. Supposed sp 3 d 2 - hybridization of iron atom AO. The magnetic properties of the complex indicate the presence of unpaired electrons.

If FeCl 2 is dissolved in a solution containing cyanide ions, then the reaction proceeds

FeCl 2cr + 6CN = 4 + 2Cl.

The same complex is also obtained by adding a solution of potassium cyanide KCN to a FeCl 2 solution:

2 + 6CN \u003d 4 + 6H 2 O.

This suggests that the cyanide complex is stronger than the aquacomplex. In addition, the magnetic properties of the cyanide complex indicate the absence of unpaired electrons from the iron atom. All this is due to a slightly different electronic structure of this complex:

The "stronger" CN ligands form stronger bonds with the iron atom, the energy gain is enough to "break" the Hund's rule and release 3 d-orbitals for lone pairs of ligands. The spatial structure of the cyanide complex is the same as that of the aquacomplex, but the type of hybridization is different - d 2 sp 3 .

The "strength" of the ligand depends primarily on the electron density of the cloud of the lone pair of electrons, that is, it increases with a decrease in the size of the atom, with a decrease in the principal quantum number, depends on the type of EO hybridization and on some other factors. The most important ligands can be lined up in order of increasing their "strength" (a kind of "activity series" of ligands), this series is called spectrochemical series of ligands:

I; Br; : SCN, Cl, F, OH, H 2 O; : NCS, NH3; SO 3 S : 2 ; : CN, CO

For complexes 3 and 3, the formation schemes look as follows:

For complexes with CN = 4, two structures are possible: a tetrahedron (in the case sp 3-hybridization), for example, 2 , and a flat square (in the case of dsp 2 hybridization), for example, 2 .

17.5. Chemical properties of complex compounds

For complex compounds, first of all, the same properties are characteristic as for ordinary compounds of the same classes (salts, acids, bases).

If the compound is an acid, then it is a strong acid; if it is a base, then the base is strong. These properties of complex compounds are determined only by the presence of H 3 O or OH ions. In addition, complex acids, bases and salts enter into the usual exchange reactions, for example:

SO 4 + BaCl 2 \u003d BaSO 4 + Cl 2
FeCl 3 + K 4 = Fe 4 3 + 3KCl

The last of these reactions is used as a qualitative reaction for Fe 3 ions. The resulting ultramarine insoluble substance is called "prussian blue" [the systematic name is iron(III)-potassium hexacyanoferrate(II)].

In addition, the complex particle itself can enter into the reaction, and the more actively, the less stable it is. Usually these are ligand substitution reactions occurring in solution, for example:

2 + 4NH 3 \u003d 2 + 4H 2 O,

as well as acid-base reactions such as

2 + 2H 3 O = + 2H 2 O
2 + 2OH = + 2H 2 O

Formed in these reactions, after isolation and drying, it turns into zinc hydroxide:

Zn(OH) 2 + 2H 2 O

The last reaction is the simplest example of the decomposition of a complex compound. In this case, it runs at room temperature. Other complex compounds decompose when heated, for example:

SO4. H 2 O \u003d CuSO 4 + 4NH 3 + H 2 O (above 300 o C)
4K 3 \u003d 12KNO 2 + 4CoO + 4NO + 8NO 2 (above 200 o C)
K 2 \u003d K 2 ZnO 2 + 2H 2 O (above 100 o C)

To assess the possibility of a ligand substitution reaction, one can use the spectrochemical series, guided by the fact that stronger ligands displace weaker ones from the inner sphere.

17.6. Isomerism of complex compounds

Isomerism of complex compounds is related
1) with possible different arrangement of ligands and outer-sphere particles,
2) with a different structure of the most complex particle.

The first group includes hydrated(in general solvate) and ionization isomerism, to the second - spatial and optical.

Hydrate isomerism is associated with the possibility of different distribution of water molecules in the outer and inner spheres of the complex compound, for example: (red-brown color) and Br 2 (blue color).

Ionization isomerism is associated with the possibility of different distribution of ions in the outer and inner spheres, for example: SO 4 (purple) and Br (red). The first of these compounds forms a precipitate, reacting with a solution of barium chloride, and the second - with a solution of silver nitrate.

Spatial (geometric) isomerism, otherwise called cis-trans isomerism, is characteristic of square and octahedral complexes (it is impossible for tetrahedral ones). Example: cis-trans square complex isomerism

Optical (mirror) isomerism essentially does not differ from optical isomerism in organic chemistry and is characteristic of tetrahedral and octahedral complexes (impossible for square ones).

All inorganic compounds are divided into two groups:

1. first-order connections, i.e. compounds obeying the theory of valency;

2. connections of a higher order, i.e. compounds that do not obey the concepts of valency theory. Higher-order compounds include hydrates, ammoniates, etc.

CoCl 3 + 6 NH 3 \u003d Co (NH 3) 6 Cl 3

Werner (Switzerland) introduced into chemistry ideas about compounds of a higher order and gave them the name complex compounds. He referred to the CS all the most stable compounds of a higher order, which in an aqueous solution either do not decompose into constituent parts at all, or decompose to a small extent. In 1893, Werner suggested that any element, after saturation, can also exhibit an additional valence - coordinating. According to Werner's coordination theory, in each CS there are:

Cl3: complexing agent (KO \u003d Co), ligands (NH 3), coordination number (CN \u003d 6), inner sphere, external environment (Cl 3), coordination capacity.

The central atom of the inner sphere around which ions or molecules are grouped is called complexing agent. The role of complexing agents is most often performed by metal ions, less often by neutral atoms or anions. Ions or molecules coordinating around a central atom in the inner sphere are called ligands. Anions can be ligands: G -, OH-, SN-, CNS-, NO 2 -, CO 3 2-, C 2 O 4 2-, neutral molecules: H 2 O, CO, G 2, NH 3, N 2 H4. coordination number is the number of places in the inner sphere of the complex that can be occupied by ligands. CN is usually higher than the oxidation state. CN = 1, 2, 3, 4, 5, 6, 7, 8, 9, 12. The most common CN = 4, 6, 2. These numbers correspond to the most symmetrical configuration of the complex - octahedral (6), tetrahedral (4) and linear (2). KCh envy on the nature of the complexing agent and ligands, as well as on the sizes of CO and ligands. Coordination capacity of ligands is the number of places in the inner sphere of the complex occupied by each ligand. For most ligands, the coordination capacity is unity ( monodentate ligands), less than two ( bidentate ligands), there are ligands with a higher capacity (3, 4, 6) - polydentate ligands. The charge of the complex must be numerically equal to the total outer sphere and opposite in sign to it. 3+ Cl 3 -.

Nomenclature of complex compounds. Many complex compounds have retained their historical names associated with the color or the name of the scientist who synthesized them. The IUPAC nomenclature is currently used.

Ion listing order. The anion is called first, then the cation, while the root of the Latin name KO is used in the name of the anion, and its Russian name in the genitive case is used in the name of the cation.

Cl is diamminesilver chloride; K 2 - potassium trichlorocuprate.

Order of listing ligands. Ligands in the complex are listed in the following order: anionic, neutral, cationic - without separation by a hyphen. Anions are listed in the order H - , O 2- , OH - , simple anions, complex anions, polyatomic anions, organic anions.

SO 4 - chloronitrsulfate (+4)

End of coordination groups. Neutral groups are named the same as molecules. The exceptions are aqua (H 2 O), amine (NH 3). The vowel "O" is added to negatively charged anions.

– hexocyanoferrate (+3) hexaaminacobalt (+3)

Prefixes indicating the number of ligands.

1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa, 7 - hepta, 8 - octa, 9 - nona, 10 - deca, 11 - indeca, 12 - dodeca, many - poly.

The prefixes bis-, tris- are used before ligands with complex names, where there are already mono-, di-, etc. prefixes.

Cl 3 - tris (ethylenediamine) iron chloride (+3)

The names of complex compounds first indicate the anionic part in the nominative case and with the suffix -at, and then the cationic part in the genitive case. However, before the name of the central atom in both the anionic and cationic parts of the compound, all ligands coordinated around it are listed, indicating their number in Greek numerals (1 - mono (usually omitted), 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa, 7 - hepta, 8 - octa). The suffix -o is added to the names of the ligands, and anions are first called, and then neutral molecules: Cl- - chloro, CN- - cyano, OH- - hydroxo, C2O42- - oxalato, S2O32- - thiosulfato, (CH3) 2NH - dimethylamino and etc. Exceptions: the names of H2O and NH3 as ligands are as follows: "aqua" and "ammine". If the central atom is part of the cation, then the Russian name of the element is used, after which its oxidation state is indicated in brackets in Roman numerals. For the central atom in the composition of the anion, the Latin name of the element is used and the oxidation state is indicated before this name. For elements with a constant oxidation state, it can be omitted. In the case of non-electrolytes, the oxidation state of the central atom is also not indicated, since it is determined based on the electrical neutrality of the complex. Title examples:

Cl2 - dichloro-tetrammine-platinum(IV) chloride,

OH - diammine-silver(I) hydroxide.

Classification of complex compounds. Several different classifications of COPs are used.

1. by belonging to a certain class of compounds:

complex acids - H 2

complex bases -

complex salts - K 2

2. By the nature of ligands: aqua complexes, ammonia. Cyanide, halide, etc.

Aquacomplexes - complexes in which water molecules serve as ligands, for example Cl 2 - hexaaquacalcium chloride. Ammineates and aminates are complexes in which the ligands are molecules of ammonia and organic amines, for example: SO 4 - tetrammine copper (II) sulfate. Hydroxocomplexes. In them, OH- ions serve as ligands. Especially characteristic of amphoteric metals. Example: Na 2 - sodium tetrahydroxozincate (II). Acid complexes. In these complexes, the ligands are anions-acidic residues, for example, K 4 - potassium hexacyanoferrate(II).

3. by the sign of the charge of the complex: cationic, anionic, neutral

4. according to the internal structure of the CS: according to the number of nuclei that make up the complex:

mononuclear - H 2, binuclear - Cl 5, etc.,

5. by the absence or presence of cycles: simple and cyclic CSs.

Cyclic or chelate (pincer) complexes. They contain a bi- or polydentate ligand, which, as it were, captures the central atom M like cancer claws: Examples: Na 3 - sodium trioxalato-(III) ferrate, (NO 3) 4 - triethylenediamino-platinum (IV) nitrate.

The group of chelate complexes also includes intra-complex compounds in which the central atom is part of the cycle, forming bonds with ligands in various ways: by exchange and donor-acceptor mechanisms. Such complexes are very characteristic of aminocarboxylic acids, for example, glycine forms chelates with Cu 2+, Pt 2+ ions:

Chelate compounds are particularly strong, since the central atom in them is, as it were, blocked by a cyclic ligand. Chelates with five- and six-membered rings are the most stable. Complexons bind metal cations so strongly that when they are added, such poorly soluble substances as CaSO 4 , BaSO 4 , CaC 2 O 4 , CaCO 3 dissolve. Therefore, they are used to soften water, to bind metal ions during dyeing, processing photographic materials, and in analytical chemistry. Many chelate-type complexes have a specific color and, therefore, the corresponding ligand compounds are very sensitive reagents for transition metal cations. For example, dimethylglyoxime [C(CH 3)NOH] 2 serves as an excellent reagent for Ni2+, Pd2+, Pt2+, Fe2+, etc. cations.

Stability of complex compounds. Instability constant. When the CS is dissolved in water, decomposition occurs, and the inner sphere behaves as a single whole.

K = K + + -

Along with this process, the dissociation of the inner sphere of the complex occurs to a small extent:

Ag + + 2CN -

To characterize the stability of the CS, we introduce instability constant equal to:

The instability constant is a measure of the strength of the CS. The smaller the K is, the more firmly the COP.

Isomerism of complex compounds. For complex compounds, isomerism is very common and there are:

1. solvate isomerism is found in isomers when the distribution of water molecules between the inner and outer spheres is not the same.

Cl 3 Cl 2 H 2 O Cl (H 2 O) 2

purple light green dark green

2.Ionization isomerism is related to the different ease of dissociation of ions from the inner and outer spheres of the complex.

4 Cl 2 ]Br 2 4 Br 2 ]Cl 2

SO 4 and Br - sulfate bromo-pentammine-cobalt (III) and bromide sulfate-pentammine-cobalt (III).

C and NO 2 - chloride nitro-chloro-diethylenediamino-cobalt (III) initrite dichloro-diethylenediamino-cobalt (III).

3. Coordination isomerism found only in bicomplex compounds

[Co(NH 3) 6] [Co(CN) 6]

Coordination isomerism occurs in those complex compounds where both the cation and the anion are complex.

For example, tetrachloro-(II)platinate tetrammine-chromium(II) and tetrachloro-(II)tetrammine-platinum(II) chromate are coordination isomers

4. Communication isomerism occurs only when monodentate ligands can be coordinated through two different atoms.

5. Spatial isomerism due to the fact that the same ligands are located around the CO or near (cis), or vice versa ( trance).

Cis isomer (orange crystals) Trans isomer (yellow crystals)

Isomers of dichloro-diammine-platinum

With a tetrahedral arrangement of ligands, cis-trans isomerism is impossible.

6. Mirror (optical) isomerism, for example, in the dichloro-diethylenediamino-chromium(III) + cation:

As in the case of organic substances, mirror isomers have the same physical and chemical properties and differ in the asymmetry of crystals and the direction of rotation of the light polarization plane.

7. Ligand isomerism , for example, for (NH 2) 2 (CH 2) 4 the following isomers are possible: (NH 2) - (CH 2) 4 -NH 2, CH 3 -NH-CH 2 -CH 2 -NH-CH 3, NH 2 -CH(CH 3) -CH 2 -CH 2 -NH 2

The problem of communication in complex compounds. The nature of the coupling in the CS is different, and three approaches are currently used for explanation: the VS method, the MO method, and the method of the crystal field theory.

Sun method introduced by Pauling. The main provisions of the method:

1. A bond in a CS is formed as a result of a donor-acceptor interaction. The ligands provide electron pairs, while the complexing agent provides free orbitals. A measure of bond strength is the degree of orbital overlap.

2. CO orbitals undergo hybridization; the type of hybridization is determined by the number, nature, and electronic structure of the ligands. Hybridization of CO is determined by the geometry of the complex.

3. Additional strengthening of the complex occurs due to the fact that, along with the s-bond, a p-bond is formed.

4. The magnetic properties of the complex are determined by the number of unpaired electrons.

5. During the formation of a complex, the distribution of electrons in orbitals can remain both at neutral atoms and undergo changes. It depends on the nature of the ligands, its electrostatic field. A spectrochemical series of ligands has been developed. If the ligands have a strong field, then they displace electrons, causing them to pair and form a new bond.

Spectrochemical series of ligands:

CN - >NO 2 - >NH 3 >CNS - >H 2 O>F - >OH - >Cl - >Br -

6. The VS method makes it possible to explain bond formation even in neutral and classter complexes

K 3 K 3

1. Ligands create a strong field in the first CS, and a weak field in the second

2. Draw the valence orbitals of iron:

3. Consider the donor properties of ligands: CN - have free electron orbitals and can be donors of electron pairs. CN - has a strong field, acts on 3d orbitals, compacting them.

As a result, 6 bonds are formed, while the inner 3 d orbitals participate in the bond, i.e. an intraorbital complex is formed. The complex is paramagnetic and low-spin, since there is one unpaired electron. The complex is stable, because occupied inner orbitals.

Ions F - have free electron orbitals and can be donors of electron pairs, have a weak field, and therefore cannot condense electrons at the 3d level.

As a result, a paramagnetic, high-spin, outer-orbital complex is formed. Unstable and reactive.

Advantages of the VS method: informative

Disadvantages of the VS method: the method is suitable for a certain range of substances, the method does not explain the optical properties (coloration), does not make an energy assessment, because in some cases a quadratic complex is formed instead of the more energetically favorable tetrahedral one.