Complex compounds are classified according to the charge of the complexes: cationic - 2+, anionic - 3-, neutral - 0;

by composition and chemical properties: acids - H, bases - OH, salts - SO4;

by the type of ligands: hydroxo complexes - K2, aqua complexes - Cl3, acido complexes (ligands - acid anions) - K4, mixed-type complexes - K, Cl4.

The names of the complexes are built according to the general IUPAC rules: read and write from right to left, ligands - with the ending - o, anions - with the ending - at. Some ligands may have specific names. For example, the molecules - ligands H2O and NH3 are called aquo and amine, respectively.

Complex cations. Initially, the negatively charged ligands of the inner sphere with the ending "o" (chloro-, bromo-, nitro-, rhodano-, etc.) are called. If their number is more than one, then the numerals di-, tri-, tetra-, penta-, hexa-, etc. are added before the names of the ligands. Then they call neutral ligands, and the water molecule is called "aquo", the ammonia molecule is called "ammine". If the number of neutral ligands is more than one, then add the numerals di-, tri-, tetra-, etc.

Nomenclature of complex compounds

When composing the name of a complex compound, its formula is read from right to left. Let's consider specific examples:

Anionic complexes

Cationic complexes

K3 potassium hexacyanoferrate (III)

Na sodium tetrahydroxoaluminate

Na3 sodium hexanitrocobaltate (III)

SO4 tetraamminecopper (II) sulfate

Cl3 hexaaquachromium (III) chloride

OH hydroxide of diammine silver (I)

In the names of complex compounds, the number of identical ligands is indicated by numeric prefixes, which are written together with the names of the ligands: 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa, 7 - hepta, 8 - octa.

The names of negatively charged ligands, anions of various acids, consist of the full name (or root of the name) of the anion and the ending with the vowel -o. For example:

I- iodo-

H- hydrido-

CO32- carbonate

Some anions that act as ligands have special names:

OH-hydroxo

S2- thio-

CN- cyano-

NO- nitroso-

NO2- nitro-

In the names of neutral ligands, special prefixes are usually not used, for example: N2H4 - hydrazine, C2H4 - ethylene, C5H5N - pyridine.

By tradition, special names have been left for a small number of ligands: H2O - aqua, NH3 - amine, CO - carbonyl, NO - nitrosyl.

The names of positively charged ligands end in -th: NO + - nitrosilium, NO2 + - nitroilium, etc.

If an element that is a complexing agent is part of a complex anion, then the suffix -at is added to the root of the name of the element (Russian or Latin) and the oxidation state of the element-complexing agent is indicated in brackets. (Examples are shown in the table above). If an element, which is a complexing agent, is part of a complex Katina or a neutral complex without an external sphere, then the Russian name of the element with an indication of its oxidation state remains in the name. For example: - tetracarbonyl nickel (0).

Many organic ligands have a complex composition, therefore, when drawing up the formulas of complexes with their participation, for convenience, their letter designations are used:

C2O42-oxalato-ox

C5H5N pyridine py

(NH2) 2CO urea ur

NH2CH2CH2NH2 ethylenediamine en

C5H5- cyclopentadienyl- cp

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

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, the roots of the Latin names of the elements of the central complexing atom are used for anionic complexes. For example, - dichlorodiammineplatinum, 2- - tetrachloroplatinate (II) –ion, + - cation of diammine silver (I), - - 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- - carbonato, 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, in alphabetical order, the inner-sphere neutral molecules are indicated. 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. In-sphere 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 prefixed with the prefixes "bis", "tris", "tetrakis", etc.

The names of complex compounds with the outer sphere consist of two words (in general, "cation anion"). The name of the complex anion ends with the suffix –at. The oxidation state of the complexing agent is indicated in 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 pentacyanomonoamminferrate (II),

H 3 O - oxonium tetrachloroaurate (III),

K - 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 - diamminesilver (I) chloride,

Br - 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:

- trifluorotriaquocobalt,

- tetrachlorodiammine platinum,

- bis (cyclopentadienyl) iron.

The name of compounds with a complex cation and anion consists of the names of the cation and anion, for example:

hexanitrocobaltate (III) hexaamminecobalt (III),

trichloroammine platinum (II) chlorotriammine platinum (II).

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

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

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

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

3- - hexanitrocobaltate (III) -ion,

3- - hexanitrite-cobaltate (III) -ion.

Classification of complex compounds

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

Cationic 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 aqua complexes. These compounds include crystalline hydrates. For example: MgCl 2 × 6H 2 O

or Cl 2,

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 sulfate) also retain crystallization water, which is not part of the inner sphere, which is less firmly bound and is easily split off when heated.

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

Cl 2.

Anionic 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 external sphere and do not give complex ions in aqueous solutions: ,, carbonyl complexes,.

Cationic-anionic 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 chelating rings are called chelating (chelating) reagents. Closure of the chelate cycle by such ligands is called chelation(by chelation). The most extensive and important class of chelates is metal chelate complexes. The ability to coordinate ligands is inherent in metals of all oxidation states. In the 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 is possible and b) neutral electron-donating groups, for example, R 2 CO, R 3 N. Bidentate ligands occupy two places in the internal coordination sphere of the chelate, such as ethylenediamine (Fig. 3).

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

Fig. 3. Copper (II) bisethylenediamine cation.

Chelates in which, when the chelate ring closes, the ligand uses 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 connections. Thus, polydentate ligands with acidic functional groups can form intracomplex compounds. Intracomplex compounds are a chelate in which the ring closure is accompanied by the displacement of one or more protons from the acid functional groups by a metal ion, in particular, the intracomplex compound is copper (II) glycinate:

Fig. 4. Intra-complex compound of 8-hydroxyquinoline with zinc.

Hemoglobin and chlorophyll are also intracomplex compounds.

The most important feature of chelates is their increased stability in comparison with similarly constructed non-cyclic complexes.

Complex compounds

Summary of the lesson-lecture

Goals. Form an idea of ​​the composition, structure, properties and nomenclature of complex compounds; develop skills for determining the oxidation state of a complexing agent, drawing up equations for the dissociation of complex compounds.
New concepts: complex compound, complexing agent, ligand, coordination number, external and internal spheres of the complex.
Equipment and reagents. A rack with test tubes, concentrated ammonia solution, solutions of copper (II) sulfate, silver nitrate, sodium hydroxide.

DURING THE CLASSES

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

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? To what class of compounds can it be attributed? Can ammonia react with other salts? Are there any 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 about complex compounds.

Let's continue our experience. Divide the resulting solution into two parts. Add alkali to one part. The 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. Hence, 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 verified by adding a solution of barium chloride to the ammonia solution. A white precipitate of BaSO 4 will precipitate immediately.

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 the addition of four ammonia molecules to the copper ion. When water evaporates, ions 2+ bind with ions, and dark blue crystals are released from the solution, the composition of which is expressed by the formula SO 4 H 2 O.

Complex compounds are those containing complex ions and molecules capable of existing 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, a Nobel Prize winner. His scientific activities 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 neutral atom. The inner sphere is made up of a certain number of ions or neutral molecules, which are firmly bound to the complexing agent. They are called ligands... The number of ligands determines coordination number(CN) complexing agent.

Complex compound example

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

Let us determine 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.)

Complexing agent - iron ion Fe 2+, ligands - cyanide ions СN -, coordination number is equal to six. Everything in square brackets is an 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 bond 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 to both the forces of electrostatic attraction and the bond formed due to the lone electron pairs of the complexing agent and free orbitals of the ligands.

Complex compounds with an outer sphere are strong electrolytes and in aqueous solutions dissociate almost entirely 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 = 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 non-electrolyte 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 -.

Consider the table showing the coordination numbers of some complexing agents.

Nomenclature of complex compounds. In a compound, the anion is first named and then the cation. When specifying the composition of the inner sphere, anions are first of all called, adding the suffix - O-, for example: Cl - - chloro, CN - - cyano, OH - - hydroxo, etc. Hereinafter, neutral ligands are called and primarily ammonia and its derivatives. In this case, they use the terms: for coordinated ammonia - ammin, 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 (in Roman numerals) is indicated in brackets. 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, since it is unambiguously determined from the condition that the complex is electrically neutral.

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

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

The oxidation state of the cobalt ion is found in a similar way:

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 are there around 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 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,
- dichlorotetraamminezinc,
H 2 - hexachloro tin acid.

Using the example of several complex compounds, we will determine the structure of molecules (ion-complexing agent, its SO, coordination number, ligands, inner and outer spheres), give a name to 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 participates in the "silver mirror" reaction),

OH + + OH -.

Na - tetrahydroxoaluminate sodium,

Na Na + + -.

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

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

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

Complex compounds are widely used:

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

Chapter 17 Complex Joints

17.1. Basic definitions

In this chapter, you will become familiar with a special group of complex substances called complex(or coordinating) connections.

There is currently a strict definition of the concept " complex particle " no. The following definition is commonly used.

For example, a hydrated copper ion 2 is a complex particle, since it actually exists in solutions and some crystal hydrates, is formed from Cu 2 ions and H 2 O molecules, water molecules are actually existing 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 are found 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 referred to 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 by the donor-acceptor mechanism. In most complex particles it is, but, for example, in potassium alum SO 4 in the complex particle 3, the bond between the Al and O atoms is indeed formed by the donor-acceptor mechanism, and 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.

Usually a 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 can 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 their atoms, that is, by one bond), bidentate(connected with the central atom through two of its atoms, that is, two -bonds), tridentate etc.

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

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

There are 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 concept of a coordination polyhedron (polyhedron) is used.

Coordination polyhedra also include a square (CN = 4), a triangle (CN = 3) and a dumbbell (CN = 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 Fig. 1.

How chemical substances are complexed compounds are divided into ionic compounds (they are sometimes called ionogenic) and molecular ( nonionic) 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 chemical substances.

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

By the number of central atoms complex particles are divided into single-core and multicore... 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:

By the type of ligands, complex particles are divided into

1) Aqua complexes, that is, complex particles in which water molecules are present as ligands. More or less stable cationic aqua complexes m, anionic aquacomplexes are unstable. All crystal hydrates refer to compounds containing aqua complexes, for example:

Mg (ClO 4) 2. 6H 2 O is actually (ClO 4) 2;
BeSO 4. 4H 2 O is actually SO 4;
Zn (BrO 3) 2. 6H 2 O is actually (BrO 3) 2;
CuSO 4. 5H 2 O is actually SO 4. H 2 O.

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 exhibiting 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 molecule), for example: 2,, 3.

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

2 + 4NH 3 = 2 + 4 H 2 O

In this case, the color of the solution changes from blue to ultramarine.

4) Acidocomplexes, that is, complex particles in which acid residues of both anoxic 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 acidocomplexes:

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.
(During the development of photographic film and photographic paper, the underexposed part of the silver bromide contained in the photographic emulsion is not reduced by the developer. To remove it, this reaction is used (the process is called "fixation", since the unremoved silver bromide subsequently gradually decomposes in the light, destroying the image)

5) Complexes in which the ligands are hydrogen atoms are divided into two completely different groups: hydride complexes and complexes that are part of oniev connections.

In the formation of hydride complexes -,, -, the central atom is an electron acceptor, and a 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 the complex is formed, carbon monoxide molecules), for example:,, etc.

7) Anionhalogenate complexes - complexes of the type.

Other classes of complex particles are distinguished by the type of ligands. In addition, there are complex particles with different types of ligands; the simplest example is the aqua-hydroxocomplex.

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

The formula of a complex particle is written in square brackets in the following sequence: in the first place is the symbol of the complexing element, 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, which were anions before the formation of the complex.

The name of a complex compound is constructed 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, Russian names of elements are used in cations, and Latin names in anions.

The most common ligands are:

Examples of names for complex cations:

Examples of names for complex anions:

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

Examples of names for neutral complex particles:

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

In crystalline complexes with charged complexes, the bond between the complex and the outer-sphere ions is ionic, and the bonds between the rest of the 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, bonds between the central atom and the ligands are covalent. All of them 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 aqua complexes of alkaline and alkaline earth elements, as well as ammonium), ligands are held together by electrostatic attraction. A bond in complex particles is often referred to as a donor-acceptor or coordination bond.

Let us consider its formation using the example of the iron (II) aquacation. 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 diagram of the 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 coordination polyhedron is octahedron. All Fe-O bonds are the same. Supposed sp 3 d 2 -hybridization of the AO of the iron atom. 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 obtained by adding a solution of potassium cyanide KCN to the FeCl 2 solution:

2 + 6CN = 4 + 6H 2 O.

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

Stronger CN ligands form stronger bonds with the iron atom, the gain in energy is enough to "break" 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 aqua complex, but the type of hybridization is different - d 2 sp 3 .

The "strength" of a ligand depends primarily on the electron density of the cloud of a 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 arranged in a row in order to increase their "strength" (a kind of "row of activity" of ligands), this row is called spectrochemical range of ligands:

For complexes 3 and 3, education schemes are 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 dsp 2 -hybridization), for example, 2.

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

If the complex compound is acid, then it is a strong acid; if the base, then the base is also 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 common metabolic reactions, for example:

SO 4 + BaCl 2 = 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 insoluble ultramarine-colored substance is called "Prussian blue" [the systematic name is iron (III) -potassium hexacyanoferrate (II)].

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

2 + 4NH 3 = 2 + 4H 2 O,

as well as acid-base reactions like

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

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

Zn (OH) 2 + 2H 2 O

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

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

To assess the possibility of the ligand substitution reaction, the spectrochemical series can be used, guided by the fact that stronger ligands displace less strong ligands from the inner sphere.

Isomerism of complex compounds is related
1) with a 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.

Hydration 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 sphere, for example: SO 4 (purple) and Br (red). The first of these compounds forms a precipitate by 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 (impossible for tetrahedral). Example: cis-trans isomerism of a square complex

Optical (mirror) isomerism in essence 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. connections of the first order, i.e. compounds obeying the theory of valence;

2. higher order compounds, i.e. compounds that do not obey the concepts of valence theory. Higher-order compounds include hydrates, ammonia, etc.

CoCl 3 + 6 NH 3 = Co (NH 3) 6 Cl 3

Werner (Switzerland) introduced the concept of higher-order compounds into chemistry and gave them a name complex compounds... He attributed all the most stable higher-order compounds to CS, which in an aqueous solution either do not disintegrate into their constituent parts at all, or disintegrate to an insignificant extent. In 1893, Werner suggested that any element after saturation is capable of exhibiting additional valence as well - coordination... According to Werner's coordination theory, each COP is distinguished:

Cl 3: complexing agent (KO = Co), ligands (NH 3), coordination number (CN = 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... Ligands can be anions: Г -, ОН-, СN-, CNS-, NO 2 -, CO 3 2-, C 2 O 4 2-, neutral molecules: Н 2 О, СО, Г 2, NH 3, N 2 H 4. Coordination number - 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 symmetric configuration of the complex - octahedral (6), tetrahedral (4) and linear (2). KCH depending on the nature of the complexing agent and ligands, as well as on the size of KO and ligands. Coordination capacity of ligands- the number of sites in the inner sphere of the complex occupied by each ligand. For most ligands, the coordination capacity is equal to unity ( monodentate ligands), less often two ( bidentate ligands), there are ligands with a higher capacity (3, 4, 6) - polydental ligands... The charge of the complex must be numerically equal to the total of the outer sphere and opposite in sign. 3+ Cl 3 -.

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

Order of enumeration of ions... The first is the anion, then the cation, while the root of the Latin name KO is used in the name of the anion, and in the name of the cation, its Russian name in the genitive case.

Cl is diammine silver chloride; K 2 - potassium trichlorocuprate.

Ligand enumeration order... The ligands in the complex are listed in the following order: anionic, neutral, cationic - without hyphenation. 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. Exceptions are aqua (H 2 O), amine (NH 3). The vowel "O" is added to negatively charged anions

- hexocyanoferrate (+3) hexamine cobalt (+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 - indica, 12 - dodeca, many - poly.

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

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

In the names of complex compounds, the anionic part is indicated first 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 with an indication of 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 at first the anions are called, and then the 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 anion, the Latin name of the element is used and the oxidation state is indicated in front of 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 electroneutrality of the complex. Examples of titles:

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

OH - diammine-silver hydroxide (I).

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

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

4.on the internal structure of the COP: by the number of nuclei making up the complex:

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

5. for the absence or presence of cycles: simple and cyclic CS.

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

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

Chelated compounds are particularly strong, since the central atom in them is, as it were, blocked by a cyclic ligand. The most stable are chelates with five- and six-membered rings. Complexones 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, in analytical chemistry. Many complexes of the chelate type 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 cations Ni2 +, Pd2 +, Pt2 +, Fe2 +, etc.

Stability of complex compounds. Instability constant. Upon dissolution of the CW in water, decomposition occurs, and the inner sphere behaves as a single whole.

K = K + + -

Along with this process, dissociation of the inner sphere of the complex occurs to an insignificant 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 less K nest, the more durable the COP.

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

1.solvate isomerism is found in isomers when the distribution of water molecules between the inner and outer spheres is unequal.

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

Purple light green dark green

2.Ionization isomerism associated with 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 sulfato-pentammine-cobalt (III).

Cl and NO 2 - chloride-nitro-chloro-diethylenediamino-cobalt (III) and nitrite 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 of tetrammine-chromium (II) and - tetrachloro- (II) chromate of tetrammine-platinum (II) are coordination isomers

4. Communication isomerism arises only when monodentate ligands can coordinate through two different atoms.

5. Spatial isomerism due to the fact that the same ligands are located around the KO or near (cis), or on the contrary ( trance).

Cis isomer (orange crystals) trans isomer (yellow crystals)

Dichloro-diammine-platinum isomers

With a tetrahedral arrangement, cis-trans ligand 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, the direction of rotation of the plane of polarization of light.

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

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

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

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

2. KO orbitals undergo hybridization, the type of hybridization is determined by the number, nature and electronic structure of ligands. KO hybridization 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, 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 the orbitals can remain both for neutral atoms and undergo changes. It depends on the nature of the ligands, its electrostatic field. The spectrochemical range 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 range of ligands:

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

6. The VS method makes it possible to explain the formation of bonds even in neutral and cluster complexes

K 3 K 3

1. In the first CS, the ligands create a strong field, in the second, a weak

2. Draw the valence orbitals of iron:

3. Consider 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, densifying them.

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

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

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

Advantages of the VS method: informativeness

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