Determination of complex compounds. Chemistry lesson "complex compounds". Basic provisions and concepts of coordination theory

STATE EDUCATIONAL INSTITUTION OF HIGHER PROFESSIONAL EDUCATION

"SAMARA STATE UNIVERSITY OF TRANSPORTATIONS"

Ufa Institute of Communications

Department of General Education and Professional Disciplines

Abstract of the lecture on the discipline "Chemistry"

on the topic: "Complex Connections"

for 1st year students

railway specialties

all forms of education

Compiled by:

Abstract of a lecture on the discipline "Chemistry" on the topic "Complex compounds" for 1st year students of railway specialties of all forms of education / compiler:. - Samara: SamGUPS, 2011. - 9 p.

Approved at the meeting of the Department of OiPD on March 23, 2011, protocol

Printed by decision of the editorial and publishing council of the university.

Compiled by:

Reviewers: head. Department of "General and Engineering Chemistry" SamGUPS,

Doctor of Chemical Sciences, Professor;

Associate Professor of the Department of General and Inorganic Chemistry, Belarusian State University (Ufa),

Signed for printing on 07.04.2011. Format 60/901/16.

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Circulation 100. Order No. 73.

© Samara State University means of communication, 2011

The content of the Lecture Note corresponds to the state general educational standard and requirements of higher education to the mandatory minimum content and level of knowledge of graduates high school on the cycle "Natural sciences". The lecture is presented as a continuation Course of lectures in chemistry for students of railway specialties of the 1st year of all forms of education, compiled by the staff of the department "General and Engineering Chemistry"

The lecture contains the main provisions of the theories of chemical bonding, the stability of complexes, the nomenclature of complex compounds, examples of problem solving. The material presented in the Lecture will be a useful aid in the study of the topic "Complex Connections" by full-time and part-time students and in solving control tasks by students of the correspondence department of all specialties.

This publication is located on the institute's website.

Complex compounds

Education of many chemical compounds occurs in accordance with the valency of the atoms. Such compounds are called simple or first-order compounds. At the same time, a lot of compounds are known, the formation of which cannot be explained on the basis of the valency rules. They are formed by combining simple compounds. Such compounds are called higher order compounds, complex or coordination compounds. Examples of simple compounds: H2O, NH3, AgCl, CuSO4. Examples of complex compounds: AgCl 2NH3, Co (NO3) 3 6NH3, ZnSO4 4H2O, Fe (CN) 3 3KCN, PtCl2 2KCI, PdCl2 2NH3.

Ions of certain elements have the ability to attach polar molecules or other ions to themselves, forming complex complex ions. Compounds that contain complex ions that can exist both in a crystal and in solution are called complex compounds. The number of known complex compounds is many times greater than the number of simple compounds familiar to us. Complex compounds have been known for more than a century and a half ago. Until the nature of the chemical bond was established, the reasons for their formation, the empirical formulas of the compounds were written as we indicated in the examples above. In 1893, the Swiss chemist Alfred Werner proposed the first theory of the structure of complex compounds, which was called the coordination theory. Complex compounds constitute the most extensive and diverse class of inorganic substances. Many organoelement compounds also belong to them. The study of the properties and spatial structure of complex compounds gave rise to new ideas about the nature of the chemical bond.

1. coordination theory

In the molecule of a complex compound, the following structural elements are distinguished: the complexing ion, the attached particles coordinated around it - ligands, which together with the complexing agent internal coordination sphere, and the rest of the particles included in outer coordination sphere. When the complex compounds are dissolved, the ligands remain in a strong bond with the complexing ion, forming an almost non-dissociating complex ion. The number of ligands is called coordination number(c. h.).

Let us consider potassium ferrocyanide K4, a complex compound formed during the interaction 4KCN+Fe(CN)2=K4.

When dissolved, the complex compound dissociates into ions: K4↔4K++4-

Typical complexing agents: Fe2+, Fe3+, Co3+, Cr3+, Ag+, Zn2+, Ni2+.

Typical ligands: Cl-, Br-, NO2-, CN-, NH3, H2O.

The charge of the complexing agent is equal to the algebraic sum of the charges of its constituent ions, for example, 4-, x+6(-1)=-4, x=2.

The neutral molecules that make up the complex ion affect the charge. If the entire inner sphere is filled with only neutral molecules,

then the charge of the ion is equal to the charge of the complexing agent. So, for an ion 2+, the charge of copper is x=+2.

Charge of a complex ion is equal to the sum charges of ions in the outer sphere. In K4, the charge is -4, since there is 4K+ in the outer sphere, and the molecule as a whole is electrically neutral. Mutual substitution of ligands in the inner sphere is possible while maintaining the same coordination number, for example, Cl2, Cl, . The charge of the cobalt ion is +3.

Nomenclature of complex compounds

When composing the names of complex compounds, the anion is first indicated, and then in the genitive case - the cation (similar to simple compounds: potassium chloride or aluminum sulfate). In brackets, a Roman numeral indicates the degree of oxidation of the central atom. Ligands are called as follows: H2O - aqua, NH3 - ammine, C1- -chloro-, CN - cyano-, SO4 2- - sulfate - etc. Let's call the above compounds a) AgCl 2NH3, Co (NO3) 3 6NH3, ZnSO4 4H2O; b) Fe (CN)3 3KCN, PtCl2 2KCI; c) PdCl2 2NH3.

With a complex cation a): diamminesilver(I) chloride, hexamminecobalt(III) nitrate, tetraquozinc(P) sulfate.

FROM complex anion b): potassium hexacyanoferrate (III), potassium tetrachloroplatinate (II).

Complex- non-electrolyte c): dichlorodiamminepalladium.

In the case of non-electrolytes, the name is constructed in the nominative case and the degree of oxidation of the central atom is not indicated.

2. Methods for establishing coordination formulas

There are a number of methods for establishing the coordination formulas of complex compounds.

With the help of double exchange reactions. It was in this way that the structure of the following platinum complex compounds was proved: PtCl4 ∙ 6NH3, PtCl4 ∙ 4NH3, PtCl4 ∙ 2NH3, PtCl4 ∙ 2KCl.

If you act on the solution of the first compound with a solution of AgNO3, then all the chlorine contained in it precipitates in the form of silver chloride. Obviously, all four chloride ions are in the outer sphere and hence the inner sphere consists of only ammonia ligands. Thus, the coordination formula of the compound will be Cl4. In the compound PtCl4 ∙ 4NH3, silver nitrate precipitates only half of the chlorine, i.e., only two chloride ions are in the outer sphere, and the remaining two, together with four ammonia molecules, are part of the inner sphere, so that the coordination formula has the form Cl2. A solution of the compound PtCl4 ∙ 2NH3 does not precipitate with AgNO3, this compound is represented by the formula. Finally, silver nitrate also does not precipitate AgCl from a solution of the compound PtCl4 ∙ 2KCl, but it can be established by exchange reactions that there are potassium ions in the solution. On this basis, its structure is represented by the formula K2.

According to the molar electrical conductivity of dilute solutions. At high dilution, the molar electrical conductivity of the complex compound is determined by the charge and the number of ions formed. For compounds containing a complex ion and singly charged cations or anions, the following approximate relationship holds:

The number of ions into which it decays

electrolyte molecule

Λ(V), Ohm-1 ∙ cm2 ∙ mol-1

Measurement of the molar electrical conductivity Λ(B) in a series of complex compounds of platinum(IV) makes it possible to compose the following coordination formulas: Cl4 - dissociates with the formation of five ions; Cl2 - three ions; - neutral molecule; K2 - three ions, two of which are potassium ions. There are a number of other physicochemical methods for establishing the coordination formulas of complex compounds.

3. Type of chemical bond in complex compounds

a) Electrostatic representations .

The formation of many complex compounds can, in a first approximation, be explained by electrostatic attraction between the central cation and anions or polar ligand molecules. Along with attractive forces, there are also electrostatic repulsion forces between like-charged ligands. As a result, a stable grouping of atoms (ions) is formed, which has a minimum potential energy. The complexing agent and ligands are considered as charged non-deformable spheres of certain sizes. Their interaction is taken into account according to the Coulomb law. Thus, the chemical bond is considered ionic. If the ligands are neutral molecules, then this model should take into account the ion–dipole interaction of the central ion with the polar ligand molecule. The results of these calculations satisfactorily convey the dependence of the coordination number on the charge of the central ion. With an increase in the charge of the central ion, the strength of complex compounds increases, an increase in its radius causes a decrease in the strength of the complex, but leads to an increase in the coordination number. With an increase in the size and charge of the ligands, the coordination number and stability of the complex decrease. Primary dissociation proceeds almost completely, like the dissociation of strong electrolytes. The ligands located in the inner sphere are much stronger bound to the central atom, and are split off only to a small extent. The reversible disintegration of the inner sphere of a complex compound is called secondary dissociation. For example, the dissociation of the Cl complex can be written as follows:

Cl→++Cl - primary dissociation

+↔Ag++2NH3 secondary dissociation

However, a simple electrostatic theory is unable to explain the selectivity (specificity) of complex formation, since it does not take into account the nature of the central atom and ligands, the structural features of their electron shells. To take into account these factors, the electrostatic theory was supplemented polarizing ideas according to which complex formation is favored by the participation of small multiply charged cations of d-elements as central atoms, which have a strong polarizing effect, and as ligands by large, easily polarizable ions or molecules. In this case, the deformation of the electron shells of the central atom and ligands occurs, leading to their interpenetration, which causes strengthening of bonds.

b) The method of valence bonds.

In the method of valence bonds, it is assumed that the central atom of the complexing agent must have free orbitals for the formation of covalent bonds with ligands, the number of which determines the maximum value of the complexing agent's efficiency. In this case, a covalent σ-bond arises when the free orbital of the complexing agent atom overlaps with filled donor orbitals, i.e., containing unshared pairs of electrons. This connection is called coordination connection.

Example1. The complex ion 2+ has a tetrahedral structure. What orbitals of the complexing agent are used to form bonds with NH3 molecules?

Solution. The tetrahedral structure of molecules is characteristic of the formation of sp3 hybrid orbitals.

Example 2. Why does the complex ion + have a linear structure?

Solution. The linear structure of this ion is a consequence of the formation of two hybrid sp-orbitals by the Cu+ ion, which receive NH3 electron pairs.

Example3. Why is the ion 2-paramagnetic and 2-diamagnetic?

Solution. Cl - ions weakly interact with Ni2+ ions. Electron pairs of chlorine enter the orbitals of the next vacant layer with n=4. In this case, the 3d electrons of nickel remain unpaired, which causes the 2- paramagnetism.

In 2- due to dsp2 hybridization, electron pairing occurs and the ion is diamagnetic

c) Crystal field theory.

Crystal field theory considers the electrostatic interaction between positively charged complexing metal ions and lone electron pairs of ligands. Under the influence of the ligand field, the d-levels of the transition metal ion are split. Usually there are two configurations of complex ions - octahedral and tetrahedral. The value of the cleavage energy depends on the nature of the ligands and on the configuration of the complexes. The population of split d-orbits with electrons is carried out in accordance with the Hund rule, and the OH-, F-, Cl - ions and the H2O, NO molecules are weak field ligands, and the CN-, NO2- ions and the CO molecule are strong field ligands that significantly split d levels of the complexing agent. Schemes of splitting of d-levels in the octahedral and tetrahedral fields of ligands are given.

Example1. Draw the distribution of titanium electrons in the octahedral 3+ complex ion.

Solution. The ion is paramagnetic in accordance with the fact that there is one unpaired electron localized on the Ti3+ ion. This electron occupies one of the three degenerate dε orbitals.

When light is absorbed, the transition of an electron from the dε- to the dy-level is possible. Indeed, the 3+ ion, which has a single electron in the dε orbital, absorbs light with a wavelength of λ=4930Å. This causes dilute solutions of Ti3+ salts to become purple in addition to the absorbed one. The energy of this electronic transition can be calculated from the relation

https://pandia.ru/text/78/151/images/image002_7.png" width="50" height="32 src=">; E=40 kcal/g ion = 1.74 eV = 2, 78∙10-12 erg/ion Substituting into the formula for calculating the wavelength, we get

DIV_ADBLOCK332">

The equilibrium constant in this case is called the instability constant of the complex ion https://pandia.ru/text/78/151/images/image005_2.png" width="200" height="36 src="> 2.52∙10-3 g∙ion/l and, therefore, =10.1∙10-3 mol/l.

Example2. Determine the degree of dissociation of the 2+ complex ion in a 0.1 molar SO4 solution.

Solution. Let us denote the concentration of , formed during the dissociation of the complex ion, through x. Then \u003d 4x, and 2 + \u003d (0.1- x) mol / l. Let us substitute the equilibrium concentrations of the components into the equation Because x<<0,1, то 0,1–х ≈ 0,1. Тогда 2,6∙10-11=256х5, х=2,52∙10-3 моль/л и степень диссоциации комплексного иона

α=2.52∙10-3/0.1=0.025=2.5%.

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When considering the types of chemical bonds, it was noted that attractive forces arise not only between atoms, but also between molecules and ions. Such an interaction can lead to the formation of new, more complex complex (or coordination) compounds.

Comprehensive called compounds that have aggregates of atoms (complexes) in the nodes of the crystal lattice, capable of independent existence in solution and possessing properties that are different from the properties of their constituent particles (atoms, ions or molecules).

In the molecule of a complex compound (for example, K 4 ), the following structural elements are distinguished: ion- complexing agent (for a given Fe complex), the attached particles coordinated around it are ligands or addends (CN -), which together with the complexing agent internal coordination sphere (4-), and other particles included in outer coordination sphere (K+). When the complex compounds are dissolved, the ligands remain in a strong bond with the complexing ion, forming an almost non-dissociating complex ion. The number of ligands is called coordination number (in the case of K 4 the coordination number is 6). The coordination number is determined by the nature of the central atom and ligands, and also corresponds to the most symmetrical geometric configuration: 2 (linear), 4 (tetrahedral or square) and 6 (octahedral configuration).

Typical complexing agents are cations: Fe 2+, Fe 3+, Co 3+, Co 2+, Cu 2+, Ag +, Cr 3+, Ni 2+. The ability to form complex compounds is associated with the electronic structure of atoms. Particularly easy to form complex ions are elements of the d-family, for example: Ag +, Au +, Cu 2+, Hg 2+, Zn 2+, Fe 2+, Cd 2+, Fe 3+, Co 3+, Ni 2+, Pt 2+, Pt 4+, etc. Complexing agents can be Al 3+ and some non-metals, for example, Si and B.

Ligands can serve as charged ions: F -, OH -, NO 3 -, NO 2 -, Cl -, Br -, I -, CO 3 2-, CrO 4 2-, S 2 O 3 2-, CN -, PO 4 3- and others, and electrically neutral polar molecules: NH 3, H 2 O, PH 3, CO, etc. If all the ligands of the complexing agent are the same, then the complex homogeneous connection, for example Cl 2 ; if the ligands are different, then the compound heterogeneous, e.g. Cl. Coordination (donor-acceptor) bonds are usually established between the complexing agent and ligands. They are formed as a result of the overlapping of the ligand orbitals filled with electrons by the vacant orbitals of the central atom. In complex compounds, the donor is the complexing agent, and the acceptor is the ligand.

The number of chemical bonds between the complexing agent and the ligands determines the coordination number of the complexing agent. Characteristic coordination numbers: Cu +, Ag +, Au + = 2; Cu 2+, Hg 2+, Pb 2+, Pt 2+, Pd 2+ =4; Ni 2+, Ni 3+, Co 3+, A1 3+ = 4 or 6; Fe 2+ , Fe 3+ , Pt 4+ , ​​Pd 4+ , ​​Ti 4+ , ​​Pb 4+ , ​​Si 4+ =6.

The charge of the complexing agent is equal to the algebraic sum of the charges of its constituent ions, for example: 4-, x + 6(-1) = 4-; x=2.

The neutral molecules that make up the complex ion do not affect the charge. If the entire inner sphere is filled only with neutral molecules, then the charge of the ion is equal to the charge of the complexing agent. So, the 2+ ion has a copper charge x = 2+. The charge of the complex ion is equal to the charges of the ions in the outer sphere. In K 4, the charge is -4, since there are 4 K + cations in the outer sphere, and the molecule as a whole is electrically neutral.

Ligands in the inner sphere can replace each other while maintaining the same coordination number.

Classification and nomenclature of complex compounds. FROM points of view charge of a complex particle All complex compounds can be divided into cationic, anionic and neutral.

Cation complexes form metal cations coordinating neutral or anionic ligands around themselves, and the total charge of the ligands is less in absolute value than the oxidation state of the complexing agent, for example Cl 3 . Cationic complex compounds, in addition to hydroxo complexes and salts, can be acids, for example H - hexafluoroantimony acid.

IN anion complexes , on the contrary, the number of anion ligands is such that the total charge of the complex anion is negative, for example, . IN anion complexes hydroxide anions act as ligands hydroxocomplexes (for example, Na 2 - potassium tetrahydroxozincate), or anions of acid residues are acidocomplexes(for example, K 3 - potassium hexacyanoferrate (III)) .

Neutral complexes can be of several types: a complex of a neutral metal atom with neutral ligands (for example, Ni (CO) 4 - nickel tetracarbonyl, [Cr (C 6 H 6) 2] - dibenzenechromium). In neutral complexes of another type, the charges of the complexing agent and ligands balance each other (for example, hexaammineplatinum (IV) chloride, trinitrotriamminecobalt).

Complex compounds can be classified the nature of the ligand. Among compounds with neutral ligands, aqua complexes, ammoniates, and metal carbonyls are distinguished. Complex compounds containing water molecules as ligands are called aquacomplexes . When a substance crystallizes from a solution, the cation captures some of the water molecules that enter the crystal lattice of the salt. Such substances are called crystalline hydrates, e.g. A1C1 3 · 6H 2 O. Most crystalline hydrates are aqua complexes, so they are more accurately depicted as a complex salt ([A1(H 2 O) 6] C1 3 - hexaaqua aluminum chloride). Complex compounds with ammonia molecules as a ligand are called ammonia , for example C1 4 - hexaammineplatinum (IV) chloride. metal carbonyls are called complex compounds in which carbon monoxide (II) molecules serve as ligands, for example, iron pentacarbonyl, nickel tetracarbonyl.

Complex compounds with two complex ions in the molecule are known, for which there is a phenomenon of coordination isomerism, which is associated with a different distribution of ligands between complexing agents, for example: - hexanitrocobaltate (III) hexaammine nickel (III).

When compiling names of the complex compound the following rules apply:

1) if the compound is a complex salt, then the anion in the nominative case is called first, and then the cation in the genitive case;

2) when naming a complex ion, first the ligands are indicated, then the complexing agent;

3) molecular ligands correspond to the names of molecules (except for water and ammonia, the terms "aqua" And "amine");

4) the ending - o is added to the anionic ligands, for example: F - - fluoro, C1 - - chloro, O 2 - - oxo, CNS - - rhodan, NO 3 - - nitrato, CN - - cyano, SO 4 2- - sulfate ,S 2 O 3 2- - thiosulfate, CO 3 2- - carbonate, RO 4 3- - phosphato, OH - - hydroxo;

5) Greek numerals are used to indicate the number of ligands: 2 - di-, 3 –three-, 4 –tetra-, 5 –penta-, 6 –hexa-;

6) if the complex ion is a cation, then the Russian name of the element is used for the name of the complexing agent, if the anion is the Latin name;

7) after the name of the complexing agent, a Roman numeral in parentheses indicates its degree of oxidation;

8) in neutral complexes, the name of the central atom is given in the nominative case, and its oxidation state is not indicated.

Properties of complex compounds. Chemical reactions involving complex compounds are divided into two types:

1) outer-sphere - during their flow, the complex particle remains unchanged (exchange reactions);

2) intrasphere - during their course, changes occur in the oxidation state of the central atom, in the structure of ligands, or changes in the coordination sphere (decrease or increase in the coordination number).

One of the most important properties of complex compounds is their dissociation in aqueous solutions. Most water-soluble ionic complexes are strong electrolytes, they dissociate into outer and inner spheres: K 4 ↔ 4K + + 4 - .

Complex ions are quite stable, they are weak electrolytes, stepwise splitting off the ligands into an aqueous solution:

4 - ↔ 3- +CN - (the number of steps is equal to the number of ligands).

If the total charge of a particle of a complex compound is zero, then we have a molecule non-electrolyte, for example .

In exchange reactions, complex ions pass from one compound to another without changing their composition. The electrolytic dissociation of complex ions obeys the law of mass action and is quantitatively characterized by a dissociation constant, which is called instability constants K n. The lower the instability constant of the complex, the less it decomposes into ions, the more stable this compound. In compounds characterized by high K n, complex ions are unstable, i.e., they are practically absent in solution, such compounds are double salts . The difference between typical representatives of complex and double salts is that the latter dissociate with the formation of all the ions that make up this salt, for example: KA1 (SO 4) 2 ↔ K + + A1 3+ + 2SO 4 2- (double salt);

K ↔ 4K + + 4- (complex salt).

C 5. Ligands directly associated with the complexing agent form together with it internal (coordination) sphere of the complex. Thus, in the complex cation 2+, the inner sphere is formed by the atom of the complexing agent, copper(II), and ammonia molecules directly bound to it. The inner sphere is denoted by square brackets: 3 , 2 , 2 . Depending on the ratio of the total charge of the ligands and the complexing agent, the inner sphere may have a positive charge, for example, 3+ , either negative, for example, 3  , or zero charge, for example, as for 0 .

Ions that neutralize the charge of the inner sphere, but are not covalently bound to the complexing agent, form the outer sphere of the complex compound. For example, in the Cl 2 complex compound, two Cl  ions are in the outer sphere:

Outer sphere Cl ions are located at a greater distance from the complexing agent than NH 3 molecules, in other words, the Zn - Cl distance is greater than the length of the Zn - N chemical bond. Moreover, the chemical bond of the complex cation 2+ and chloride ions Cl - has an ionic character, while ammonia NH 3 entering the inner sphere form covalent bonds with the complexing agent Zn(II) according to the donor-acceptor mechanism (the donor of unshared electron pairs are nitrogen atoms in NH 3). So the difference between inner sphere ligands And outer sphere ions very significant.

In (OH) 2 and K 2 the outer sphere ions are OH  and K + ions, respectively. It is quite clear that in neutral complexes 0 and 0 outer sphere missing.

C 5. Usually the outer sphere is made up of simple monatomic or polyatomic ions. However, there are cases when the CS consists from two or more inner spheres, performing the functions of the cationic and anionic parts of the compound. Here each of the internal spheres is external to the other. For example, in compounds and 2, formally, the functions of outer-sphere ions can be performed by:

 complex cations 2+ and 2+,

 complex anions 2  and 4 

1.6. Multinuclear complexes

C 8. If the complex ion or neutral complex contains two or more complexing agents, then this complex is called multi-core. Among the multinuclear complexes, there are bridging, cluster and multinuclear complexes mixed type.

Atoms of the complexing agent can be bonded to each other via bridging ligands, whose functions are performed by ions OH , Cl , NH 2 , O 2 2 , SO 4 2  and some others. So, in the complex compound (NH 4) 2 bridge serve bidentate (2 bonds) hydroxide ligands:

When the atoms of the complexing agent are directly linked, the multinuclear complex is referred to as cluster type. Thus, the cluster is the complex anion 2 

in which quadruple bond Re-Re:one σ-bond, two π-bonds and one δ-bond . A particularly large number of cluster complexes are found among the derivatives d-elements.

Multinuclear complexes mixed type contain as link complexing agent–complexing agent, and bridging ligands. An example of a mixed-type complex is the cobalt carbonyl complex with the composition , having the following structure:

Here there is a single bond Co - Co and two bidentate carbonyl ligands CO, which carry out the bridge connection of complexing atoms.

complex compounds.

All inorganic compounds are divided into two groups:

1. compounds of the first order, ᴛ.ᴇ. compounds obeying the theory of valence;

2. connections of a higher order, ᴛ.ᴇ. compounds that do not obey the concepts of valence 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 attributed 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. Ligands are anions: G -, OH-, CN-, CNS-, NO 2 -, CO 3 2-, C 2 O 4 2-, neutral molecules: H 2 O, CO, G 2, NH 3, N 2 H 4 . coordination number is the number of places in the inner sphere of the complex that are 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 color or with the name of the scientist synthesizing them. Today the IUPAC nomenclature is used.

Ion listing order. It is customary to call the anion 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. The 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 ʼʼОʼʼ 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 prefixes mono-, di-, etc.

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. At the same time, before the name of the central atom, both in the anionic and in the cationic part 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: ʼʼaquaʼʼ and ʼʼamminʼʼ. If the central atom is part of the cation, then the Russian name of the element is used, followed by its oxidation state 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 are complexes in which water molecules serve as ligands, for example, Cl 2 is hexaaquacalcium chloride. Ammineates and aminates are complexes in which the ligands are molecules of ammonia and organic amines, for example: SO 4 - tetramminecopper(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. Οʜᴎ 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. For this reason, 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 [С(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 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 Pauline introduced. 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. When a complex is formed, 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 the 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 are donors of electron pairs.
Hosted on ref.rf
CN - has a strong field, acts on 3d orbitals, compacting them.

As a result, 6 bonds are formed, while the inner 3 dorbitals, ᴛ.ᴇ, participate in the connection. 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 are 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 (color), does not make an energy assessment, because in some cases a quadratic complex is formed instead of the more energetically favorable tetrahedral one.

complex compounds. - concept and types. Classification and features of the category "Complex compounds." 2017, 2018.

As you know, metals tend to lose electrons and, thereby, form. Positively charged metal ions can be surrounded by anions or neutral molecules, forming particles called comprehensive and capable of independent existence in a crystal or solution. And compounds containing complex particles in the nodes of their crystals are called complex compounds.

Structure of complex compounds

1. Most complex compounds have inner and outer spheres . When writing the chemical formulas of complex compounds, the inner sphere is enclosed in square brackets. For example, in complex compounds K and Cl 2, the inner sphere is the groups of atoms (complexes) - - and 2+, and the outer sphere is the K + and Cl ions - respectively.
2. Central atom or ion the inner sphere is called complexing agent. Usually, metal ions with a sufficient amount of free ones act as complexing agents - these are p-, d-, f- elements: Cu 2+, Pt 2+, Pt 4+, Ag +, Zn 2+, Al 3+, etc. But it can also be atoms of elements that form non-metals. The charge of the complexing agent is usually positive, but it can also be negative or zero and equal to the sum of the charges of all other ions. In the examples above, the complexing agents are Al 3+ and Ca 2+ ions.

1. The complexing agent is surrounded and is associated with ions of the opposite sign or neutral molecules, the so-called ligands. Anions such as F - , OH - , CN - , CNS - , NO 2 - , CO 3 2- , C 2 O 4 2- , etc., or neutral H 2 O molecules, can act as ligands in complex compounds, NH 3 , CO, NO, etc. In our examples, these are OH ions - and NH 3 molecules. The number of ligands in various complex compounds ranges from 2 to 12. And the number of ligands itself (the number of sigma bonds) is called coordination number (c.h.) of the complexing agent. In the considered examples, c.ch. equals 4 and 8.

1. Complex charge(inner sphere) is defined as the sum of the charges of the complexing agent and ligands.
2. outer sphere form ions associated with the complex by ionic or intermolecular bonds and having a charge whose sign is opposite to that of the charge of the complexing agent. The numerical value of the charge of the outer sphere coincides with the numerical value of the charge of the inner sphere. In the formula of a complex compound, they are written in square brackets. The outer sphere may even be absent if the inner sphere is neutral. In the given examples, the outer sphere is formed by 1 K + ion and 2 Cl - ions, respectively.

Classification of complex compounds

Based on different principles, complex compounds can be classified in different ways:

1. By electric charge: cationic, anionic and neutral complexes.

• Cation complexes have a positive charge and are formed if neutral molecules are coordinated around a positive ion. For example, Cl 3 , Cl 2
• Anion complex s have a negative charge and are formed if atoms with negative are coordinated around a positive ion. For example, K, K 2
• Neutral complexes have zero charge and no outer sphere. They can be formed upon coordination around an atom of molecules, as well as upon simultaneous coordination around a central positively charged ion of negative ions and molecules.

1. By the number of complexing agents

• single core - the complex contains one central atom, for example, K 2
• multi-core e- the complex contains two or more central atoms, for example,

1. By type of ligand

• Hydrates – contain aqua-complexes, i.e. water molecules act as ligands. For example, Br 3 , Br 2
• Ammonia - contain ammine complexes, in which ammonia molecules (NH 3) act as ligands. For example, Cl 2 , Cl
• carbonyls – in such complex compounds, carbon monoxide molecules act as ligands. For example, , .
• acidocomplexes - complex compounds containing acidic residues of both oxygen-containing and anoxic acids as ligands (F -, Cl -, Br -, I -, CN -, NO 2 -, SO 4 2–, PO 4 3–, etc., as well as OH-). For example, K 4 , Na 2
• Hydroxocomplexes - complex compounds in which hydroxide ions act as ligands: K 2, Cs 2

Complex compounds may contain ligands belonging to various classes of the above classification. For example: K, Br

1. By chemical properties:acids, bases, salts, non-electrolytes:

• acids — H, H2
• Foundations - (OH) 2,OH
• salt — Cs 3 , Cl 2
• Non-electrolytes —

1. According to the number of places occupied by the ligand in the coordination sphere

In the coordination sphere, ligands can occupy one or more places, i.e. form one or more bonds with the central atom. On this basis, they distinguish:

• Monodentate ligands - these are ligands such as molecules of H 2 O, NH 3, CO, NO, etc. and nones CN - , F - , Cl - , OH - , SCN - , etc.
• Bidentate ligands . This type of ligand includes ions H 2 N-CH 2 -COO -, CO 3 2-, SO 4 2-, S 2 O 3 2-, an ethylenediamine molecule H 2 N-CH 2 -CH 2 -H 2 N (abbreviated en).
• Polydentate ligands . These are, for example, organic ligands containing several groups - CN or -COOH (EDTA). Some polydentate ligands are capable of forming cyclic complexes called chelate (for example, hemoglobin, chlorophyll, etc.)

Nomenclature of complex compounds

To burn the formula of the complex compound, it must be remembered that, like any ionic compound, the cation formula is written first, and then the anion formula. In this case, the formula of the complex is written in square brackets, where the complexing agent is written first, then the ligands.

And here are a few rules, following which it will not be difficult to compose the name of a complex compound:

1. In the names of complex compounds, as well as ionic salts, the anion is listed first, followed by the cation.
2. In the name of the complex ligands are listed first, and then the complexing agent. The ligands are listed in alphabetical order.
3. Neutral ligands have the same name as molecules, the ending is added to anionic ligands -about. The table below lists the names of the most common ligands.

1. If the number of ligands more than one, then their number is indicated by Greek prefixes:

2-di-, 3-tri-, 4-tetra-, 5-penta-, 6-hexa-, 7-hepta-, 8-octa-, 9-nona-, 10-deca-.

If the name of the ligand itself already contains a Greek prefix, then the name of the ligand is written in brackets and a prefix of the type is added to it:

2-bis-, 3-tris-, 4-tetrakis-, 5-pentakis-, 6-hexakis-.

For example, the Cl 3 compound is called tris(ethylenediamine)cobalt(III).

1. The names of complex anions end suffix - at
2. After the name of the metal in parentheses indicate Roman numerals for its oxidation state.

For example, let's call the following connections:

• Cl

Let's start with ligands: 4 water molecules are designated as tetraaqua, and 2 chloride ions are designated as dichloro.

Finally, anion in this connection is an chloride ion.

tetraaquadichlorochromium chloride(III)

• K4

Let's start with ligands: the complex anion contains 4 ligands CN - , which are called tetracyano.

Since the metal is part of the complex anion, it is called nickelate(0).

So the full title is: potassium tetracyanonickelate(0)