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 of: "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.
Writing paper. The print is operational. Conv. oven l. 0.6.
Circulation 100. Order No. 73.
© Samara State Transport University, 2011
The content of the Lecture Note corresponds to the state the general educational standard and the requirements of higher education to the mandatory minimum content and level of knowledge of higher school graduates in 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
The formation of many chemical compounds occurs in accordance with the valence of 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.
The charge of a complex ion is equal to the sum of the charges of the 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.
WITH 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(В) in a series of platinum(IV) complex compounds 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 are 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. WITH 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).
Complex compounds
Lesson-lecture Grade 11
The lesson submitted for the competition “I'm going to the lesson”, I spend in the 11th biological and chemical class, where 4 hours a week are allotted for studying chemistry.
I took the topic “Complex compounds”, firstly, because this group of substances is of exceptionally great importance in nature; secondly, many USE tasks include the concept of complex compounds; thirdly, students from this class choose professions related to chemistry and will meet with a group of complex compounds in the future.
Target. Form the concept of the composition, classification, structure and basic nomenclature of complex compounds; consider their chemical properties and show the meaning; expand students' understanding of the diversity of substances.
Equipment. Samples of complex compounds.
Lesson plan
I. Organizational moment.
II. Learning new material (lecture).
III. Summing up and setting homework.
Lecture plan
1. Variety of substances.
2. Coordination theory of A. Werner.
3. Structure of complex compounds.
4. Classification of complex compounds.
5. The nature of the chemical bond in complex compounds.
6. Nomenclature of complex compounds.
7. Chemical properties of complex compounds.
8. The value of complex compounds.
DURING THE CLASSES
I. Organizational moment
II. Learning new material
Variety of substances
The world of substances is diverse, and we are already familiar with the group of substances that belong to complex compounds. These substances have been studied since the 19th century, but it was difficult to understand their structure from the standpoint of the existing ideas about valence.
A. Werner's coordination theory
In 1893, the Swiss inorganic chemist Alfred Werner (1866–1919) formulated a theory that made it possible to understand the structure and some properties of complex compounds and called coordination theory*. Therefore, complex compounds are often called coordination compounds.
Compounds, which include complex ions that exist both in a crystal and in solution, are called complex, or coordination.
The structure of complex compounds
According to Werner's theory, the central position in complex compounds is usually occupied by a metal ion, which is called the central ion, or complexing agent.
Complexing agent - a particle (atom, ion or molecule) that coordinates (situates) around itself other ions or molecules.
The complexing agent usually has a positive charge, is d-element, exhibits amphoteric properties, has a coordination number of 4 or 6. Molecules or acid residues - ligands (addends) are located (coordinate) around the complexing agent.
Ligands - particles (molecules and ions) coordinated by the complexing agent and having direct chemical bonds with it (for example, ions: Cl - , I - , NO 3 - , OH - ; neutral molecules: NH 3 , H 2 O, CO ).
The ligands are not bound to each other, since repulsive forces act between them. When molecules are ligands, molecular interaction is possible between them. The coordination of ligands around the complexing agent is a characteristic feature of complex compounds (Fig. 1).
Coordination number - is the number of chemical bonds that the complexing agent forms with the ligands.
 |
Rice. 2. Tetrahedral structure of the ion - |
The value of the coordination number of the complexing agent depends on its nature, degree of oxidation, nature of the ligands, and conditions (temperature, concentration) under which the complexation reaction proceeds. The coordination number can have values from 2 to 12. The most common are the coordination numbers 4 and 6. For the coordination number 4, the structure of complex particles can be tetrahedral (Fig. 2) and in the form of a flat square (Fig. 3). Complex compounds with a coordination number of 6 have an octahedral structure of 3– (Fig. 4).
 |
Rice. 4. Ion 3 - octahedral structure |
The complexing agent and its surrounding ligands constitute the interior of the complex. A particle consisting of a complexing agent and surrounding ligands is called a complex ion. When depicting complex compounds, the inner sphere (complex ion) is limited by square brackets. The remaining components of the complex compound are located in external sphere(Fig. 5).
The total charge of the ions of the outer sphere must be equal in value and opposite in sign to the charge of the complex ion:
Classification of complex compounds
A large variety of complex compounds and their properties does not allow creating a unified classification. However, substances can be grouped according to some individual features.
1) By composition.
2) According to the type of coordinated ligands.
A) Aquacomplexes- these are complex cations in which H 2 O molecules are ligands. They are formed by metal cations with an oxidation state of +2 or more, and the ability to form aqua complexes in metals of one group of the periodic system decreases from top to bottom.
Examples of aqua complexes:
Cl 3 , (NO 3) 3 .
b) Hydroxocomplexes are complex anions in which the ligands are hydroxide ions OH - . Complexing agents are metals prone to the manifestation of amphoteric properties - Be, Zn, Al, Cr.
For example: Na, Ba.
V) Ammonia are complex cations in which NH 3 molecules are ligands. Complexing agents are d-elements.
For example: SO 4 , Cl.
G) acidocomplexes are complex anions in which the ligands are anions of inorganic and organic acids.
For example: K 3 , Na 2 , K 4 .
3) By the charge of the inner sphere.
The nature of the chemical bond in complex compounds
In the inner sphere, there are covalent bonds between the complexing agent and ligands, which are also formed by the donor-acceptor mechanism. For the formation of such bonds, the presence of free orbitals in some particles (available in the complexing agent) and unshared electron pairs in other particles (ligands) is necessary. The role of the donor (supplier of electrons) is played by the ligand, and the acceptor that accepts electrons is the complexing agent. The donor-acceptor bond arises as a result of the overlapping of the free valence orbitals of the complexing agent with the filled donor orbitals.
There is an ionic bond between the outer and inner spheres. Let's take an example.
The electronic structure of the beryllium atom:
The electronic structure of the beryllium atom in an excited state:
The electronic structure of the beryllium atom in the 2– complex ion:
Dotted arrows show fluorine electrons; two of the four bonds are formed by the donor-acceptor mechanism. In this case, the Be atom is an acceptor, and fluorine ions are donors, their free electron pairs fill hybridized orbitals ( sp 3 - hybridization).
Nomenclature of complex compounds
The most widespread is the nomenclature recommended by IUPAC. Name complex anion begins with the designation of the composition of the inner sphere: the number of ligands is indicated by Greek numerals: 2-di, 3-three, 4-tetra, 5-penta, 6-hexa, etc., followed by the names of the ligands, to which the connecting vowel “o” is added »: Cl - - chloro-, CN - - cyano-, OH - - hydroxo-, etc. If the complexing agent has a variable oxidation state, then its oxidation state is indicated in brackets in Roman numerals, and its name with the suffix -at: Zn - zinc at, Fe – ferr at(III), Au - aur at(III). The last name is the cation of the outer sphere in the genitive case.
K 3 - potassium hexacyanoferrate (III),
K 4 - potassium hexacyanoferrate (II),
K 2 - potassium tetrahydroxozincate.
Names of compounds containing complex cation, are built from the names of the anions of the external environment, after which the number of ligands is indicated, the Latin name of the ligand is given (ammonia molecule NH 3 - ammine, water molecule H 2 O - aqua from the Latin name of water) and the Russian name of the complexing element; the Roman numeral in parentheses indicates the degree of oxidation of the complexing element, if it is variable. For example:
SO 4 - tetraammine copper (II) sulfate,
Cl 3 - hexaaqua aluminum chloride.
Chemical properties of complex compounds
1. In solution, complex compounds behave like strong electrolytes; completely dissociate into cations and anions:
Cl 2 \u003d Pt (NH 3) 4] 2+ + 2Cl -,
K 2 \u003d 2K + + 2–.
Dissociation of this type is called primary.
Secondary dissociation is associated with the removal of ligands from the inner sphere of the complex ion:
2– PtCl 3 – + Cl – .
Secondary dissociation occurs in steps: complex ions ( 2–) are weak electrolytes.
2. Under the action of strong acids, hydroxo complexes are destroyed, for example:
a) with a lack of acid
Na 3 + 3HCl \u003d 3NaCl + Al (OH) 3 + 3H 2 O;
b) with an excess of acid
Na 3 + 6HCl \u003d 3NaCl + AlCl 3 + 6H 2 O.
3. Heating (thermolysis) of all ammoniates leads to their decomposition, for example:
SO 4 CuSO 4 + 4NH 3.
The value of complex compounds
Coordination compounds are extremely important in nature. Suffice it to say that almost all enzymes, many hormones, drugs, biologically active substances are complex compounds. For example, blood hemoglobin, due to which oxygen is transferred from the lungs to tissue cells, is a complex compound containing iron (Fig. 6), and chlorophyll, responsible for photosynthesis in plants, is a complex magnesium compound (Fig. 7).
A significant part of natural minerals, including polymetallic ores and silicates, is also composed of coordination compounds. Moreover, chemical methods for extracting metals from ores, in particular copper, tungsten, silver, aluminum, platinum, iron, gold and others, are also associated with the formation of easily soluble, low-melting or volatile complexes. For example: Na 3 - cryolite, KNa 3 4 - nepheline (minerals, complex compounds containing aluminum).
The modern chemical industry widely uses coordination compounds as catalysts in the synthesis of macromolecular compounds, in the chemical processing of oil, and in the production of acids.
III. Summing up and setting homework
Homework.
1) Prepare for a lecture for a practical lesson on the topic: “Complex compounds”.
2) Give a written description of the following complex compounds by structure and classify according to their characteristics:
K 3, (NO 3) 3, Na 2, OH.
3) Write the reaction equations with which you can carry out transformations:
* For the discovery of this new field of science, A. Werner was awarded the Nobel Prize in 1913.
Compounds of the type BF 3, CH 4, NH 3, H 2 O, CO 2, etc., in which the element exhibits its usual maximum valence, are called valence-saturated compounds or first order compounds. When first-order compounds interact with each other, higher-order compounds are formed. TO higher order compounds include hydrates, ammoniates, addition products of acids, organic molecules, double salts, and many others. Examples of the formation of complex compounds:
PtCl 4 + 2KCl \u003d PtCl 4 ∙ 2KCl or K 2
CoCl 3 + 6NH 3 \u003d CoCl 3 ∙ 6NH 3 or Cl 3.
A. Werner introduced into chemistry ideas about compounds of a higher order and gave the first definition of the concept of a complex compound. Elements after saturation of ordinary valences are able to show additional valency - coordinating. It is due to the coordination valency that higher-order compounds are formed.
Complex compounds – complex substances that can be isolated central atom(complexing agent) and related molecules and ions - ligands.
The central atom and ligands form complex (inner sphere), which, when writing the formula of a complex compound, is enclosed in square brackets. The number of ligands in the inner sphere is called coordination number. Molecules and ions surrounding the complex form outer sphere. An example of a complex salt of potassium hexacyanoferrate (III) K 3 (the so-called red blood salt).
The central atoms can be transition metal ions or atoms of some non-metals (P, Si). Ligands can be halogen anions (F -, Cl -, Br -, I -), OH -, CN -, CNS -, NO 2 - and others, neutral molecules H 2 O, NH 3, CO, NO, F 2 , Cl 2, Br 2, I 2, hydrazine N 2 H 4, ethylenediamine NH 2 -CH 2 -CH 2 -NH 2, etc.
Coordination valence(CV) or coordination number - the number of places in the inner sphere of the complex that can be occupied by ligands. The coordination number is usually greater than the oxidation state of the complexing agent, depending on the nature of the complexing agent and ligands. Complex compounds with coordination valences of 4, 6, and 2 are more common.
Ligand coordination capacity – the number of places in the inner sphere of the complex occupied by each ligand. For most ligands, the coordination capacity is one, less often 2 (hydrazine, ethylenediamine) and more (EDTA - ethylenediaminetetraacetate).
Complex charge must be numerically equal to the total charge of the outer sphere and opposite in sign, but there are also neutral complexes. The oxidation state of the complexing agent equal and opposite in sign to the algebraic sum of the charges of all other ions.
Systematic names of complex compounds are formed as follows: first, the anion is called in the nominative case, then separately in the genitive case - the cation. The ligands in the complex are listed together in the following order: a) anionic; b) neutral; c) cationic. Anions are listed in the order H - , O 2- , OH - , simple anions, polyatomic anions, organic anions - in alphabetical order. Neutral ligands are named the same as molecules, with the exception of H 2 O (aqua) and NH 3 (ammine); negatively charged ions add the connecting vowel " O". The number of ligands is indicated by prefixes: di-, tri, tetra-, penta-, hexa- etc. The ending for anionic complexes is "- at" or "- new", if the acid is called; there are no typical endings for cationic and neutral complexes.
H - hydrogen tetrachloroaurate (III)
(OH) 2 - tetraamminecopper (II) hydroxide
Cl 4 - hexaammineplatinum (IV) chloride
– tetracarbonyl nickel
– hexacyanoferrate (III) of hexaamminecobalt (III)
Classification of complex compounds based on various principles:
By belonging to a certain class of compounds:
- complex acids– H 2 , H 2 ;
- complex bases- (OH) 2;
- complex salts- Li 3, Cl 2.
By the nature of ligands:
- aquacomplexes(water is the ligand) - SO 4 ∙ H 2 O, [Co (H 2 O) 6] Cl 2;
- ammonia(complexes in which ammonia molecules serve as ligands) - [Сu(NH 3) 4 ]SO 4, Cl;
- acidocomplexes(oxalate, carbonate, cyanide, halide complexes containing anions of various acids as ligands) - K 2, K 4;
- hydroxocomplexes(compounds with OH groups in the form of ligands) - K 3 [Al (OH) 6];
- chelated or cyclic complexes(bi- or polydentate ligand and the central atom form a cycle) - complexes with aminoacetic acid, EDTA; chelates include chlorophyll (complexing agent - magnesium) and hemoglobin (complexing agent - iron).
By the sign of the charge of the complex: cationic, anionic, neutral complexes.
A special group is made up of hypercomplex compounds. In them, the number of ligands exceeds the coordination valency of the complexing agent. So, in the CuSO 4 ∙ 5H 2 O compound, copper has a coordination valence of four and four water molecules are coordinated in the inner sphere, the fifth molecule joins the complex using hydrogen bonds: SO 4 ∙ H 2 O.
Ligands are bound to the central atom donor-acceptor bond. In an aqueous solution, complex compounds can dissociate to form complex ions:
Cl ↔ + + Cl –
To a small extent, there is a dissociation of the inner sphere of the complex:
+ ↔ Ag + + 2NH 3
The measure of the strength of the complex is complex instability constant:
K nest + \u003d C Ag + ∙ C2 NH 3 / C Ag (NH 3) 2] +
Instead of the instability constant, sometimes they use the reciprocal value, called the stability constant:
K mouth \u003d 1 / K nest
In moderately dilute solutions of many complex salts, both complex and simple ions exist. Further dilution can lead to complete decomposition of complex ions.
According to a simple electrostatic model by W. Kossel and A. Magnus, the interaction between a complexing agent and ionic (or polar) ligands obeys the Coulomb law. A stable complex is obtained when the forces of attraction to the core of the complex balance the repulsive forces between the ligands. The strength of the complex increases with an increase in the nuclear charge and a decrease in the radius of the complexing agent and ligands. The electrostatic model is very illustrative, but is unable to explain the existence of complexes with nonpolar ligands and a complexing agent in the zero oxidation state; what determines the magnetic and optical properties of compounds.
A clear way to describe complex compounds is the method of valence bonds (MBS) proposed by Pauling. The method is based on a number of provisions:
The relationship between the complexing agent and the ligands is donor-acceptor. Ligands provide electron pairs, and the core of the complex provides free orbitals. A measure of bond strength is the degree of orbital overlap.
The orbitals of the central atom involved in the formation of bonds undergo hybridization. The type of hybridization is determined by the number, nature, and electronic structure of the ligands. The hybridization of the electron orbitals of the complexing agent determines the geometry of the complex.
Additional strengthening of the complex is due to the fact that, along with σ-bonds, π-bonds can also arise.
The magnetic properties exhibited by the complex are explained on the basis of the occupancy of the orbitals. In the presence of unpaired electrons, the complex is paramagnetic. The pairing of electrons determines the diamagnetism of the complex compound.
MVS is suitable for describing only a limited range of substances and does not explain the optical properties of complex compounds, since does not take into account excited states.
A further development of the electrostatic theory on a quantum mechanical basis is the crystal field theory (TCF). According to TCP, the bond between the core of the complex and the ligands is ionic or ion-dipole. TCP pays the main attention to the consideration of those changes that occur in the complexing agent under the influence of the ligand field (splitting of energy levels). The concept of energy splitting of a complexing agent can be used to explain the magnetic properties and color of complex compounds.
TCP is applicable only to complex compounds in which the complexing agent ( d-element) has free electrons, and does not take into account the partially covalent nature of the complexing agent-ligand bond.
The molecular orbital method (MMO) takes into account the detailed electronic structure of not only the complexing agent, but also the ligands. The complex is considered as a single quantum-mechanical system. The valence electrons of the system are located in multicenter molecular orbitals covering the nuclei of the complexing agent and all ligands. According to the MMO, the increase in the splitting energy is due to the additional strengthening of the covalent bond due to π-bonding.
Complex compounds
Lecture summary
Goals. To form ideas about the composition, structure, properties and nomenclature of complex compounds; develop skills in determining the degree of oxidation of a complexing agent, compiling equations for the dissociation of complex compounds.
New concepts: complex compound, complexing agent, ligand, coordination number, outer and inner spheres of the complex.
Equipment and reagents. Stand with test tubes, concentrated ammonia solution, solutions of copper(II) sulfate, silver nitrate, sodium hydroxide.
DURING THE CLASSES
Laboratory experience. Add ammonia solution to copper(II) sulfate solution. The liquid will turn an intense blue color.
What happened? Chemical reaction? Until now, we did not know that ammonia can react with salt. What substance was formed? What is its formula, structure, name? What class of compounds does it belong to? Can ammonia react with other salts? Are there connections similar to this? We have to answer these questions today.
To better study the properties of some compounds of iron, copper, silver, aluminum, we need knowledge of complex compounds.
Let's continue our experience. The resulting solution is divided into two parts. Let's add alkali to one part. Precipitation of copper (II) hydroxide Cu (OH) 2 is not observed, therefore, there are no doubly charged copper ions in the solution or there are too few of them. From this we can conclude that copper ions interact with the added ammonia and form some new ions that do not give an insoluble compound with OH - ions.
At the same time, the ions remain unchanged. This can be seen by adding a solution of barium chloride to the ammonia solution. A white precipitate of BaSO 4 will immediately fall out.
Studies have established that the dark blue color of the ammonia solution is due to the presence of complex 2+ ions in it, formed by attaching four ammonia molecules to the copper ion. When water evaporates, 2+ ions bind to ions, and dark blue crystals stand out from the solution, the composition of which is expressed by the formula SO 4 H 2 O.
Complex compounds are compounds that contain complex ions and molecules that can exist both in crystalline form and in solutions.
Formulas of molecules or ions of complex compounds are usually enclosed in square brackets. Complex compounds are obtained from conventional (non-complex) compounds.
Examples of obtaining complex compounds
The structure of complex compounds is considered on the basis of the coordination theory proposed in 1893 by the Swiss chemist Alfred Werner, Nobel Prize winner. His scientific activity took place at the University of Zurich. The scientist synthesized many new complex compounds, systematized previously known and newly obtained complex compounds and developed experimental methods for proving their structure.
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A. Werner
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In accordance with this theory, complex compounds are distinguished complexing agent, external And inner sphere. The complexing agent is usually a cation or a neutral atom. The inner sphere is made up of a certain number of ions or neutral molecules that are firmly bound to the complexing agent. They are called ligands. The number of ligands determines coordination number(KN) complexing agent.
An example of a complex compound
Considered in the example, the compound SO 4 H 2 O or CuSO 4 5H 2 O is a crystalline hydrate of copper (II) sulfate.
Let's define the constituent parts of other complex compounds, for example K 4 .
(Reference. The substance with the formula HCN is hydrocyanic acid. Hydrocyanic acid salts are called cyanides.)
The complexing agent is an iron ion Fe 2+, the ligands are cyanide ions CN - , the coordination number is six. Everything written in square brackets is the inner sphere. Potassium ions form the outer sphere of the complex compound.
The nature of the bond between the central ion (atom) and ligands can be twofold. On the one hand, the connection is due to the forces of electrostatic attraction. On the other hand, between the central atom and ligands a bond can be formed by the donor-acceptor mechanism by analogy with the ammonium ion. In many complex compounds, the bond between the central ion (atom) and the ligands is due both to the forces of electrostatic attraction and to the bond formed due to the unshared electron pairs of the complexing agent and free orbitals of the ligands.
Complex compounds having an outer sphere are strong electrolytes and in aqueous solutions dissociate almost completely into a complex ion and ions outer sphere. For example:
SO 4 2+ + .
In exchange reactions, complex ions pass from one compound to another without changing their composition:
SO 4 + BaCl 2 \u003d Cl 2 + BaSO 4.
The inner sphere can have a positive, negative, or zero charge.
If the charge of the ligands compensates for the charge of the complexing agent, then such complex compounds are called neutral or 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 -.
Let's consider a table that shows the coordination numbers of some complexing agents.
Nomenclature of complex compounds. In a compound, the anion is named first, and then the cation. When specifying the composition of the inner sphere, first of all, anions are called, adding to the Latin name the suffix - O-, for example: Cl - - chloro, CN - - cyano, OH - - hydroxo, etc. Hereafter referred to as neutral ligands and primarily ammonia and its derivatives. In this case, the following terms are used: for coordinated ammonia - ammine, for water - aqua. The number of ligands is indicated in Greek words: 1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa. Then they move on to the name of the central atom. If the central atom is part of the cations, then the Russian name of the corresponding element is used and its oxidation state is indicated in brackets (in Roman numerals). If the central atom is contained in the anion, then use the Latin name of the element, and at the end add the ending - at. In the case of non-electrolytes, the oxidation state of the central atom is not given, because it is uniquely determined from the condition of electroneutrality of the complex.
Examples. To name the Cl 2 complex, the oxidation state is determined
(S.O.)
X complexing agent - Cu ion X+ :
1 x + 2 (–1) = 0,x = +2, C.O.(Cu) = +2.
Similarly, the oxidation state of the cobalt ion is found:
y + 2 (–1) + (–1) = 0,y = +3, S.O.(Co) = +3.
What is the coordination number of cobalt in this compound? How many molecules and ions surround the central ion? The coordination number of cobalt is six.
The name of the complex ion is written in one word. The oxidation state of the central atom is indicated by a Roman numeral placed in parentheses. For example:
Cl 2 - tetraammine copper (II) chloride,
NO 3 –
dichloroaquatriamminecobalt(III) nitrate,
K 3 - hexacyanoferrate(III)
potassium,
K 2 - tetrachloroplatinate (II)
potassium,
- dichlorotetraamminzinc,
H 2 - hexachlorotinic acid.
On the example of several complex compounds, we will determine the structure of molecules (ion-complexing agent, its S.O., coordination number, ligands, inner and outer spheres), give the name of the complex, write down the equations of electrolytic dissociation.
K 4 - potassium hexacyanoferrate (II),
K 4 4K + + 4– .
H - tetrachloroauric acid (formed by dissolving gold in aqua regia),
H H + + –.
OH - diammine silver (I) hydroxide (this substance is involved in the "silver mirror" reaction),
OH + + OH - .
Na - tetrahydroxoaluminate sodium,
Na Na + + - .
Many organic substances also belong to complex compounds, in particular, the products of the interaction of amines with water and acids known to you. For example, salts of methyl ammonium chloride and phenylammonium chloride are complex compounds. According to the coordination theory, they have the following structure:
Here, the nitrogen atom is a complexing agent, the hydrogen atoms at nitrogen, and the methyl and phenyl radicals are ligands. Together they form the inner sphere. In the outer sphere are chloride ions.
Many organic substances that are of great importance in the life of organisms are complex compounds. These include hemoglobin, chlorophyll, enzymes and others
Complex compounds are widely used:
1) in analytical chemistry for the determination of many ions;
2) for the separation of certain metals and the production of high purity metals;
3) as dyes;
4) to eliminate water hardness;
5) as catalysts for important biochemical processes.