What are complex compounds. Complex compounds

COMPLEX COMPOUNDS (coordination compounds), chemical compounds in which the central atom (complexing agent) and one or more ions and/or molecules directly associated (coordinated) can be isolated. Coordinated particles are called ligands, the number of donor atoms in them coordinated by the central atom is its coordination number. The central atom binds the ligands through both electrostatic and donor-acceptor interactions. The coordination number and oxidation state are the most important characteristics of the complexing atom.

The central atom and coordinated ligands form the inner coordination sphere of complex compounds; when writing the formula of complex compounds, it is usually enclosed in square brackets. Inside the brackets, the entry is made in the following sequence: the chemical symbol of the central atom, the symbols of anionic, then neutral ligands, indicating their number. If the inner sphere carries a charge, then it is compensated by the counterions that form the outer sphere. Cations, for example, K + in K 4, and anions, for example, SO 4 2- in SO 4, can also be outer-sphere. In addition to counterions, neutral molecules can be found in the outer sphere. Examples of complex compounds consisting only of a central atom and ligands are Ti(CO) 7 , Cr(CO) 6 and other metal carbonyls.

The names of complex compounds are built in accordance with the IUPAC nomenclature rules, starting with ligands and taking into account their charge; for example, - dichlorodiammineplatinum (II), (NO 3) 3 - hexaamminecobalt (III) nitrate, Na 2 - sodium tetrachloropalladate (II).

History reference. Among the early, scientifically documented, studies of complex compounds, one can single out the production of Cl 2 . In 1597 A. Libaviy and KFe in 1704 by the German craftsman G. Disbach, however, in accordance with the ideas existing at that time, these substances were classified as double salts. The beginning of a systematic study of complex compounds is usually considered the discovery of the French chemist B. Tasser, who in 1798 described the appearance of a brown color in ammonia solutions of cobalt chloride during the formation of hexaamminecobalt(III) chloride Cl 3 . An important feature of this study was the understanding that the resulting compound is the product of a combination of valence-saturated, very stable "simple" compounds capable of independent existence and that for aqueous solutions of the resulting "complex" or complex (from the Latin complexus - combination), compounds are characteristic properties that are different from the properties of its constituent simple compounds. In the 19th century, a large number of various complex compounds were synthesized; among experimental studies, one can single out the work of the Danish chemist V. Zeise, who obtained complex compounds of platinum with organic ligands K (Zeise's salt, 1827), and S. Jørgensen (synthesized complex compounds of cobalt, chromium, rhodium, and platinum).

During the same period, T. Graham, K. K. Klaus and other scientists made attempts to explain the existence and structure of complex compounds. Of the early theories, the most widely known is the chain theory of the Swedish chemist C. Blomstrand, developed by S. Jørgensen (Blomstrand-Jørgensen's theory, 1869), which made it possible to explain the structure of certain classes of complex compounds (in particular, ammoniates). A generalized idea of the spatial structure of complex compounds was given by the coordination theory proposed by A. Werner in 1893 (the work was awarded the Nobel Prize in 1913). The coordination theory refuted the concepts of constant and directed valency generally accepted to explain the structure of inorganic compounds. A. Werner introduced the concepts of “main” and “side” valency, coordination, coordination number, geometry of complex compounds, important for the whole historical period, created the basis for the classification of complex compounds; the question of the nature of the main and side valence was not considered in the coordination theory. The resolution of the question of the nature of the coordination bond became possible after the creation of the electronic theory of valency (G. Lewis, 1916). The main merit in using this theory to explain the nature of the coordination bond belongs to the English chemist N. Sidgwick. According to the concept of Sidgwick (1923), the main valences were interpreted as the result of electron transfer, the side ones - as the result of the socialization of electron pairs. The development of modern ideas about the nature of the coordination bond is associated with the use of quantum chemical approaches - the theory of the crystal field, the method of valence bonds, the method of molecular orbitals, the theory of the field of ligands; the main contribution to the spread of the method of valence bonds to complex compounds belongs to L. Pauling, the theory of the crystal field - to the American chemist L. Orgel. The development of the chemistry of complex compounds was promoted by the studies of the American scientists J. Beilar, R. Pearson, G. Gray, and the Russian chemists I. I. Chernyaev, L. A. Chugaev, A. A. Grinberg, K. B. Yatsimirskii, and others.

For a long period, the chemistry of complex compounds - coordination chemistry - was considered one of the sections of inorganic chemistry, since most of the known complex compounds contained inorganic molecules or ions as ligands (ammonia, water, a cyano group, etc.). The separation of coordination chemistry into an independent, intensively developing branch of chemical science is associated not only with the large number of complex compounds (complex compounds are the second most common after organic compounds, are known for almost all metal elements and for some non-metals, contain both inorganic and organic ligands of the most various types), the rapid growth in the number of objects under study and the discovery of new classes of complex compounds (organometallic compounds of the π-complex type, natural complex compounds and their synthetic analogues, etc.), but also with the development of theoretical concepts that make it possible to consider various classes of complex compounds on a single basis. The interdisciplinary position of coordination chemistry makes it necessary to use the methods of inorganic, physical, organic, analytical, and structural chemistry for its development. The study of the chemical and physicochemical properties of complex compounds contributes to the establishment of regularities that are of interest to organic, biological chemistry, catalysis, electrochemistry, photochemistry, chemical technology, materials science, medicine and other related fields.

Classification of complex compounds. The complexity of classifying complex compounds is due to their diversity. The most general principles for the classification of complex compounds are as follows: 1) by charge: neutral, for example; cationic, for example Cl 3 ; anionic, for example acidocomplexes (acid anions - acidogroups serve as ligands) - K 4 , K, etc .; cationic anionic, for example; molecular, for example Ni(CO) 4 ; 2) by type of ligands: simple, containing monodentate ligands, such as Cl 2 ; chelate - with chelate ligands attached to one central atom through two or more connecting, coordinating atoms, for example Cl 2 (en - ethylenediamine H 2 NCH 2 CH 2 NH 2 has two coordinating nitrogen atoms); containing ligands of the same type, for example Cl 3 ; containing various ligands, for example; 3) by the number of atoms of the complexing element: mononuclear (all the above examples); polynuclear (or multinuclear), for example [(en) 2 Cr(OH) 2 Cr(en) 2 ]Br 4 ; Polynuclear complex compounds also include clusters, metallocenes, complexes with bridging ligands, and some other compounds. Complexes with bridging ligands include heteropoly compounds - complex compounds of the anionic type, containing in the inner sphere as ligands anions of inorganic isopoly acids (molybdic, tungsten, etc.); isopolyanions contain M-O-M bridge bonds, where M is a complexing atom (P, As, Si, Ge, Ti, Ce), for example K 3 , K 8 .

Complex compounds with identical ligands are separated into separate groups: aqua complexes (water molecules H 2 O serve as ligands), for example [Co(H 2 O) 6 ]Cl 2 ; ammines (ligands - ammonia molecules NH 3), for example Cl 2, the same group includes ammoniates - complex compounds containing ammonia molecules not only in the inner, but also in the outer sphere; hydroxo complexes (ligands - hydroxide ions OH -), for example K 2 ; hydride complexes (ligands - hydride ions H -), for example Na, Li; halogenates (containing a halogen atom as a complexing agent and halide ligands); some other halogenates, in turn, are divided into anion halogenates, for example Rb, NH 4 (isopolyhalogenate and heteropolyhalogenate, respectively), and cationic halogenates, for example,.

The structure of complex compounds. Chemical bonds in complex compounds - a coordination bond - is carried out either by placing an unshared electron pair of a ligand donor atom on free (and accessible) electron orbitals of the central atom (acceptor), or by transferring the own electrons of the complexing metal to unfilled ligand orbitals. In the latter case, most often these are molecular antibonding π-orbitals, therefore such a bond is called π-donor, or π-dative. The most visual qualitative information about the formation of a coordination bond is given by the method of valence bonds. Detailed theoretical ideas about the structure of complex compounds are reflected in the molecular orbital method, crystal field theory, and ligand field theory. Within the framework of these approaches, explanations are given for the electronic and geometric structure of complex compounds, and estimates of the bond energies are made. In modern theories of the structure of complex compounds and the nature of the coordination bond, the concepts of Lewis acids and bases, Pearson's principle of soft and hard acids and bases are used (see the article Acids and bases).

The central atom in complex compounds can be either a metal or a non-metal. The strength of the metal-ligand coordination bond is the higher, the higher the charge of the complexing ion and the smaller its radius. The electronic structure of the central atom plays a significant role. Ions with the electronic configuration of an inert gas have the least tendency to complex formation. Stronger complexing agents are 3d-element ions, which have both incomplete and complete electron shells. Due to the larger radius and smearing of electron orbitals, ions of Ad-, 5d-, 4f-elements and especially 5f-elements form weaker bonds. These general patterns are due to the nature of the filling of the electron shell of the metal, as well as steric requirements - the optimal ratio between the sizes of the central atom and ligands. Transition metal atoms (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, rare earths, actinides). Among non-metals, B, P, and Si atoms most often act as central atoms.

Ligands in complex compounds can be anions of inorganic and organic acids (F - , Cl - , Br - , I - , CN - , NO - 2 , SO 2- 4 , PO 3- 4 , C 2 O 2- 4 , etc. ), various neutral molecules, ions and free radicals containing O, N, P, S, Se, C atoms. The activity of the ligand depends on the nature of the donor atom: hard cations (alkali, alkaline earth metals, lanthanides) are preferentially bound by the donor oxygen atom, more soft (transition d-elements) - donor atoms N, S, etc. A ligand with several donor atoms (for example, EDTA) is able to form highly stable chelate cycles. The structure (including flexibility) of the ligand molecule plays a significant role in the formation of complex compounds. According to their ability to penetrate into the electron shells of the central atom, leading to a change in its structure, ligands are conventionally divided into strong and weak field ligands.

During the formation of complex compounds, the metal-complexing agent provides its valence electron orbitals (both filled and free) to accommodate donor electron pairs of ligands. The number and direction of orbitals filled with common electrons determine the spatial structure - stereochemistry - of complex compounds. So, the sp-combination of molecular orbitals corresponds to the linear structure of complex compounds, for example +; sp 2 - flat triangular, for example (AlF 3); sp 3 - tetrahedral, for example 2+; sp 3 d - trigonal-bipyramidal, for example (NbF 5); dsp 2 - flat square, for example 2_; d 2 sp 3 or sp 3 d 2 - octahedral, for example 3+, etc. The spatial arrangement of ligands around the central atom is characterized by a coordination polyhedron.

Isomerism of complex compounds. The variety of complex compounds is due to the formation of isomers that are identical in composition, but differ in the arrangement of ligands around the central atom.

Hydrate (solvate) isomerism is due to the different distribution of water molecules and anionic ligands between the inner and outer spheres of complex compounds. For example, the compound CrCl 3 6H 2 O exists in at least three isomeric forms: Cl 3 is purple hexaaquachromium (III) trichloride, Cl 2 H 2 O is blue-green pentaaquachlorochrome (III) dichloride monohydrate and Cl 2H 2 O - tetraaquadichlorochromium (III) chloride dihydrate green. These isomers react differently with the AgNO 3 solution, since only chlorine contained in the outer sphere passes into the precipitate (AgCl).

Ionization isomerism is characterized by a different distribution of ions between the outer and inner spheres of complex compounds. When dissociated in solution, such isomers form different ions. For example, for the compound CoBrSO 4 5NH 3, two isomers are known: SO 4 - red-violet and Br - red.

Coordination isomerism consists in different distribution of ligands in internal coordination spheres. For example, the isomers and interact differently with AgNO 3: it forms a precipitate of the composition Ag 3 , leads to the precipitation of the compound Ag 3 . Geometric isomerism (cis-, trans-isomerism) is due to the different spatial arrangement of ligands around the central atom. Thus, the complex exists as a cis-isomer (formula I) and a trans-isomer (formula II), which differ from each other in a number of properties.

Optical isomerism is characterized by the ability to rotate the plane of polarization of plane polarized light. Two isomers - right and left - differ from each other in the direction of rotation. These isomers - mirror images of each other - cannot be combined in space. Of the two geometric isomers of bis-(ethylenediamine)bromochloronickel(II), only the cis-isomer can exist in the form of two optical isomers - enantiomers:

Structural (conformational) isomers are those coordination isomers in which the symmetry (spatial structure) of the coordination sphere changes.

Properties of complex compounds. There are thermodynamic stability of complex compounds - a measure of the possibility of the formation of complex compounds or its transformation into another compound under equilibrium conditions, and kinetic, which describes the rate of reactions of complexes leading to equilibrium. The thermodynamic stability of complex compounds is characterized by the terms "stable", "unstable", kinetic - "labile" and "inert". If at room temperature the reaction of the complex proceeds during the mixing of the reagents (about 1 minute), the complex compounds are classified as labile; if the reaction proceeds at a measurable rate and half the lifetime of the complex is more than 2 minutes, such complex compounds are classified as inert. For example, the rate constant of the isotope exchange of water molecules in the inner coordination sphere for the inert complex [Ni(H 2 O) 6 ] 2+ is 3.3∙10 4 s -1, for the labile [Cr(H 2 O) 6 ] 3+ - 5∙10 -7 s -1 .

The stability of complex compounds is determined by the nature of the central atom and ligand, as well as by steric factors. In accordance with the principle of hard and soft acids and bases, all central atoms are conditionally divided into hard and soft Lewis acids. Rigid Lewis acids have a small atomic or ionic radius, a high positive oxidation state, and preferentially interact with non-polarizing hard bases such as F - , OH - , NR - 2 (R - organic radical). Hard Lewis acids include ions of elements in higher oxidation states with the electronic configuration d 0 or d 10 . Soft Lewis acids have a large atomic or ionic radius and a low oxidation state, more effectively interact with easily polarizable soft ligands, such as SR 2 , PR 3 , I - , olefins. Soft Lewis acids have d-orbital electrons capable of forming π-bonds by overlapping with the vacant d-orbitals of soft ligands. The same central ions form complex compounds with olefins (like the Zeise salt). Since complex formation reactions imply the interaction of Lewis acids and bases, with an increase in the basic properties of the ligands, the stability of the complexes increases. Ligands with a higher basicity, when introduced into a solution, completely replace ligands with a lower basicity in the inner sphere.

A quantitative characteristic of the stability of complex compounds is its stability constant K = /([M][L] n), where [ML n ], [M], [L] are the equilibrium concentrations of the complex, complexing agent and ligand, respectively. To experimentally determine the stability constant, physicochemical methods are used to calculate equilibrium concentrations (pH-metric titration, conductometry, spectrophotometry, NMR spectroscopy, polarography, voltammetry, etc.).

The Gibbs free energy of the complex formation reaction ΔG 0 is related to K, the enthalpy contribution (ΔН 0) and the entropy contribution (ΔS) by the relation: -RTlnK = ΔG 0 = ΔН 0 - TΔS 0 , where T is the absolute temperature, R is the gas constant. In complex formation reactions, the enthalpy contribution is due to the difference in the total bond energy of the initial particles and the resulting complex compound; ΔH values are usually small. The entropy contribution is related to the change in the number of particles in the reaction. The loss of mobility of the metal ion and ligands when they are combined into complex compounds is usually compensated by the release of a large number of solvent (water) molecules from the solvate (hydrate) shells of the central atom and ligands. For the stability of chelate complex compounds, see the article Chelates.

Complex compounds participate in ligand addition, substitution, or elimination reactions, coordination polyhedron isomerization reactions, bound ligand reactions (eg, dissociation, ligand isomerization), and electron transfer reactions.

Methods for the synthesis of complex compounds. In a molecule of complex compounds, various metals and ligands can be combined, which makes it possible to vary the composition of complex compounds, their structure, and properties. Using an appropriate synthesis technique, it is possible to obtain complex compounds with practically any desired properties and in any state of aggregation. Numerous methods for the synthesis of complex compounds can be classified according to the types of reactions underlying them (reactions of substitution, exchange, redox, etc.). The choice of synthesis technique depends on the nature of the complex compounds (thermodynamic stability, kinetic inertness or lability) and, accordingly, is based on thermodynamic or kinetic approaches. The group of methods based on the thermodynamic approach includes reactions whose direction is determined by thermodynamic factors: the energetic advantage of the formation of the reaction product in relation to the starting compounds (negative change in the Gibbs energy). In these methods, the reaction mechanism does not play a significant role in the synthesis process. In methods based on the kinetic approach, the structure of the product is genealogically related to the starting compounds, the synthesis proceeds mainly using substitution reactions, and their mechanism plays an important role. In this case, the formation of the product can be energetically favorable, but it is also possible to obtain metastable complex compounds, the formation of which is energetically less favorable compared to other products.

A specific method for obtaining complex compounds is template synthesis, when complex organic ligands are formed during the interaction of a metal ion with simpler organic compounds. The metal ion, the matrix on which the initial ligands are fixed, contributes to the spatial orientation of the ligands and thereby determines the direction of the reaction of their interaction. In the absence of complexing metal ions, the reaction does not proceed or proceeds with a low yield. Template synthesis is most efficient for obtaining macrocyclic ligands.

Areas of application of complex compounds. Organometallic complexes are one of the most promising classes of chemical compounds on the basis of which molecular materials can be created. The combination of metal ions and organic ligands in one molecule, the possibility of purposefully changing the composition and structure of complex compounds open up opportunities for creating molecular materials based on them with a wide range of functional properties - optical, magnetic, electrical, etc. Complex compounds are used to isolate and purify platinum metals, gold, silver, nickel, cobalt, copper, in the separation of rare earth elements, alkali metals, and in a number of other technological processes. Complex compounds are used in chemical analysis for the qualitative detection and quantitative determination of many chemical elements. In living organisms, various types of complex compounds are represented by compounds of metal ions (Fe, Cu, Mg, Mn, Mo, Zn, Co) with proteins (metal proteins), vitamins, coenzymes, and other substances that perform specific functions in metabolism. Natural complex compounds are involved in the processes of respiration, photosynthesis, biological oxidation, and enzymatic processes.

Complex compounds are used in extraction and sorption processes for the separation and fine purification of rare, non-ferrous and noble metals, in analytical chemistry. Complex compounds are used as selective catalysts for various processes in the chemical and microbiological industries, for the creation of oxidants based on fluorides of halogens and noble gases, as sources of H 2 and O 2 based on hydrides and oxygen-containing compounds, in medicine, including various types of therapy. tumors, as a source of trace elements in animal husbandry and agriculture, to obtain thin coatings on various microelectronic products to impart anti-corrosion properties and mechanical strength.

Lit .: Yatsimirsky K. B. Thermochemistry of complex compounds. M., 1951; he is. Introduction to bioinorganic chemistry. K., 1976; Basolo F., Johnson R. Chemistry of coordination compounds. M., 1966; Grinberg A. A. Introduction to the chemistry of complex compounds. 4th ed. L., 1971; Day M.-K., Selbin D. Theoretical inorganic chemistry. M., 1971; Basolo F., Pearson R. Mechanisms of inorganic reactions. M., 1971; Kukushkin Yu. N. Chemistry of coordination compounds. M., 1985; he is. Reactivity of coordination compounds. L., 1987; Bersuker IB Electronic structure and properties of coordination compounds. 3rd ed. L., 1986; Housecroft K. E., Constable E. K. Modern course of general chemistry. M., 2002. T. 1-2; Kiselev Yu. M., Dobrynina NA Chemistry of coordination compounds. M., 2007.

N. A. Dobrynina, N. P. Kuzmina.

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

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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),

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Circulation 100. Order No. 73.

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 valence 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.

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(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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7. Korovin chemistry: Textbook for technical. directions and special universities-6th ed., Rev.-M.: Higher. school, 2006. S.71-82

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 valency theory. Higher-order compounds include hydrates, ammoniates, etc.

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

Werner (Switzerland) introduced into chemistry ideas about compounds of a higher order and gave them the name complex compounds. He 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 mono-, di-, etc. prefixes.

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

The names of complex compounds first indicate the anionic part in the nominative case and with the suffix -at, and then the cationic part in the genitive case. 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.

Complex compounds These are molecular or ionic compounds formed by attaching a metal or non-metal, neutral molecules or other ions to an atom or ion. They are able to exist both in a crystal and in solution.

Basic provisions and concepts of coordination theory.

To explain the structure and properties of complex compounds in 1893, the Swiss chemist A. Werner proposed a coordination theory into which he introduced two concepts: coordination and side valency.

According to Werner main valence valence is called by means of which atoms are connected to form simple compounds that obey the theory

valency. But, having exhausted the main valence, the atom is capable, as a rule, of further attachment due to side valence, as a result of the manifestation of which a complex compound is formed.

Under the influence of the forces of the main and secondary valency, atoms tend to evenly surround themselves with ions or molecules and are thus the center of attraction. Such atoms are called central or complexing agents. Ions or molecules that are directly bound to the complexing agent are called ligands.

By means of the main valency, ligands are attached to ions, and by means of secondary valency, ions and molecules are attached.

The attraction of a ligand to a complexing agent is called coordination, and the number of ligands is called the coordination number of the complexing agent.

We can say that complex compounds are compounds whose molecules consist of a central atom (or ion) directly associated with a certain number of other molecules or ions, called ligands.

Metal cations most often act as complexing agents (Co +3, Pt +4, Cr +3, Cu +2 Au +3, etc.)

The ligands can be ions Cl -, CN -, NCS -, NO 2 -, OH -, SO 4 2- and neutral molecules NH 3, H 2 O, amines, amino acids, alcohols, thioalcohols, PH 3, ethers.

The number of coordination sites occupied by the ligand near the complexing agent is called its coordination capacity or denticity.

Ligands attached to the complexing agent by one bond occupy one coordination site and are called monodentate (Cl - , CN - , NCS -). If the ligand is attached to the complexing agent through several bonds, then it is polydentate. For example: SO 4 2- , CO 3 2- are bidentate.

The complexing agent and ligands make up inner sphere compounds or complex (in the formulas, the complex is enclosed in square brackets). Ions that are not directly bound to the complexing agent are outer coordination sphere.

The ions of the outer sphere are less strongly bound than the ligands and are spatially removed from the complexing agent. They are easily replaced by other ions in aqueous solutions.

For example, in the K 3 compound, the complexing agent is Fe +2, the ligands are CN -. Two ligands are attached due to the main valence, and 4 - due to the secondary valency, therefore the coordination number is 6.

Ion Fe +2 with ligands CN - make up inner sphere or complex, and K ions + outer coordination sphere:

As a rule, the coordination number is equal to twice the charge of the metal cation, for example: singly charged cations have a coordination number equal to 2, 2-charged - 4, and 3-charged - 6. If the element exhibits a variable oxidation state, then with an increase in its coordination number increases. For some complexing agents, the coordination number is constant, for example: Co +3, Pt +4, Cr +3 have a coordination number of 6, for ions B +3, Be +2, Cu +2, Au +3 the coordination number is 4. for For most ions, the coordination number is variable and depends on the nature of the ions in the outer sphere and on the conditions for the formation of complexes.

Formed from other, simpler particles, also capable of independent existence. Sometimes complex particles are called complex chemical particles, all or part of the bonds in which are formed along.

complexing agent is the central atom of a complex particle. Typically, the complexing agent is an atom of a metal-forming element, but it can also be an atom of oxygen, nitrogen, sulfur, iodine, and other non-metal-forming elements. The complexing agent is usually positively charged and in this case is referred to in modern scientific literature metal center; the charge of the complexing agent can also be negative or equal to zero.

Ligand denticity is determined by the number of coordination sites occupied by the ligand in the coordination sphere of the complexing agent. There are monodentate (unidentate) ligands connected to the central atom through one of its atoms, that is, one covalent bond), bidentate (connected to the central atom through two of its atoms, that is, two bonds), tri-, tetradentate, etc. .

Coordination polyhedron- an imaginary molecular polyhedron, in the center of which there is a complexing atom, and in the vertices - particles of ligands directly associated with the central atom.

Tetracarbonylnickel
- dichlorodiammineplatinum(II)

According to the number of places occupied by ligands in the coordination sphere

1) Monodentate ligands. Such ligands are neutral (molecules H 2 O, NH 3, CO, NO, etc.) and charged (ions CN - , F - , Cl - , OH - , SCN - , S 2 O 3 2 - and others).

2) Bidentate ligands. Examples are ligands: aminoacetic acid ion H 2 N - CH 2 - COO - , oxalate ion - O - CO - CO - O - , carbonate ion CO 3 2 - , sulfate ion SO 4 2 - .

3) Polydentate ligands. For example, complexones are organic ligands containing in their composition several groups -C≡N or -COOH (ethylenediaminetetraacetic acid - EDTA). Cyclic complexes formed by some polydentate ligands are referred to as chelate complexes (hemoglobin, etc.).

By the nature of the ligand

1) Ammonia- complexes in which ammonia molecules serve as ligands, for example: SO 4, Cl 3, Cl 4, etc.

2) Aquacomplexes- in which water acts as a ligand: Cl 2, Cl 3, etc.

3) carbonyls- complex compounds in which the ligands are molecules of carbon monoxide (II): , .

4) acidocomplexes- complexes in which ligands are acid residues. These include complex salts: K 2 , complex acids: H 2 , H 2 .

5) Hydroxocomplexes- complex compounds in which hydroxide ions act as ligands: Na 2, Na 2, etc.

Nomenclature

1) In the name of the complex compound, the negatively charged part is indicated first - anion, then the positive part - cation.

2) The name of the complex part begins with an indication of the composition of the inner sphere. In the inner sphere, first of all, ligands are called anions, adding the ending "o" to their Latin name. For example: Cl - - chloro, CN - - cyano, SCN - - thiocyanato, NO 3 - - nitrate, SO 3 2 - - sulfito, OH - - hydroxo, etc. In this case, the terms are used: for coordinated ammonia - ammine, for water - aqua, for carbon monoxide (II) - carbonyl.

(NH 4) 2 - ammonium dihydroxotetrachloroplatinate (IV)

[Cr(H 2 O) 3 F 3] - trifluorotriaquachrome

[Сo (NH 3) 3 Cl (NO 2) 2] - dinitritechlorotriamminecobalt

Cl 2 - dichlorotetraammineplatinum(IV) chloride

NO 3 - tetraaqualitium nitrate

History

The founder of the coordination theory of complex compounds is the Swiss chemist Alfred Werner (1866-1919). Werner's 1893 coordination theory was the first attempt to explain the structure of complex compounds. This theory was proposed before the discovery of the electron by Thomson in 1896, and before the development of the electronic theory of valence. Werner did not have any instrumental research methods at his disposal, and all his research was done by interpreting simple chemical reactions.

The ideas about the possibility of the existence of "additional valences", which arose in the study of quaternary amines, Werner also applies to "complex compounds". In "On the Theory of Affinity and Valence", published in 1891, Werner defines affinity as "a force emanating from the center of the atom and spreading uniformly in all directions, the geometric expression of which is therefore not a certain number of principal directions, but spherical surface. Two years later, in the article "On the Structure of Inorganic Compounds," Werner put forward a coordination theory, according to which complex-forming atoms form the central nucleus in inorganic molecular compounds. Around these central atoms are arranged in the form of a simple geometric polyhedron a certain number of other atoms or molecules. The number of atoms grouped around the central nucleus, Werner called the coordination number. He believed that with a coordination bond there is a common pair of electrons, which one molecule or atom gives to another. Since Werner suggested the existence of compounds that no one had ever observed or synthesized, his theory was distrusted by many famous chemists, who believed that it unnecessarily complicates the understanding of chemical structure and bonds. Therefore, over the next two decades, Werner and his collaborators created new coordination compounds, the existence of which was predicted by his theory. Among the compounds they created were molecules that exhibited optical activity, that is, the ability to deflect polarized light, but did not contain carbon atoms, which were thought to be necessary for the optical activity of the molecules.

In 1911, Werner's synthesis of more than 40 optically active molecules containing no carbon atoms convinced the chemical community of the validity of his theory.

In 1913, Werner was awarded the Nobel Prize in Chemistry "in recognition of his work on the nature of the bonds of atoms in molecules, which made it possible to take a fresh look at the results of previous studies and opened up new opportunities for research work, especially in the field of inorganic chemistry ". According to Theodor Nordström, who represented him on behalf of the Royal Swedish Academy of Sciences, Werner's work "gave impetus to the development of inorganic chemistry", stimulating a revival of interest in this field after it had been neglected for some time.

Structure and stereochemistry

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.

In accordance with this theory, in complex compounds, a complexing agent, external and internal spheres are distinguished. complexing agent usually is a cation or a neutral atom. inner sphere constitutes a certain number of ions or neutral molecules that are strongly associated with the complexing agent. They are called ligands. The number of ligands determines the coordination number (CN) of the complexing agent. The inner sphere can have a positive, negative, or zero charge.

The rest of the ions that are not located in the inner sphere are located at a farther distance from the central ion, making up external coordination sphere.

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

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

Complex compounds with an outer sphere are strong electrolytes and in aqueous solutions dissociate almost completely into a complex ion and ions of the outer sphere.

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

The most typical complexing agents are cations of d-elements. Ligands can be:

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

To describe the relationship between the spatial structure of complex compounds and their physicochemical properties, representations of stereochemistry are used. The stereochemical approach is a convenient technique for representing the properties of a substance in terms of the influence of one or another fragment of the structure of a substance on the property.

The objects of stereochemistry are complex compounds, organic substances, high-molecular synthetic and natural compounds. A. Werner, one of the founders of coordination chemistry, made great efforts to develop inorganic stereochemistry. It is stereochemistry that is central in this theory, which still remains a landmark in coordination chemistry.

Isomerism of coordination compounds

There are two types of isomers:

1) compounds in which the composition of the inner sphere and the structure of the coordinated ligands are identical (geometric, optical, conformational, coordination position);

2) compounds for which differences are possible in the composition of the inner sphere and the structure of ligands (ionization, hydrate, coordination, ligand).

Spatial (geometric) isomerism

2. Orbitals with lower energy are filled first.

Given these rules, when the number of d-electrons in the complexing agent is from 1 to 3 or 8, 9, 10, they can be arranged in d-orbitals in only one way (in accordance with Hund's rule). With the number of electrons from 4 to 7 in an octahedral complex, it is possible either to occupy orbitals already filled with one electron, or to fill free dγ orbitals of higher energy. In the first case, energy is required to overcome the repulsion between electrons located in the same orbital, in the second case, to move to a higher energy orbital. The distribution of electrons in orbitals depends on the ratio between the energies of splitting (Δ) and pairing of electrons (P). At low values of Δ ("weak field"), the value of Δ can be< Р, тогда электроны займут разные орбитали, а спины их будут параллельны. При этом образуются внешнеорбитальные (высокоспиновые) комплексы, характеризующиеся определённым магнитным моментом µ. Если энергия межэлектронного отталкивания меньше, чем Δ («сильное поле»), то есть Δ >P, pairing of electrons occurs in dε orbitals and the formation of intraorbital (low spin) complexes, the magnetic moment of which µ = 0.

Application

Complex compounds are important for living organisms, so blood hemoglobin forms a complex with oxygen to deliver it to cells, chlorophyll found in plants is a complex.

Complex compounds are widely used in various industries. Chemical methods for extracting metals from ores are associated with the formation of CS. For example, to separate gold from rock, the ore is treated with a sodium cyanide solution in the presence of oxygen. The method of extracting gold from ores using cyanide solutions was proposed in 1843 by the Russian engineer P. Bagration. To obtain pure iron, nickel, cobalt, thermal decomposition of metal carbonyls is used. These compounds are volatile liquids, easily decomposing with the release of the corresponding metals.

Complex compounds have been widely used in analytical chemistry as indicators.

Many CSs have catalytic activity; therefore, they are widely used in inorganic and organic synthesis. Thus, the use of complex compounds is associated with the possibility of obtaining a variety of chemical products: varnishes, paints, metals, photographic materials, catalysts, reliable means for processing and preserving food, etc.

Complex compounds of cyanides are important in electroforming, since it is sometimes impossible to obtain such a strong coating from ordinary salt as when using complexes.

Literature

Akhmetov N. S. General and inorganic chemistry. - M.: Higher School, 2003. - 743 p.
Glinka N. L. General chemistry. - M.: Higher School, 2003. - 743 p.
Kiselev Yu. M. Chemistry of coordination compounds. - M.: Integral-Press, 2008. - 728 p.