Ligands are ions or molecules that are directly bound to the complexing agent and are donors of electron pairs. These electron-abundant systems, which have free and mobile electron pairs, can be electron donors, for example: Compounds of p-elements exhibit complexing properties and act as ligands in a complex compound. Ligands can be atoms and molecules
(protein, amino acids, nucleic acids, carbohydrates). The efficiency and strength of the donor-acceptor interaction of the ligand and the complexing agent is determined by their polarizability — the ability of the particle to transform its electron shells under external influence.
Instability constant:
Knest = 2 /
To mouth = 1 / Knest
Ligand Substitution Reactions
One of the most important stages in metal complex catalysis - the interaction of the substrate Y with the complex - occurs according to three mechanisms:
a) Replacement of the ligand with a solvent. This stage is usually depicted as the dissociation of the complex
The essence of the process in most cases is the replacement of the ligand L with a solvent S, which is then easily replaced by a substrate molecule Y
b) Attachment of a new ligand along the free coordinate with the formation of an associate followed by dissociation of the replaced ligand
c) Synchronous substitution (type S N 2) without the formation of an intermediate
Ideas about the structure of metalloenzymes and other biocomplex compounds (hemoglobin, cytochromes, cobalamins). Physicochemical principles of oxygen transport by hemoglobin.
Features of the structure of metalloenzymes.
Biocomplex compounds vary considerably in stability. The role of the metal in such complexes is highly specific: replacing it even with an element similar in properties leads to a significant or complete loss of physiological activity.
1. B12: contains 4 pyrrole rings, cobalt ion and CN- groups. Promotes the transfer of the H atom to the C atom in exchange for any group, participates in the formation of deoxyribose from ribose.
2. hemoglobin: has a quaternary structure. The four polypeptide chains are joined together to form an almost regular ball shape, where each chain contacts two chains.
Hemoglobin- a respiratory pigment that gives blood a red color. Hemoglobin is composed of protein and iron porphyrin and carries oxygen from the respiratory system to the tissues of the body and carbon dioxide from them to the respiratory organs.
Cytochromes- complex proteins (hemoproteins) that carry out a stepwise transfer of electrons and / or hydrogen from oxidized organic substances to molecular oxygen in living cells. This forms an energy-rich ATP compound.
Cobalamins- natural biologically active cobalt organic compounds. The structural basis of K. is the corrine ring, which consists of 4 pyrrole nuclei, in which nitrogen atoms are bonded to the central cobalt atom.
Physicochemical principles of oxygen transport by hemoglobin- Atom (Fe (II)) (one of the components of hemoglobin) is capable of forming 6 coordination bonds. Of these, four are used to anchor the Fe (II) atom itself in the heme, the fifth bond is used to bind the heme to the protein subunit, and the sixth bond is used to bind the O 2 or CO 2 molecule.
Metal-ligand homeostasis and the reasons for its violation. The mechanism of the toxic action of heavy metals and arsenic based on the theory of hard and soft acids and bases (HMCO). Thermodynamic principles of chelation therapy. The mechanism of the cytotoxic action of platinum compounds.
In the body, the formation and destruction of biocomplexes from metal cations and bioligands (porphins, amino acids, proteins, polynucleotides), which include donor atoms of oxygen, nitrogen, and sulfur, are continuously occurring. The exchange with the environment maintains the concentration of these substances at a constant level, providing metal- ligand homeostasis. Violation of the existing balance leads to a number of pathological phenomena - metal-excess and metal-deficient states. An example is an incomplete list of diseases associated with a change in the metal-ligand balance for only one ion - the copper cation. Deficiency of this element in the body causes Menkes syndrome, Morfan syndrome, Wilson-Konovalov disease, liver cirrhosis, pulmonary emphysema, aorto- and arteriopathy, anemia. Excessive intake of cation can lead to a series of diseases of various organs: rheumatism, bronchial asthma, inflammation of the kidneys and liver, myocardial infarction, etc., called hypercupremia. Also known professional hypercureosis - copper fever.
The circulation of heavy metals occurs partially in the form of ions or complexes with amino acids, fatty acids. However, the leading role in the transport of heavy metals belongs to proteins, which form a strong bond with them.
They are fixed on the cell membranes, block the thiol groups of membrane proteins- 50% of them are enzyme proteins that disrupt the stability of the protein-lipid complexes of the cell membrane and its permeability, causing potassium to leave the cell and the penetration of sodium and water into it.
A similar effect of these poisons, which are actively fixed on red blood cells, leads to disruption of the integrity of erythrocyte membranes, inhibition of the processes of aerobic glycolysis and metabolism in them in general, and the accumulation of hemolytically active hydrogen peroxide due to inhibition of peroxidase in particular, which leads to the development of one of the characteristic symptoms of poisoning with compounds this group - to hemolysis.
The distribution and deposition of heavy metals and arsenic occurs in almost all organs. Of particular interest is the ability of these substances to accumulate in the kidneys, which is explained by the rich content of thiol groups in the kidney tissue, the presence of a protein in it - metallobionin, which contains a large number of thiol groups, which contributes to the long-term deposition of poisons. The liver tissue, also rich in thiol groups and containing metallobionin, is also distinguished by a high degree of accumulation of toxic compounds of this group. The deposit period, for example, of mercury can be up to 2 months or more.
The release of heavy metals and arsenic occurs in different proportions through the kidneys, liver (with bile), the mucous membrane of the stomach and intestines (with feces), sweat and salivary glands, lungs, which is usually accompanied by damage to the excretory apparatus of these organs and is manifested by the corresponding clinical symptomatology.
The lethal dose for soluble mercury compounds is 0.5 g, for calomel 1–2 g, for copper sulphate 10 g, for lead acetate 50 g, for lead white 20 g, for arsenic 0.1–0.2 g.
The concentration of mercury in the blood is considered toxic more than 10 μg / L (1γ%), in urine more than 100 μg / L (10γ%), the concentration of copper in the blood is more than 1600 μg / L (160γ%), arsenic is more than 250 μg / L (25γ %) in urine.
Chelation therapy is the elimination of toxic particles
from the body, based on their chelation
complexonates of s – elements.
Drugs used for excretion
toxic substances incorporated in the body
particles are called detoxifiers.
Chapter 17 Complex Joints
17.1. Basic definitions
In this chapter, you will become familiar with a special group of complex substances called complex(or coordinating) connections.
There is currently a strict definition of the concept " complex particle " no. The following definition is commonly used.
For example, a hydrated copper ion 2 is a complex particle, since it actually exists in solutions and some crystal hydrates, is formed from Cu 2 ions and H 2 O molecules, water molecules are actually existing molecules, and Cu 2 ions exist in crystals of many copper compounds. On the contrary, the SO 4 2 ion is not a complex particle, since although O 2 ions are found in crystals, the S 6 ion does not exist in chemical systems.
Examples of other complex particles: 2, 3,, 2.
At the same time, NH 4 and H 3 O ions are referred to complex particles, although H ions do not exist in chemical systems.
Sometimes complex particles are called complex chemical particles, all or part of the bonds in which are formed by the donor-acceptor mechanism. In most complex particles it is, but, for example, in potassium alum SO 4 in the complex particle 3, the bond between the Al and O atoms is indeed formed by the donor-acceptor mechanism, and in the complex particle there is only electrostatic (ion-dipole) interaction. Confirmation of this is the existence in iron-ammonium alum of a complex particle similar in structure, in which only ion-dipole interaction is possible between water molecules and the NH 4 ion.
By charge, complex particles can be cations, anions, and also neutral molecules. Complex compounds containing such particles can belong to different classes of chemicals (acids, bases, salts). Examples: (H 3 O) - acid, OH - base, NH 4 Cl and K 3 - salts.
Usually a complexing agent is an atom of an element that forms a metal, but it can also be an atom of oxygen, nitrogen, sulfur, iodine and other elements that form non-metals. The oxidation state of the complexing agent can be positive, negative, or zero; when a complex compound is formed from simpler substances, it does not change.
Ligands can be particles that, before the formation of a complex compound, were molecules (H 2 O, CO, NH 3, etc.), anions (OH, Cl, PO 4 3, etc.), as well as a hydrogen cation. Distinguish unidentate or monodentate ligands (linked to the central atom through one of their atoms, that is, by one bond), bidentate(connected with the central atom through two of its atoms, that is, two -bonds), tridentate etc.
If the ligands are unidentate, then the coordination number is equal to the number of such ligands.
CN depends on the electronic structure of the central atom, its oxidation state, the size of the central atom and ligands, the conditions for the formation of the complex compound, temperature, and other factors. CC can take values from 2 to 12. Most often it is equal to six, somewhat less often - to four.
There are complex particles with several central atoms.
Two types of structural formulas of complex particles are used: indicating the formal charge of the central atom and ligands, or indicating the formal charge of the entire complex particle. Examples:
To characterize the shape of a complex particle, the concept of a coordination polyhedron (polyhedron) is used.
Coordination polyhedra also include a square (CN = 4), a triangle (CN = 3) and a dumbbell (CN = 2), although these figures are not polyhedra. Examples of coordination polyhedra and correspondingly shaped complex particles for the most common CN values are shown in Fig. one.
17.2. Classification of complex compounds
How chemical substances are complexed compounds are divided into ionic compounds (they are sometimes called ionogenic) and molecular ( nonionic) connections. Ionic complex compounds contain charged complex particles - ions - and are acids, bases or salts (see § 1). Molecular complex compounds consist of uncharged complex particles (molecules), for example: or - it is difficult to assign them to any main class of chemical substances.
The complex particles that make up the complex compounds are quite diverse. Therefore, for their classification, several classification features are used: the number of central atoms, the type of ligand, the coordination number, and others.
By the number of central atoms complex particles are divided into single-core and multicore... The central atoms of multinuclear complex particles can be linked to each other either directly or through ligands. In both cases, the central atoms with ligands form a single inner sphere of the complex compound:
By the type of ligands, complex particles are divided into
1) Aqua complexes, that is, complex particles in which water molecules are present as ligands. More or less stable cationic aqua complexes m, anionic aquacomplexes are unstable. All crystal hydrates refer to compounds containing aqua complexes, for example:
Mg (ClO 4) 2. 6H 2 O is actually (ClO 4) 2;
BeSO 4. 4H 2 O is actually SO 4;
Zn (BrO 3) 2. 6H 2 O is actually (BrO 3) 2;
CuSO 4. 5H 2 O is actually SO 4. H 2 O.
2) Hydroxocomplexes, that is, complex particles in which hydroxyl groups are present as ligands, which were hydroxide ions before entering the complex particle, for example: 2, 3,.
Hydroxo complexes are formed from aqua complexes exhibiting the properties of cationic acids:
2 + 4OH = 2 + 4H 2 O
3) Ammonia, that is, complex particles in which NH 3 groups are present as ligands (before the formation of a complex particle - ammonia molecule), for example: 2,, 3.
Ammoniases can also be obtained from aqua complexes, for example:
2 + 4NH 3 = 2 + 4 H 2 O
In this case, the color of the solution changes from blue to ultramarine.
4) Acidocomplexes, that is, complex particles in which acid residues of both anoxic and oxygen-containing acids are present as ligands (before the formation of a complex particle, anions, for example: Cl, Br, I, CN, S 2, NO 2, S 2 O 3 2 , CO 3 2, C 2 O 4 2, etc.).
Examples of the formation of acidocomplexes:
Hg 2 + 4I = 2
AgBr + 2S 2 O 3 2 = 3 + Br
The latter reaction is used in photography to remove unreacted silver bromide from photographic materials.
(During the development of photographic film and photographic paper, the underexposed part of the silver bromide contained in the photographic emulsion is not reduced by the developer. To remove it, this reaction is used (the process is called "fixation", since the unremoved silver bromide subsequently gradually decomposes in the light, destroying the image)
5) Complexes in which the ligands are hydrogen atoms are divided into two completely different groups: hydride complexes and complexes that are part of oniev connections.
In the formation of hydride complexes -,, -, the central atom is an electron acceptor, and a hydride ion is a donor. The oxidation state of hydrogen atoms in these complexes is –1.
In onium complexes, the central atom is an electron donor, and the acceptor is a hydrogen atom in the +1 oxidation state. Examples: H 3 O or - oxonium ion, NH 4 or - ammonium ion. In addition, there are substituted derivatives of such ions: - tetramethylammonium ion, - tetraphenylarsonium ion, - diethyloxonium ion, etc.
6) Carbonyl complexes - complexes in which CO groups are present as ligands (before the complex is formed, carbon monoxide molecules), for example:,, etc.
7) Anionhalogenate complexes - complexes of the type.
Other classes of complex particles are distinguished by the type of ligands. In addition, there are complex particles with different types of ligands; the simplest example is the aqua-hydroxocomplex.
17.3. Fundamentals of the nomenclature of complex compounds
The formula of a complex compound is composed in the same way as the formula of any ionic substance: in the first place the formula of the cation is written, in the second - the anion.
The formula of a complex particle is written in square brackets in the following sequence: in the first place is the symbol of the complexing element, then - the formulas of the ligands that were cations before the formation of the complex, then - the formulas of the ligands that were neutral molecules before the formation of the complex, and after them - the formulas of the ligands, which were anions before the formation of the complex.
The name of a complex compound is constructed in the same way as the name of any salt or base (complex acids are called hydrogen or oxonium salts). The name of the compound includes the name of the cation and the name of the anion.
The name of the complex particle includes the name of the complexing agent and the names of the ligands (the name is written in accordance with the formula, but from right to left. For complexing agents, Russian names of elements are used in cations, and Latin names in anions.
The most common ligands are:
| H 2 O - aqua | Cl - chloro | SO 4 2 - sulfato | OH - hydroxo |
| CO - carbonyl | Br - bromo | CO 3 2 - carbonato | H - hydrido |
| NH 3 - ammine | NO 2 - nitro | CN - cyano | NO - nitroso |
| NO - nitrosyl | O 2 - oxo | NCS - thiocyanato | H + I - hydro |
Examples of names for complex cations:
Examples of names for complex anions:
2 - tetrahydroxozincate ion
3 - di (thiosulfato) argentate (I) -ion
3 - hexacyanochromate (III) -ion
- tetrahydroxodiaquaaluminate ion
- tetranitrodiamminecobaltate (III) -ion
3 - pentacyanoaquaferrate (II) -ion
Examples of names for neutral complex particles:
More detailed nomenclature rules are given in reference books and special manuals.
17.4. Chemical bond in complex compounds and their structure
In crystalline complexes with charged complexes, the bond between the complex and the outer-sphere ions is ionic, and the bonds between the rest of the particles of the outer sphere are intermolecular (including hydrogen bonds). In molecular complex compounds, the bond between the complexes is intermolecular.
In most complex particles, bonds between the central atom and the ligands are covalent. All of them or part of them are formed according to the donor-acceptor mechanism (as a result, with a change in formal charges). In the least stable complexes (for example, in aqua complexes of alkaline and alkaline earth elements, as well as ammonium), ligands are held together by electrostatic attraction. A bond in complex particles is often referred to as a donor-acceptor or coordination bond.
Let us consider its formation using the example of the iron (II) aquacation. This ion is formed by the reaction:
FeCl 2cr + 6H 2 O = 2 + 2Cl
The electronic formula of the iron atom is 1 s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6. Let's make a diagram of the valence sublevels of this atom:
When a doubly charged ion is formed, the iron atom loses two 4 s-electron:
The iron ion accepts six electron pairs of oxygen atoms of six water molecules into free valence orbitals:
A complex cation is formed, the chemical structure of which can be expressed by one of the following formulas:
The spatial structure of this particle is expressed by one of the spatial formulas:
The coordination polyhedron is octahedron. All Fe-O bonds are the same. Supposed sp 3 d 2 -hybridization of the AO of the iron atom. The magnetic properties of the complex indicate the presence of unpaired electrons.
If FeCl 2 is dissolved in a solution containing cyanide ions, then the reaction proceeds
FeCl 2cr + 6CN = 4 + 2Cl.
The same complex is obtained by adding a solution of potassium cyanide KCN to the FeCl 2 solution:
2 + 6CN = 4 + 6H 2 O.
This suggests that the cyanide complex is stronger than the aqua complex. In addition, the magnetic properties of the cyanide complex indicate the absence of unpaired electrons in the iron atom. All this is due to a slightly different electronic structure of this complex:
Stronger CN ligands form stronger bonds with the iron atom, the gain in energy is enough to "break" Hund's rule and release 3 d-orbitals for lone pairs of ligands. The spatial structure of the cyanide complex is the same as that of the aqua complex, but the type of hybridization is different - d 2 sp 3 .
The "strength" of a ligand depends primarily on the electron density of the cloud of a lone pair of electrons, that is, it increases with a decrease in the size of the atom, with a decrease in the principal quantum number, depends on the type of EO hybridization and on some other factors. The most important ligands can be arranged in a row in order to increase their "strength" (a kind of "row of activity" of ligands), this row is called spectrochemical range of ligands:
| I; Br; : SCN, Cl, F, OH, H 2 O; : NCS, NH 3; SO 3 S : 2 ; : CN, CO |
For complexes 3 and 3, education schemes are as follows:
|
|
For complexes with CN = 4, two structures are possible: a tetrahedron (in the case sp 3-hybridization), for example, 2, and a flat square (in the case dsp 2 -hybridization), for example, 2.
17.5. Chemical properties of complex compounds
For complex compounds, first of all, the same properties are characteristic as for ordinary compounds of the same classes (salts, acids, bases).
If the complex compound is acid, then it is a strong acid; if the base, then the base is also strong. These properties of complex compounds are determined only by the presence of H 3 O or OH ions. In addition, complex acids, bases and salts enter into common metabolic reactions, for example:
SO 4 + BaCl 2 = BaSO 4 + Cl 2
FeCl 3 + K 4 = Fe 4 3 + 3KCl
The last of these reactions is used as a qualitative reaction for Fe 3 ions. The resulting insoluble ultramarine-colored substance is called "Prussian blue" [the systematic name is iron (III) -potassium hexacyanoferrate (II)].
In addition, the complex particle itself can enter into a reaction, and, moreover, the more active, the less stable it is. Usually these are ligand substitution reactions occurring in solution, for example:
2 + 4NH 3 = 2 + 4H 2 O,
as well as acid-base reactions like
2 + 2H 3 O = + 2H 2 O
2 + 2OH = + 2H 2 O
Formed in these reactions, after isolation and drying, turns into zinc hydroxide:
Zn (OH) 2 + 2H 2 O
The latter reaction is the simplest example of the decomposition of a complex compound. In this case, it takes place at room temperature. Other complex compounds decompose when heated, for example:
SO 4. H 2 O = CuSO 4 + 4NH 3 + H 2 O (above 300 o С)
4K 3 = 12KNO 2 + 4CoO + 4NO + 8NO 2 (above 200 o С)
K 2 = K 2 ZnO 2 + 2H 2 O (above 100 o C)
To assess the possibility of the ligand substitution reaction, the spectrochemical series can be used, guided by the fact that stronger ligands displace less strong ligands from the inner sphere.
17.6. Isomerism of complex compounds
Isomerism of complex compounds is related
1) with a possible different arrangement of ligands and outer-sphere particles,
2) with a different structure of the most complex particle.
The first group includes hydrated(in general solvate) and ionization isomerism, to the second - spatial and optical.
Hydration isomerism is associated with the possibility of different distribution of water molecules in the outer and inner spheres of the complex compound, for example: (red-brown color) and Br 2 (blue color).
Ionization isomerism is associated with the possibility of different distribution of ions in the outer and inner sphere, for example: SO 4 (purple) and Br (red). The first of these compounds forms a precipitate by reacting with a solution of barium chloride, and the second with a solution of silver nitrate.
Spatial (geometric) isomerism, otherwise called cis-trans isomerism, is characteristic of square and octahedral complexes (impossible for tetrahedral). Example: cis-trans isomerism of a square complex
Optical (mirror) isomerism in essence does not differ from optical isomerism in organic chemistry and is characteristic of tetrahedral and octahedral complexes (impossible for square ones).
One of the most important stages in metal complex catalysis - the interaction of the substrate Y with the complex - occurs according to three mechanisms:
a) Replacement of the ligand with a solvent. This stage is usually depicted as the dissociation of the complex
The essence of the process in most cases is the replacement of the ligand L with a solvent S, which is then easily replaced by a substrate molecule Y
b) Attachment of a new ligand along the free coordinate with the formation of an associate followed by dissociation of the replaced ligand
c) Synchronous substitution (type S N 2) without the formation of an intermediate
In the case of Pt (II) complexes, the reaction rate is very often described by the two-route equation
where k S and k Y- rate constants of processes proceeding by reactions (5) (with solvent) and (6) with ligand Y. For instance,
The last stage of the second route is the sum of three fast elementary stages - the cleavage of Cl -, the addition of Y, and the elimination of the H2O molecule.
In planar square complexes of transition metals, the trans effect, formulated by II Chernyaev, is observed - the effect of LT on the rate of substitution of the ligand in the trans position to the LT ligand. For Pt (II) complexes, the trans effect increases in the series of ligands:
H 2 O ~ NH 3 The presence of the kinetic trans effect and thermodynamic trans effect explains the possibility of the synthesis of inert isomeric complexes of Pt (NH 3) 2 Cl 2: Reactions of electrophilic substitution (S E) of hydrogen by a metal in the coordination sphere of a metal and processes inverse to them SH - H 2 O, ROH, RNH 2, RSH, ArH, RCCH. Even H 2 and CH 4 molecules are involved in reactions of this type Insertion reactions L by connection M-X In the case of X = R (organometallic complex), metal-coordinated molecules are also incorporated into the M-R bond (L – CO, RNC, C 2 H 2, C 2 H 4, N 2, CO 2, O 2, etc.). The insertion reactions are the result of an intramolecular attack of a nucleophile X on a molecule coordinated by the-or-type. Reverse reactions - reactions of-and-elimination Oxidative addition and reductive elimination reactions M 2 (C 2 H 2) M 2 4+ (C 2 H 2) 4– Apparently, in these reactions there is always a preliminary coordination of the attached molecule, but this is not always possible to fix. Therefore, the presence of a free site in the coordination sphere or a site associated with a solvent, which is easily replaced by a substrate, is an important factor affecting the reactivity of metal complexes. For example, bis--allyl complexes of Ni are good precursors of catalytically active particles, since a complex with a solvent appears due to the easy reductive elimination of bis-allyl, the so-called. “Bare” nickel. The role of empty seats is illustrated by the following example: Reactions of nucleophilic and electrophilic addition to - and-metal complexes As intermediates in catalytic reactions, there are both classical organometallic compounds with MC, M = C, and MC bonds, and nonclassical compounds in which the organic ligand is coordinated to the 2, 3, 4, 5, and 6 -types, or is an element of electron-deficient structures - bridging СН 3 and С 6 Н 6 -groups, non-classical carbides (Rh 6 C (CO) 16, C (AuL) 5 +, C (AuL) 6 2+, etc.). Among the specific mechanisms for classical -organometallic compounds, we note several mechanisms. Thus, 5 mechanisms of electrophilic substitution of a metal atom at the M-C bond have been established. electrophilic substitution with nucleophilic assistance AdE Attachment-Elimination AdE (C) Attachment to the C atom of bsp 2 -hybridization AdE (M) Addition oxidative to metal Nucleophilic substitution at a carbon atom in demetallation reactions of organometallic compounds occurs as a redox process: The participation of an oxidizing agent in such a stage is possible. CuCl 2, p-benzoquinone, NO 3 - and other compounds can serve as such an oxidizing agent. Here are two more elementary stages characteristic of RMX: hydrogenolysis of the M-C bond and homolysis of the M-C bond An important rule relating to all reactions of complex and organometallic compounds and associated with the principle of least motion is Tolman's 16-18 electron shell rule (Section 2). Introduction to work Relevance of work... Complexes of porphyrins with metals in high oxidation states can coordinate bases much more efficiently than complexes M 2+ and form mixed coordination compounds in which in the first coordination sphere of the central metal atom, along with the macrocyclic ligand, there are noncyclic acid ligands and sometimes coordinated molecules. The issues of ligand compatibility in such complexes are extremely important, since it is in the form of mixed complexes that porphyrins perform their biological functions. In addition, reactions of reversible addition (transfer) of base molecules, characterized by moderately high equilibrium constants, can be successfully used for the separation of mixtures of organic isomers, for quantitative analysis, for purposes of ecology and medicine. Therefore, studies of the quantitative characteristics and stoichiometry of equilibria of additional coordination on metalloporphyrins (MR) and substitution of simple ligands in them is useful not only from the point of view of theoretical knowledge of the properties of metalloporphyrins as complex compounds, but also for solving the practical problem of finding receptors and carriers of small molecules or ions. Until now, systematic studies for complexes of highly charged metal ions are practically absent. Objective... This work is devoted to the study of the reactions of mixed porphyrin-containing complexes of highly charged metal cations Zr IV, Hf IV, Mo V, and WV with bioactive N-bases: imidazole (Im), pyridine (Py), pyrazine (Pyz), benzimidazole (BzIm), characteristics stability and optical properties of molecular complexes, substantiation of stepwise reaction mechanisms. Scientific novelty... Thermodynamic characteristics were obtained for the first time by the methods of modified spectrophotometric titration, chemical kinetics, electronic and vibrational absorption and 1 H NMR spectroscopy and the stoichiometric mechanisms of reactions of N-bases with metalloporphyrins with a mixed coordination sphere (X) n-2 MTPP (X - acidoligand Cl -, OH -, O 2-, TPP - tetraphenylporphyrin dianion). It was found that in the overwhelming majority of cases the processes of formation of supramolecules metalloporphyrin - base proceed stepwise and include several reversible and slow irreversible elementary reactions of coordination of base molecules and substitution of acidoligands. For each stage of stepwise reactions, the stoichiometry, equilibrium or rate constants, orders of slow reactions with respect to the base were determined, the products were spectrally characterized (UV, visible spectra for intermediate products and UV, visible and IR - for final products). For the first time, correlation equations have been obtained that make it possible to predict the stability of supramolecular complexes with other bases. The equations were used in this work to discuss the detailed mechanism of OH - substitution in the Mo and W complexes by a base molecule. The properties of MR are described, which provide the prospect of using biologically active bases for detection, separation, and quantitative analysis, such as moderately high stability of supramolecular complexes, clear and fast optical response, low sensitivity threshold, and a second circulation time. The practical significance of the work... Quantitative results and substantiation of stoichiometric mechanisms of molecular complexation reactions are essential for the coordination chemistry of macroheterocyclic ligands. The dissertation work shows that mixed porphyrin-containing complexes exhibit high sensitivity and selectivity in relation to bioactive organic bases, within a few seconds or minutes they give an optical response suitable for the practical detection of reactions with bases - VOCs, components of drugs and food products, due to which recommended for use as components of base sensors in ecology, food industry, medicine and agriculture. Approbation of work... The results of the work were reported and discussed at: IX International conference on the problems of solvation and complexation in solutions, Ples, 2004; XII Symposium on intermolecular interactions and conformations of molecules, Pushchino, 2004; XXV, XXVI and XXIX scientific sessions of the Russian seminar on the chemistry of porphyrins and their analogues, Ivanovo, 2004 and 2006; VI School-conference of young scientists of the CIS countries on the chemistry of porphyrins and related compounds, St. Petersburg, 2005; VIII scientific school - conferences on organic chemistry, Kazan, 2005; All-Russian scientific conference "Natural macrocyclic compounds and their synthetic analogs", Syktyvkar, 2007; XVI International Conference on Chemical Thermodynamics in Russia, Suzdal, 2007; XXIII International Chugaev Conference on Coordination Chemistry, Odessa, 2007; International Conference on Porphyrins and Phtalocyanines ISPP-5, 2008; 38th International Conference on Coordination Chemistry, Israel, 2008. Reactions of substitution, addition or elimination of ligands, as a result of which the coordination sphere of the metal changes. In a broad sense, substitution reactions are understood as the processes of substitution of some ligands in the coordination sphere of a metal by others. Dissociative (D) mechanism. In the limiting case, the two-stage process proceeds through an intermediate with a lower coordination number: ML6<->+ L; + Y - "ML5Y Associative (A) mechanism. A two-stage process, characterized by the formation of an intermediate with a large coordination number: ML6 + Y =; = ML5Y + L Mutual exchange mechanism (I). Most metabolic reactions proceed by this mechanism. The process is one-step and is not accompanied by the formation of an intermediate. In the transition state, the reagent and the leaving group are bound to the reaction center, enter its nearest coordination sphere, and in the course of the reaction one group is displaced by the other, two ligands are exchanged: ML6 + Y = = ML5Y + L Internal mechanism. This mechanism characterizes the process of ligand substitution at the molecular level. 2. Features of the properties of lanthanides (Ln) associated with the effect of lanthanide compression. Ln 3+ compounds: oxides, hydroxides, salts. Other oxidation states. Examples of the reducing properties of Sm 2+, Eu 2+ and the oxidizing properties of Ce 4+, Pr 4+. The monotonic decrease in atomic and ionic radii when moving along a series of 4f-elements is called lanthanide compression. I am. It leads to the fact that the radii of the atoms of the 5d transition elements of the fourth (hafnium) and fifth (tantalum) groups following the lanthanides are practically equal to the radii of their electronic analogs from the fifth period: zirconium and niobium, respectively, and the chemistry of heavy 4d and 5d metals has a lot in common. Another consequence of f-compression is the closeness of the ionic radius of yttrium to the radii of heavy f-elements: dysprosium, holmium, and erbium. All REEs form stable oxides in the +3 oxidation state. They are refractory crystalline powders that slowly absorb carbon dioxide and water vapor. Oxides of most elements are obtained by calcining hydroxides, carbonates, nitrates, oxalates in air at a temperature of 800-1000 ° C. Form oxides M2O3 and hydroxides M (OH) 3 Scandium Hydroxide Amphoterine Only Oxides and hydroxides dissolve easily in acids Sc2O3 + 6HNO3 = 2Sc (NO3) 3 + 3H2O Y (OH) 3 + 3HCl = YCl3 + 3H2O Only scandium compounds are hydrolyzed in aqueous solution Cl3 ⇔ Cl2 + HCl All halides are known in the +3 oxidation state. All are refractory. Fluorides are poorly soluble in water. Y (NO3) 3 + 3NaF = YF3 ↓ + 3NaNO3
Coordinated ligand reactions
Reactions of organometallic compounds
