Complex connections

Lecture lesson notes

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

DURING THE CLASSES

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

What happened? Chemical reaction? Until now, we didn't know that ammonia could react with salt. What substance was formed? What is its formula, structure, name? What class of compounds does it belong to? Can ammonia react with other salts? Are there connections similar to this? We have to answer these questions today.

To better study the properties of some compounds of iron, copper, silver, aluminum, we need knowledge about complex compounds.

Let's continue our experience. Divide the resulting solution into two parts. Add lye to one part. Precipitation of copper(II) hydroxide Cu(OH) 2 is not observed, therefore, there are no doubly charged copper ions in the solution or there are too few of them. From this we can conclude that copper ions interact with the added ammonia and form some new ions that do not form an insoluble compound with OH – ions.

At the same time, the ions remain unchanged. This can be verified by adding a solution of barium chloride to the ammonia solution. A white precipitate of BaSO 4 will immediately form.

Research has established that the dark blue color of an ammonia solution is due to the presence in it of complex 2+ ions, formed by the addition of four ammonia molecules to the copper ion. When water evaporates, 2+ ions bind to ions, and dark blue crystals are released from the solution, the composition of which is expressed by the formula SO 4 H 2 O.

Complex compounds are those containing complex ions and molecules capable of existing both in crystalline form and in solutions.

The formulas of molecules or ions of complex compounds are usually enclosed in square brackets. Complex compounds are obtained from ordinary (non-complex) compounds.

Examples of obtaining complex compounds

The structure of complex compounds is considered on the basis of the coordination theory proposed in 1893 by the Swiss chemist Alfred Werner, Nobel Prize winner. His scientific activity took place at the University of Zurich. The scientist synthesized many new complex compounds, systematized previously known and newly obtained complex compounds, and developed experimental methods for proving their structure.

A. Werner (1866–1919)

In accordance with this theory, complex compounds are distinguished complexing agent, external And inner sphere. The complexing agent is usually a cation or neutral atom. The inner sphere consists of a certain number of ions or neutral molecules that are tightly bound to the complexing agent. They are called ligands. The number of ligands determines coordination number(CN) complexing agent.

Example of a complex compound

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

Let's determine the components of other complex compounds, for example K 4.
(Reference. A substance with the formula HCN is hydrocyanic acid. Salts of hydrocyanic acid are called cyanides.)

The complexing agent is the iron ion Fe 2+, the ligands are cyanide ions CN –, the coordination number is six. Everything written in square brackets is the inner sphere. Potassium ions form the outer sphere of the complex compound.

The nature of the bond between the central ion (atom) and the ligands can be twofold. On the one hand, the connection is due to the forces of electrostatic attraction. On the other hand, between the central atom and the ligands a bond can be formed by a donor-acceptor mechanism, similar to the ammonium ion. In many complex compounds, the bond between the central ion (atom) and the ligands is due to both the forces of electrostatic attraction and the bond formed due to the lone electron pairs of the complexing agent and the free orbitals of the ligands.

Complex compounds with an outer sphere are strong electrolytes and in aqueous solutions dissociate almost completely into the complex ion and ions external sphere. For example:

SO 4 2+ + .

During exchange reactions, complex ions move from one compound to another without changing their composition:

SO 4 + BaCl 2 = Cl 2 + BaSO 4.

The inner sphere can have a positive, negative or zero charge.

If the charge of the ligands compensates for the charge of the complexing agent, then such complex compounds are called neutral or non-electrolyte complexes: they consist only of the complexing agent and inner sphere ligands.

Such a neutral complex is, for example, .

The most typical complexing agents are cations d-elements.

Ligands can be:

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

Let's consider a table that shows the coordination numbers of some complexing agents.

Nomenclature of complex compounds. The anion in a compound is called first and then the cation. When indicating the composition of the inner sphere, the anions are first called, adding the suffix - to the Latin name. O-, for example: Cl – – chloro, CN – – cyano, OH – – hydroxo, etc. Hereinafter referred to as neutral ligands and primarily ammonia and its derivatives. In this case, the following terms are used: for coordinated ammonia - ammin, for water – aqua. The number of ligands is indicated in Greek words: 1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa. Then they move on to the name of the central atom. If the central atom is part of the cations, then use Russian name of the corresponding element and indicate its oxidation state in parentheses (in Roman numerals). If the central atom is contained in the anion, then use Latin name element, and at the end they add the ending - at. In the case of non-electrolytes, the oxidation state of the central atom is not given, because it is uniquely determined from the condition of electrical neutrality of the complex.

Examples. To name a complex Cl 2, determine the oxidation state (S.O.)
X complexing agent – ​​Cu ion X+ :

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

The oxidation state of the cobalt ion is determined similarly:

y + 2 (–1) + (–1) = 0,y = +3, S.O.(Co) = +3.

What is the coordination number of cobalt in this compound? How many molecules and ions surround the central ion? The coordination number of cobalt is six.

The name of a complex ion is written in one word. The oxidation state of the central atom is indicated by a Roman numeral placed in parentheses. For example:

Cl 2 – tetraammine copper(II) chloride,
NO 3 – dichloroaquatriammine cobalt(III) nitrate,
K 3 – hexacyanoferrate(III) potassium,
K 2 – tetrachloroplatinate(II) potassium,
– dichlorotetraamminzinc,
H 2 – hexachlorotanic acid.

Using the example of several complex compounds, we will determine the structure of molecules (complexing ion, its SO, coordination number, ligands, inner and outer spheres), give a name to the complex, and write down the equations of electrolytic dissociation.

K 4 – potassium hexacyanoferrate(II),

K 4 4K + + 4– .

H – tetrachlorauric acid (formed when gold is dissolved in aqua regia),

H H + + –.

OH – diamminesilver(I) hydroxide (this substance participates in the “silver mirror” reaction),

OH + + OH – .

Na – tetrahydroxoaluminate sodium,

Na Na + + – .

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

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

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

Complex compounds are widely used:

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

II.1. Concept and definition.

Complex compounds are the most numerous class of inorganic compounds. It is difficult to give a brief and comprehensive definition of these compounds. Complex compounds are also called coordination compounds. The chemistry of coordination compounds intertwines organic and inorganic chemistry.

Until the end of the 19th century, the study of complex compounds was purely descriptive. 1893 Swiss chemist Alfred Werner created the coordination theory. Its essence is as follows: in complex compounds there is a regular geometric arrangement of atoms or groups of atoms, called ligands or addends, around a central atom - the complexing agent.

Thus, complex chemistry studies ions and molecules consisting of a central particle and ligands coordinated around it. The central particle, a complexing agent, and ligands directly associated with it form the inner sphere of the complex. For inorganic ligands, most often, their number coincides with the coordination number of the central particle. Thus, the coordination number is the total number of neutral molecules or ions (ligands) associated with the central atom in the complex

Ions located outside the inner sphere form the outer sphere of the complex compound. In formulas, the inner sphere is enclosed in square brackets.

K 4 4- - inner sphere or complex ion

complexing ion coordination

The complexing agents are:

1) positive metal ions (usually d-elements): Ag +, Fe 2+, Fe 3+, Cu 2+, Al 3+, Co 3+; etc. (complexing ions).

2) less often - neutral metal atoms related to d-elements: (Co, Fe, Mn, etc.)

3) some non-metal atoms with different positive oxidation states - B +3, Si +4, P +5, etc.

Ligands can be:

1) negatively charged ions (OH - , Hal - , CN - cyano group, SCN - thiocyano group, NH 2 - amino group, etc.)

2) polar molecules: H 2 O (ligand name is “aqua”), NH 3 (“ammin”),

CO (“carbonyl”).

Thus, complex compounds (coordination compounds) are complex chemical compounds that contain complex ions formed by a central atom in a certain oxidation state (or with a certain valency) and associated ligands.

II.2. Classification

I. By the nature of the ligands:

1. Aqua complexes (H 2 O)

2. Hydroxo complexes (OH)

3. Amine complexes (NH 3) - ammonia

4. Acid complexes (with acidic residues - Cl -, SCN -, S 2 O 3 2- and others)

5. Carbonyl complexes (CO)

6. Complexes with organic ligands (NH 2 -CH 2 -CH 2 -NH 2, etc.)

7. Anion halides (Na)

8. Amino complexes (NH 2)

II. According to the charge of the complex ion:

1. Cationic type - the charge of the complex ion is positive

2. Anion type - the charge of the complex ion is negative.

To correctly write a complex compound, it is necessary to know the oxidation state of the central atom, its coordination number, the nature of the ligands and the charge of the complex ion.

II.3. The coordination number can be defined as the number of σ bonds between neutral molecules or ions (ligands) and the central atom in the complex.

The value of the coordination number is determined mainly by the size, charge and structure of the electron shell of the complexing agent. The most common coordination number is 6. It is typical for the following ions: Fe 2+, Fe 3+, Co 3+, Ni 3+, Pt 4+, Al 3+, Cr 3+, Mn 2+, Sn 4+.

K3, Na3, Cl3

hexacyanoferrate (III) hexanitrocobaltate (III) hexaaquachrome (III) chloride

potassium sodium

Coordination number 4 is found in 2-charged ions and in aluminum or gold: Hg 2+, Cu 2+, Pb 2+, Pt 2+, Au 3+, Al 3+.

(OH) 2 - tetraammine copper(II) hydroxide;

Na 2 – sodium tetrahydroxocuprate (II)

K 2 – potassium tetraiodomercurate (II);

H – hydrogen tetrachloroaurate(III).

Often the coordination number is defined as twice the oxidation state of the complexing ion: for Hg 2+, Cu 2+, Pb 2+ - the coordination number is 4; Ag +, Cu + - have a coordination number of 2.

To determine whether the objects are located in the internal or external sphere, it is necessary to carry out qualitative reactions. For example, potassium K 3 -hexacyanoferrate(III). It is known that the iron ion (+3) forms dark red iron thiocyanate (+3) with the thiocyanate anion.

Fe 3+ +3 NH 4 SCN à Fe (SCN) 3 + 3NH 4 +

When a solution of ammonium or potassium thiocyanate is added to a solution of potassium hexacyanoferrate(III), no color is observed. This indicates the absence of iron ions Fe 3+ in the solution in sufficient quantities. The central atom is connected to the ligands by a covalent polar bond (donor-acceptor mechanism of bond formation), so the ion exchange reaction does not occur. On the contrary, the outer and inner spheres are connected by an ionic bond.

II.4. The structure of a complex ion from the point of view of the electronic structure of the complexing agent.

Let us analyze the structure of the tetraammine copper (II) cation:

a) electronic formula of the copper atom:

2 8 18 1 ↓ ↓ ↓ ↓ ↓

b) electronic formula of the Cu 2+ cation:

Cu 2+)))) ↓ ↓ ↓ ↓ 4p 0

4s o:NH 3:NH 3: NH 3: NH 3

CuSO 4 + 4: NH 3 -à SO 4

SO 4 à 2+ + SO 4 2-

ionic bond

cov. connection

according to the donor-acceptor mechanism.

Exercise for independent solution:

Draw the structure of complex ion 3- using the algorithm:

a) write the electronic formula of the iron atom;

b) write the electronic formula of the iron ion Fe 3+, removing electrons from the 4s sublevel and 1 electron from the 3d sublevel;

c) rewrite the electronic formula of the ion again, transferring the electrons of the 3d sublevel to an excited state by pairing them in the cells of this sublevel

d) count the number of all free cells on 3d, 4s, 4p - sublevels

e) place the cyanide anions CN - under them and draw arrows from the ions to the empty cells.

II.5. Determination of the charge of the complexing agent and complex ion:

1. The charge of the complex ion is equal to the charge of the outer sphere with the opposite sign; he also equal to the sum charge of the complexing agent and all ligands.

K 2 +2+ (- 1) 4 =x x = -2

2. The charge of the complexing agent is equal to the algebraic sum of the charges of the ligands and the outer sphere (with the opposite sign).

Cl x +0·2 +(–1)·2 = 0; x=2-1= +1

SO 4 x+ 4 0 -2 = 0 x = +2

3. The higher the charge of the central atom and the lower the charge of the ligand, the higher the coordination number.

II.6. Nomenclature.

There are several ways to name complex compounds. Let's choose a simpler one using the valence (or oxidation state) of the central atom

II.6.1. Name of complex compounds of cationic type:

Complex compounds are of the cationic type if the charge of the complex ion is positive.

When naming complex compounds:

1) first the coordination number is called using Greek prefixes (hexa, penta, three);

2) then, charged ligands with the addition of the ending “o”;

3) then, neutral ligands (without the ending “o”);

4) complexing agent in Russian in genitive case, its valence or oxidation state is indicated and then called an anion. Ammonia - the ligand is called "ammine" without the "o", water - "aqua"

SO 4 tetraammine copper (II) sulfate;

Cl diammine silver (I) chloride;

Cl 3 – hexaiodocobalt (III) chloride;

Cl – oxalatopentaaqua-aluminium(III) chloride

(okalate is a doubly charged anion of oxalic acid);

Cl 3 – hexaaquatic iron(III) chloride.

II.6.2. Nomenclature of complex compounds of anionic type.

The cation, coordination number, ligands and then the complexing agent - the central atom - are named. The complexing agent is called Latin in the nominative case with the ending “at”.

K 3 – potassium hexafluoroferrate(III);

Na 3 – sodium hexanitrocobaltate (III);

NH 4 – ammonium dithiocyanodicarbonyl mercuryate (I)

Neutral complex: – iron pentacarbonyl.

EXAMPLES AND TASKS FOR INDEPENDENT SOLUTION

Example 1. Classify, fully characterize and give names to the following complex compounds: a) K 3 –; b) Cl; V) .

Solution and answer:

1) K 3 - 3 ions K + - outer sphere, its total charge is +3, 3- - inner sphere, its total charge is equal to the charge of the outer sphere, taken with the opposite sign - (3-)

2) A complex compound of anionic type, since the charge of the inner sphere is negative;

3) The central atom is a complexing agent - silver ion Ag +

4) Ligands - two doubly charged thiosulfuric acid residues H 2 S 2 O 3, belongs to acido complexes

5) The coordination number of the complexing agent in this case, as an exception, is 4 (two acid residues have 4 valence σ bonds without 4 hydrogen cations);

6) The charge of the complexing agent is +1:

K 3 : +1 3 + X + (-2) 2 = 0 à X= +1

7) Name: – potassium dithiosulfate argentate (I).

1) Cl - 1 ion - Cl - - outer sphere, its total charge is -1, - - inner sphere, its total charge is equal to the charge of the outer sphere, taken with the opposite sign - (3+)

2) A complex compound of the cationic type, since the charge of the inner sphere is positive.

3) The central atom is a complexing agent - cobalt ion Co, calculate its charge:

: X + 0 4 + (-1) 2 = +1 à X = 0 +2 +1 = +3

4) Complex connection mixed type, since it contains different ligands; acid complex (Cl - hydrochloric acid residue) and ammin complex - ammonia (NH 3 - ammonia-neutral compound)

6) Name – dichlorotetraammine cobalt(III) chloride.

1) - there is no external sphere

2) A complex compound of neutral type, since the charge of the inner sphere = 0.

3) The central atom is a complexing agent - a tungsten atom,

its charge =0

4) Carbonyl complex, since the ligand is a neutral particle - carbonyl - CO;

5) The coordination number of the complexing agent is 6;

6) Name: – hexacarbonyl tungsten

Task 1. Characterize complex compounds:

a) Li 3 Cr (OH) 6 ]

b) I 2

c) [Pt Cl 2 (NH 3) 2 ] and give them names.

Task 2. Name the complex compounds: NO 3,

K 3, Na 3, H, Fe 3 [Cr (CN) 6] 2

Chemistry test - complex compounds - URGENT! and got the best answer

Answer from Nick[guru]
Some questions were asked incorrectly, for example 7,12,27. Therefore, the answers contain caveats.
1. What is the coordination number of the complexing agent in the +2 complex ion?
AT 6
2. What is the coordination number of the complexing agent in the complex ion 2+?
B) 6
3. What is the coordination number of the complexing agent in the complex ion 2+
B) 4
4. What is the coordination number of Cu²+ in the complex ion +?
B) 4
5. What is the coordination number of the complexing agent in the complex ion: +4?
B) 6
6. Determine the charge of the central ion in the complex compound K4
B) +2
7. What is the charge of a complex ion?
B) +2 – if we assume that the complexing agent is Cu (II)
8. Among the iron salts, identify the complex salt:
A) K3
9. What is the coordination number of Pt4+ in the complex 2+ ion?
A) 4
10. Determine the charge of the complex ion K2?
B) +2
11. Which molecule corresponds to the name tetraammine copper (II) dichloride?
B) Cl2
12. What is the charge of a complex ion?
D) +3 – if we assume that the complexing agent is Cr (III)
13. Among copper (II) salts, determine the complex salt:
B) K2
14. What is the coordination number of Co3+ in the complex ion +?
B) 6
15. Determine the charge of the complexing agent in complex compound K3?
D) +3
16. Which molecule corresponds to the name potassium tetraiodohydrate (II)?
A) K2
17. What is the charge of a complex ion?
AT 2
18. Among nickel (II) salts, identify the complex salt:
B) SO4
19. What is the coordination number of Fe3+ in the complex ion -3?
AT 6
20. Determine the charge of the complexing agent in complex compound K3?
B) +3
21. Which molecule corresponds to the name silver diamine chloride (I)?
B) Cl
22. What is the charge of the K4 complex ion?
B) -4
23. Among the zinc salts, identify the complex salt
B) Na2
24. What is the coordination number of Pd4+ in the 4+ complex ion?
D) 6
25. Determine the charge of the complexing agent in the complex compound H2?
B) +2
26. Which molecule corresponds to the name potassium hexacyanoferrate (II)?
D) K4
27. What is the charge of a complex ion?
D) -2 – if we assume that the complexing agent is Co (II)
27. Among chromium (III) compounds, identify the complex compound
B) [Cr (H2O) 2(NH3)4]Cl3
28. What is the coordination number of cobalt (III) in the NO3 complex ion?
B) 6
29. Determine the charge of the complexing agent in the complex compound Cl2
A) +3
30. Which molecule corresponds to the name sodium tetraiodopalladate (II)?
D) Na2

Answer from James Bond[newbie]
Oh my God

Answer from Kitten...[guru]
No. 30 last

Today I worked on this lit review. If it is useful to someone, I will be glad. If someone doesn't understand, it's okay.

Ammonia are complex compounds in which the functions of ligands are performed by ammonia molecules NH 3 . A more precise name for complexes containing ammonia in the internal sphere is ammines; however, NH 3 molecules can be located not only in the inner, but also in the outer sphere of the ammonia compound.

Ammonium salts and ammonia compounds are usually considered as two types of complex compounds similar in composition and many properties, the first - ammonia with acids, the second - ammonia with salts mainly heavy metals.

Ammonia complexes are usually obtained by reacting metal salts or hydroxides with ammonia in aqueous or non-aqueous solutions, or by treating the same salts in a crystalline state ammonia gas: For example, the ammonia complex of copper is formed as a result of the reaction:

Cu 2+ + 4NH 3 → 2+

The chemical bond between ammonia molecules and the complexing agent is established through a nitrogen atom, which serves as a donor lone pair of electrons.

The formation of amino complexes in aqueous solutions occurs through sequential replacement of water molecules in the internal sphere of aqua complexes to ammonia molecules:

2+ + NH 3 . H2O2+ + 2 H 2 O;

2+ + NH 3 . H2O2+ + 2H 2 O

We should not forget about the interaction of ammonia with the salt anion. The reaction of formation of copper tetraammonate from copper sulfate and an aqueous ammonia solution looks like this:

CuSO 4 + 2NH 3 + 2H 2 O = Cu(OH) 2 + (NH 4) 2 SO 4

Cu(OH) 2 + 4NH 3 = (OH) 2

Another name for the resulting compound is Schweitzer's reagent; in its pure form, it is an explosive compound, often used as a cellulose solvent and in the production of copper-ammonium fibers.

The most stable among ammonia complexes:

3+ (b 6 = 1.6 . 10 35),

-[Cu(NH 3) 4 ] 2+ (b 4 = 7.9 . 10 12),

2+ (b 4 = 4.2. 10 9) and some others.

Ammonia is destroyed by any influence that removes (by heating) or destroys (by the action of an oxidizing agent) the molecule ammonia, convert ammonia in an acidic environment into an ammonium cation (the ammonium cation does not contain lone pairs of electrons and therefore cannot act as a ligand), or bind the central atom complex, for example, in the form of a slightly soluble precipitate:

Cl 2 = NiCl 2 + 6 NH 3 ( G)

SO 4 + 6 Br 2 = CuSO 4 + 12 HBr + 2 N 2 ( G)

SO 4 + 3 H 2 SO 4 = NiSO 4 + 3 (NH 4) 2 SO 4

(OH)2 + Na2S + 4H2O = CuS¯ + 2 NaOH + 4 NH 3 . H2O (4)

Ammonias differ both in composition + , 2+ and in stability in aqueous solutions; they are used in analytical chemistry for detection and separation of metal ions.

When heated (depending on pressure - from 80 to 140 ºС) and reduced pressure, copper ammonia can lose ammonia and pass from the form of tetraammonium to diammonium, as shown by the example of copper nitrate ammonia in experimental work (2).

With more intense chemical decomposition, copper nitrate can decompose to water, nitrogen and copper. Table 1 shows the comparative characteristics of tetraamicate copper nitrate and ammonium nitrate.

Table 1: Comparative characteristics tetraammonium nitrate copper and ammonium nitrate (3)

Substance	Formula	Density (g/cm e)	Heat of formation (cal/mol)	Decomposition reaction equation	Heat of decomposition reaction		Gas volume (l/kg)
					kcal/mol	kcal/kg
Ammonium nitrate	NH4NO3	1,73	87.3	2H 2 O vapor +N 2 +1/2O 2
Copper nitrate tetraammonium oxide	[Cu(NH3) 4 ] (N0 3) 2			6H2O+3N 2 +Cu l

The significantly greater (1.6–1.7 times per unit weight) heat of thermal decomposition of copper nitrate tetraammonium oxide compared to NH 4 N0 3 suggests that combustion or explosion reactions can be initiated in them relatively easily. In 1964, Preller (4) studied the sensitivity and some explosive properties of copper (II, cobalt (III) and nickel (II) ammonias. It turned out that these compounds have significant explosive properties and their detonation speed is 2400 —3500 m/sec.

The researchers also studied combustion copper nitrate tetraammonium nitrate. The flash point of this compound was 288ºС at a heating rate of 20 degrees/min. The ability of copper ammonia to burn at high blood pressure(not less than 60 atm.). This fact once again confirms the position put forward, according to which any chemical system in which an exothermic reaction can occur chemical reaction, when selecting appropriate conditions, should be capable of propagating a combustion reaction in it.

Copper (II) present in tetrammine can be reduced to (I) to produce monovalent copper diammonicate. An example of such a reaction is the interaction of blue copper tetraammonate with copper shavings at room temperature, slight stirring and no interaction with air. During the reaction, the blue color disappears.

(OH) 2 + Cu = 2(OH)

Cuprous diammonate easily oxidizes to tetrammine when interacting with atmospheric oxygen.

4(OH) + 2H2O + O2 + 8NH3 = 4(OH)2

Conclusion: This kind of work should have been done a long time ago. A huge layer of knowledge on ammonia compounds of heavy metals, in particular copper, has been touched upon, which may be worth studying further in addition to our developments and research.

A striking example of this is the dissertation of SERGEEVAALEXANDRA ALEXANDROVNA on the topic: « INFLUENCE OF AMMONIATES ON PHOTOSYNTHESIS, PRODUCTIVITY OF AGRICULTURAL CROPS AND EFFICIENCY OF FERTILIZER USE” where the benefits of using heavy metal ammonia as a fertilizer to improve the productivity and photosynthesis of plants are thoroughly proven.

List of used literature:

1. Materials from the site http://ru.wikipedia.org
2. Copper (II) nitrate ammonias Cu(NH3)4(NO3)2 and Cu(NH3)2(NO3)2. Thermolysis under reduced pressure. S.S. Dyukarev, I.V. Morozov, L.N. Reshetova, O.V. Guz, I.V. Arkhangelsky, Yu.M. Korenev, F.M. Spiridonov. Journal of Inorg.Chem. 1999
3. Zh 9, 1968 UDC 542.4: 541.49 STUDY OF THE COMBUSTION ABILITY OF COPPER AND COBALT NITRATE AMMONIACATES A. A. Shidlovsky and V. V. Gorbunov
4. N. R g e 11 e g, Explosivsto "f., 12, 8, 173 (1964)
5. Materials from the site http://www.alhimik.ru. Toolkit for students (MITHT)
6. Masterials from the site http://chemistry-chemists.com

Chapter 17. Complex connections

17.1. Basic definitions

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

Currently, a strict definition of the concept " complex particle" No. The following definition is usually used.

For example, a hydrated copper ion 2 is a complex particle, since it actually exists in solutions and some crystalline hydrates, it is formed from Cu 2 ions and H 2 O molecules, water molecules are real 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 occur 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 classified as complex particles, although H ions do not exist in chemical systems.

Sometimes complex chemical particles are called complex particles, all or part of the bonds in which are formed according to the donor-acceptor mechanism. In most complex particles this is the case, but, for example, in potassium alum SO 4 in complex particle 3, the bond between the Al and O atoms is actually formed according to the donor-acceptor mechanism, and in the complex particle there is only an electrostatic (ion-dipole) interaction. This is confirmed by the existence in iron-ammonium alum of a complex particle similar in structure, in which only ion-dipole interaction is possible between water molecules and the NH 4 ion.

Based on their charge, complex particles can be cations, anions, or neutral molecules. Complex compounds containing such particles can belong to different classes of chemical substances (acids, bases, salts). Examples: (H 3 O) is an acid, OH is a base, NH 4 Cl and K 3 are salts.

Typically the complexing agent is an atom of the element that forms the metal, but it can also be an atom of oxygen, nitrogen, sulfur, iodine, and other elements that form nonmetals. 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 (connected to the central atom through one of their atoms, that is, by one -bond), bidentate(connected to the central atom through two of their atoms, that is, by two -bonds), tridentate etc.

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

The 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. CN can take values ​​from 2 to 12. Most often it is six, somewhat less often – 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 complex particles with corresponding shapes for the most common CN values ​​are shown in Fig. 1.

17.2. Classification of complex compounds

As chemical substances, complex compounds are divided into ionic compounds (they are sometimes called ionic) 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 - classifying them into any main class of chemical substances is difficult.

The complex particles included in complex compounds are quite diverse. Therefore, several classification features are used to classify them: the number of central atoms, the type of ligand, the coordination number and others.

According to the number of central atoms complex particles are divided into single-core And multi-core. The central atoms of multinuclear complex particles can be connected to each other either directly or through ligands. In both cases, the central atoms with ligands form a single internal sphere of the complex compound:

Based on the type of ligands, complex particles are divided into

1) Aqua complexes, that is, complex particles in which water molecules are present as ligands. Cationic aqua complexes m are more or less stable, anionic aqua complexes are unstable. All crystal hydrates belong 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;
CuSO4. 5H 2 O is actually SO 4. H2O.

2) Hydroxo complexes, that is, complex particles in which hydroxyl groups are present as ligands, which were hydroxide ions before entering the composition of the complex particle, for example: 2, 3, .

Hydroxo complexes are formed from aqua complexes that exhibit 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 molecules), for example: 2, , 3.

Ammonia can also be obtained from aquatic complexes, for example:

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

The color of the solution in this case changes from blue to ultramarine.

4) Acid complexes, that is, complex particles in which acid residues of both oxygen-free 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 acid complexes:

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.
(When developing photographic film and photographic paper, the unexposed 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 “fixing”, since the unremoved silver bromide gradually decomposes in the light, destroying the image)

5) Complexes in which hydrogen atoms are the ligands are divided into two completely different groups: hydride complexes and complexes included in the composition onium connections.

During the formation of hydride complexes – , , – the central atom is an electron acceptor, and the donor is the hydride ion. 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 formation of the complex - molecules of carbon monoxide), for example: , , etc.

7) Anion halogenates complexes – complexes of type .

Based on the type of ligands, other classes of complex particles are also distinguished. In addition, there are complex particles with different types of ligands; The simplest example is aqua-hydroxo complex.

17.3. Basics of complex compound nomenclature

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

The formula of a complex particle is written in square brackets in the following sequence: the symbol of the complex-forming element is placed first, 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, the Russian names of the elements are used in cations, and Latin ones in anions.

Names of the most common ligands:

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 of complex cations:

Examples of names of complex anions:

2 – tetrahydroxozincate ion
3 – di(thiosulfato)argentate(I) ion
3 – hexacyanochromate(III) ion
– tetrahydroxodiaquaaluminate ion
– tetranitrodiammine cobaltate(III) ion
3 – pentacyanoaquaferrate(II) ion

Examples of names of neutral complex particles:

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

17.4. Chemical bonds in complex compounds and their structure

In crystalline complex compounds with charged complexes, the bond between the complex and the outer-sphere ions is ionic, the bonds between the remaining particles of the outer sphere are intermolecular (including hydrogen). In molecular complex compounds, the connection between the complexes is intermolecular.

In most complex particles, the 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 consequence - with a change in formal charges). In the least stable complexes (for example, in aqua complexes of alkali and alkaline earth elements, as well as ammonium), the ligands are held by electrostatic attraction. Bonding in complex particles is often called donor-acceptor or coordination bonding.

Let us consider its formation using the example of iron(II) aquacation. This ion is formed by the reaction:

FeCl 2cr + 6H 2 O = 2 + 2Cl

Electronic formula of the iron atom is 1 s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6. Let's draw up 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 shape of the coordination polyhedron is octahedron. All Fe-O bonds are the same. Supposed sp 3 d 2 - AO hybridization 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 occurs

FeCl 2cr + 6CN = 4 + 2Cl.

The same complex is obtained by adding a solution of potassium cyanide KCN to a solution of FeCl 2:

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 the 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 the ligand depends primarily on the electron density of the cloud of lone pairs of electrons, that is, it increases with decreasing atomic size, with decreasing principal quantum number, depends on the type of EO hybridization and on some other factors. The most important ligands can be arranged in a series of increasing “strength” (a kind of “activity series” of ligands), this series is called spectrochemical series of ligands:

I ; Br ; : SCN, Cl, F, OH, H2O; : NCS, NH 3; SO 3 S : 2 ; : CN, CO

For complexes 3 and 3, the formation schemes are as follows:

For complexes with CN = 4, two structures are possible: 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

Complex compounds are primarily characterized by the same properties as ordinary compounds of the same classes (salts, acids, bases).

If the complex compound is an acid, then it is a strong acid; if it is a base, then it is a strong base. 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 ordinary exchange 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 qualitative reaction to Fe 3 ions. The resulting ultramarine-colored insoluble substance is called “Prussian blue” [systematic name: iron(III)-potassium hexacyanoferrate(II).

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

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

as well as acid-base reactions such as

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

The product formed in these reactions, after isolation and drying, turns into zinc hydroxide:

Zn(OH) 2 + 2H 2 O

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

SO4. H 2 O = CuSO 4 + 4NH 3 + H 2 O (above 300 o C)
4K 3 = 12KNO 2 + 4CoO + 4NO + 8NO 2 (above 200 o C)
K 2 = K 2 ZnO 2 + 2H 2 O (above 100 o C)

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

17.6. Isomerism of complex compounds

Isomerism of complex compounds is associated
1) with possible different arrangements of ligands and outer-sphere particles,
2) with a different structure of the complex particle itself.

The first group includes hydrate(in general solvate) And ionization isomerism, to the second - spatial And optical.

Hydrate isomerism is associated with the possibility of different distribution of water molecules in the outer and inner spheres of a complex compound, for example: (red-brown color) and Br 2 (blue color).

Ionization isomerism is associated with the possibility of different distributions of ions in the outer and inner spheres, 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 ones). Example: cis-trans isomerism of a square complex

Optical (mirror) isomerism is essentially no different from optical isomerism in organic chemistry and is characteristic of tetrahedral and octahedral complexes (impossible for square ones).