How to determine the oxidation state. Determination of the oxidation state of compounds
First, let's try to understand what this term represents. The oxidation state according to the periodic table represents the number of electrons that are accepted or given up by an element in the process of chemical interaction. It can take on a negative and positive value.
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Linking to a table
How is the oxidation state determined? The periodic table consists of eight groups arranged vertically. Each of them has two subgroups: main and secondary. In order to set metrics for elements, you must use certain rules.
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Instructions
How to calculate the oxidation states of elements? The table allows you to fully cope with this problem. Alkali metals, which are located in the first group (main subgroup), exhibit an oxidation state in compounds, it corresponds to +, equal to their highest valency. Metals of the second group (subgroup A) have a +2 oxidation state.
The table allows you to determine this value not only for elements exhibiting metallic properties, but also for non-metals. Their maximum value will correspond to the highest valency. For example, for sulfur it will be +6, for nitrogen +5. How is their minimum (lowest) figure calculated? The table answers this question as well. You need to subtract the group number from eight. For example, for oxygen it will be -2, for nitrogen -3.
For simple substances that have not entered into chemical interaction with other substances, the determined indicator is considered equal to zero.
Let's try to identify the main actions related to arrangement in binary compounds. How to set the oxidation state in them? The periodic table helps solve the problem.
For example, let's take calcium oxide CaO. For calcium, located in the main subgroup of the second group, the value will be constant, equal to +2. For oxygen, which has non-metallic properties, this indicator will be a negative value, and it corresponds to -2. In order to check the correctness of the definition, we summarize the obtained figures. As a result, we get zero, therefore, the calculations are correct.
Let us determine similar indicators in another binary compound CuO. Since copper is located in a secondary subgroup (first group), therefore, the studied indicator may exhibit different values. Therefore, to determine it, you must first identify the indicator for oxygen.
The nonmetal located at the end of the binary formula has a negative oxidation number. Since this element is located in the sixth group, when subtracting six from eight, we obtain that the oxidation state of oxygen corresponds to -2. Since there are no indices in the compound, therefore, the oxidation state index of copper will be positive, equal to +2.
How else is a chemistry table used? The oxidation states of elements in formulas consisting of three elements are also calculated using a specific algorithm. First, these indicators are placed at the first and last element. For the first, this indicator will have a positive value, corresponding to valence.
For the outermost element, which is a non-metal, this indicator has a negative value; it is determined as a difference (the group number is subtracted from eight). When calculating the oxidation state of a central element, a mathematical equation is used. When calculating, the indices available for each element are taken into account.
The sum of all oxidation states must be zero.
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Example of determination in sulfuric acid
The formula of this compound is H2SO4. Hydrogen has an oxidation state of +1, and oxygen has an oxidation state of -2. To determine the oxidation state of sulfur, we create a mathematical equation: + 1 * 2 + X + 4 * (-2) = 0. We find that the oxidation state of sulfur corresponds to +6.
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Conclusion
Using the rules, you can assign coefficients in redox reactions. This issue is discussed in the ninth grade chemistry course of the school curriculum. In addition, information about oxidation states allows you to complete OGE and USE tasks.
OXIDATION DEGREES OF CHEMICAL ELEMENTS.
We already know about the existence of charged ion particles. The positive charge of an ion is equal to the number of electrons given up by one atom of the element; the negative charge of an ion is equal to the number of electrons accepted by one atom of the element.
The entries Na+, Ca2+, Al3+ mean that the atoms of these elements have lost 1, 2, 3 e-, respectively, and the entries F-, O2-, N3- mean that the atoms of these elements have gained 1, 2, and 3e-, respectively. Oxidation states of elements. To determine the composition of molecular compounds (SO2, NH3, CO2, etc.) and ionic simple compounds (Na2O, Na2SO4, etc.).
When assessing the oxidation state of elements, compounds are represented as split into monoatomic ions. The oxidation number is the nominal charge of the atoms of a chemical element in a compound, calculated from the assumption that the compounds consist only of ions.
Oxidation states can have a positive, negative or zero value, and the sign is placed before the number: -1, -2, +3, in contrast to the charge of the ion, where the sign is placed after the number.
r/>In molecules, the algebraic sum of the oxidation states of elements, taking into account the number of their atoms, is equal to 0. The oxidation states of metals in compounds are always positive, the highest oxidation state corresponds to the number of the group of the periodic system where the element is located (excluding some elements: gold Au+3 (I group), Cu+2 (II), from group VIII the oxidation state +8 can only be found in osmium Os and ruthenium Ru. The degrees of non-metals can be both positive and negative, depending on which atom it is connected to: if with an atom metal is always negative, if with a non-metal there can be both + and - (you will learn about this when studying a number of electronegativity).The highest negative oxidation state of non-metals can be found by subtracting from 8 the number of the group in which the element is located, the highest positive equal to the number of electrons in the outer layer (the number of electrons corresponds to the group number).The oxidation states of simple substances are equal to 0, regardless of whether it is a metal or a non-metal.
When determining oxidation states, the following rules must be used:
Source: https://znaivse.biz/obrazovanie/kak-opredelit-stepen-okisleniya-20-01-2020.html
How to determine the oxidation state: periodic table and algorithm of actions:
How to determine the oxidation state? The periodic table allows you to record this quantitative value for any chemical element.
Definition
First, let's try to understand what this term represents. The oxidation state according to the periodic table represents the number of electrons that are accepted or given up by an element in the process of chemical interaction. It can take on a negative and positive value.
Conclusion
Using the rules, you can assign coefficients in redox reactions. This issue is discussed in the ninth grade chemistry course of the school curriculum. In addition, information about oxidation states allows you to complete OGE and USE tasks.
Source: https://www.syl.ru/article/287818/new_kak-opredelit-stepen-okisleniya-tablitsa-mendeleeva-i-algoritm-deystviy
Copper - chemical properties
Copper is located in group 11 of the Periodic Table of Chemical Elements D.I. Mendeleev.
In the fourth period, copper is the penultimate d-element, its valence electrons are 3 d94 s2, however, due to the stability the d10 state, the transition of one d-electron to the 4s sublevel is more energetically favorable, therefore the valence electrons of copper have the following configuration: 3 d104 s1 . In copper compounds, the characteristic oxidation state is +2; oxidation states +1 and +3 are possible.
Physical properties of copper
Copper is a ductile, pinkish-red metal with a metallic sheen. It has high thermal and electrical conductivity; its electrical conductivity is second only to silver. Melting point 1083°C, boiling point 2567°C, density 8.92 g/cm3.
In air, copper is covered with a dense green-gray film of basic carbonate, which protects it from further oxidation.
Chemical properties of copper
With oxygen, depending on the temperature of interaction, copper forms two oxides:
2Cu + O2 = 2CuO (black)
At a temperature of about 150 °C, the metal is covered with a dark red film of copper (I) oxide:
4Cu + O2 = 2Cu2O
When heated with fluorine, chlorine, bromine, copper (II) halides are formed:
Cu + Br2 = CuBr2;
with iodine – copper (I) iodide is formed:
2Cu + I2 = 2CuI.
Cu + S = CuS
4Cu + SO2= Cu2S + 2CuO
4Cu + 2NO2 = 4CuO + N2
Interaction with acids
In the electrochemical voltage series of metals, copper is located after hydrogen, so it does not interact with solutions of dilute hydrochloric and sulfuric acids and alkalis.
Dissolves in dilute nitric acid to form copper(II) nitrate and nitric oxide:
3Cu + 8HNO3 = 3Cu(NO3)2 + 2NO + 4H2O.
Reacts with concentrated solutions of sulfuric and nitric acids to form copper (II) salts and acid reduction products:
Cu + 2H2SO4 = CuSO4 + SO2 + 2H2O;
Cu + 4HNO3 = Cu(NO3)2 + 2NO2 + 2H2O.
Copper reacts with concentrated hydrochloric acid to form hydrogen trichlorocuprate (II):
Cu + 3HCl = H[CuCl3] + H2
Source: http://himege.ru/med-ximicheskie-svojstva/
Oxidation states - what is this value? How to determine the oxidation state of elements?
Such a school curriculum subject as chemistry causes numerous difficulties for most modern schoolchildren; few can determine the degree of oxidation in compounds. The greatest difficulties are experienced by schoolchildren who study inorganic chemistry, that is, primary school students (grades 8-9). Misunderstanding of the subject leads to the emergence of hostility among schoolchildren towards this subject.
Teachers identify a number of reasons for this “dislike” of middle and high school students for chemistry: reluctance to understand complex chemical terms, inability to use algorithms to consider a specific process, problems with mathematical knowledge. The Ministry of Education of the Russian Federation has made serious changes to the content of the subject. In addition, the number of hours for teaching chemistry was also “cut.” This had a negative impact on the quality of knowledge in the subject and decreased interest in studying the discipline.
What chemistry course topics are most difficult for schoolchildren?
According to the new program, the course of the basic school discipline “Chemistry” includes several serious topics: D.I. Mendeleev’s periodic table of elements, classes of inorganic substances, ion exchange. The most difficult thing for eighth graders is determining the degree of oxidation of oxides.
Arrangement rules
First of all, students should know that oxides are complex two-element compounds that include oxygen. A prerequisite for a binary compound to belong to the class of oxides is the location of oxygen second in this compound.
It will be possible to calculate such an indicator in any formulas of this class only if the student knows a certain algorithm.
Algorithm for acid oxides
To begin with, we note that oxidation states are numerical expressions of the valence of elements. Acidic oxides are formed by non-metals or metals with a valence of four to seven, the second in such oxides is always oxygen.
In oxides, the valence of oxygen always corresponds to two; it can be determined from the periodic table of elements by D.I. Mendeleev.
A typical nonmetal like oxygen, being in group 6 of the main subgroup of the periodic table, accepts two electrons to completely complete its outer energy level.
Nonmetals in compounds with oxygen most often exhibit a higher valence, which corresponds to the number of the group itself. It is important to remember that the oxidation state of chemical elements is an indicator that assumes a positive (negative) number.
The nonmetal at the beginning of the formula has a positive oxidation state. The nonmetal oxygen in oxides is stable, its index is -2. In order to check the reliability of the arrangement of values in acid oxides, you will have to multiply all the numbers you entered by the indices of a specific element. Calculations are considered reliable if the total sum of all the pros and cons of the given degrees is 0.
Compiling two-element formulas
The oxidation state of the atoms of elements gives the chance to create and write compounds from two elements. When creating a formula, firstly, both symbols are written side by side, and oxygen is always placed second.
Above each of the recorded signs, the values of the oxidation states are written down, then between the found numbers there is a number that will be divisible by both numbers without any remainder.
This indicator must be divided separately by the numerical value of the oxidation state, obtaining indices for the first and second components of the two-element substance. The highest oxidation state is numerically equal to the value of the highest valence of a typical non-metal and is identical to the number of the group where the non-metal is located in the PS.
Algorithm for setting numerical values in basic oxides
Oxides of typical metals are considered such compounds. In all compounds they have an oxidation state index of no more than +1 or +2. In order to understand what oxidation state a metal will have, you can use the periodic table. For metals of the main subgroups of the first group, this parameter is always constant, it is similar to the group number, that is, +1.
The metals of the main subgroup of the second group are also characterized by a stable oxidation state, in digital terms +2. The oxidation states of oxides in total, taking into account their indices (numbers), should give zero, since the chemical molecule is considered a neutral particle, devoid of charge.
Arrangement of oxidation states in oxygen-containing acids
Acids are complex substances consisting of one or more hydrogen atoms that are bonded to some kind of acidic moiety. Given that oxidation states are numbers, calculating them will require some math skills. This indicator for hydrogen (proton) in acids is always stable and is +1. Next, you can indicate the oxidation state for the negative oxygen ion; it is also stable, -2.
Only after these steps can the oxidation state of the central component of the formula be calculated. As a specific example, consider determining the oxidation state of elements in sulfuric acid H2SO4. Considering that the molecule of this complex substance contains two hydrogen protons and 4 oxygen atoms, we obtain an expression of the form +2+X-8=0. In order for the sum to form zero, sulfur will have an oxidation state of +6
Arrangement of oxidation states in salts
Salts are complex compounds consisting of metal ions and one or more acidic residues. The method for determining the oxidation states of each of the constituent parts in a complex salt is the same as in oxygen-containing acids. Considering that the oxidation state of elements is a digital indicator, it is important to correctly indicate the oxidation state of the metal.
If the metal forming the salt is located in the main subgroup, its oxidation state will be stable, corresponds to the group number, and is a positive value.
If the salt contains a metal of a similar PS subgroup, exhibiting different valences, the valence of the metal can be determined by the acid residue.
After the oxidation state of the metal has been established, set the oxidation state of oxygen (-2), then calculate the oxidation state of the central element using a chemical equation.
As an example, consider the determination of oxidation states of elements in sodium nitrate (average salt). NaNO3. The salt is formed by a metal of the main subgroup of group 1, therefore, the oxidation state of sodium will be +1. Oxygen in nitrates has an oxidation state of -2. To determine the numerical value of the oxidation state, the equation is +1+X-6=0. Solving this equation, we find that X should be +5, this is the oxidation state of nitrogen.
Basic terms in OVR
There are special terms for the oxidation and reduction processes that schoolchildren must learn.
The oxidation state of an atom is its direct ability to attach to itself (donate to others) electrons from some ions or atoms.
An oxidizing agent is considered to be neutral atoms or charged ions that gain electrons during a chemical reaction.
The reducing agent will be uncharged atoms or charged ions that lose their own electrons in the process of chemical interaction.
Oxidation is thought of as a procedure of donating electrons.
Reduction involves the acceptance of additional electrons by an uncharged atom or ion.
The redox process is characterized by a reaction during which the oxidation state of an atom necessarily changes. This definition provides insight into how one can determine whether a reaction is ODD.
Rules for parsing OVR
Using this algorithm, you can arrange the coefficients in any chemical reaction.
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First you need to arrange the oxidation states of each chemical substance. Please note that in a simple substance the oxidation state is zero, since there is no recoil (addition) of negative particles. The rules for arranging oxidation states in binary and three-element substances were discussed above.
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Then you need to determine those atoms or ions whose oxidation states changed during the transformation.
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From the left side of the written equation, atoms or charged ions are isolated that have changed their oxidation states. This is necessary to create a balance sheet. Their values must be indicated above the elements.
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Next, those atoms or ions that were formed during the reaction are written down, indicated by the sign + the number of electrons accepted by the atom, - the number of negative particles given up. If after the interaction process the oxidation states decrease. This means that electrons have been accepted by the atom (ion). As the oxidation state increases, an atom (ion) gives up electrons during the reaction.
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The smallest total number is divided first by the electrons received, then by the electrons given up in the process, and the coefficients are obtained. The numbers found will be the desired stereochemical coefficients.
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The oxidizing agent, the reducing agent, and the processes occurring during the reaction are determined.
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The last step will be the arrangement of stereochemical coefficients in the reaction under consideration.
OVR example
Let's consider the practical application of this algorithm on a specific chemical reaction.
Fe+CuSO4=Cu+FeSO4
We calculate the indicators for all simple and complex substances.
Since Fe and Cu are simple substances, their oxidation state is 0. In CuSO4, then Cu+2, then oxygen has 2, and sulfur has +6. In FeSO4: Fe +2, therefore, for O-2, according to calculations S +6.
Now we are looking for elements that could change the indicators, in our situation they will be Fe and Cu.
Since after the reaction the value of the iron atom became +2, 2 electrons were given up in the reaction. Copper changed its indicators from +2 to 0, therefore, copper accepted 2 electrons. Now we determine the number of electrons accepted and given up by the iron atom and the divalent copper cation. During the transformation, two electrons are taken by the divalent copper cation, and the same number of electrons are given up by the iron atom.
In this process, there is no point in determining the minimum common multiple, since an equal number of electrons are accepted and donated during the transformation. Stereochemical coefficients will also correspond to unity. In the reaction, iron will exhibit the properties of a reducing agent, and it will oxidize. The divalent copper cation is reduced to pure copper, in the reaction it has the highest oxidation state.
Application of processes
The formulas for the oxidation state should be known to every student in grades 8-9, since this question is included in the OGE tasks. Any processes that occur with oxidative and reduction characteristics play an important role in our lives. Without them, metabolic processes in the human body are impossible.
Source: https://FB.ru/article/241628/stepeni-okisleniya---eto-kakaya-velichina-kak-opredelit-stepen-okisleniya-elementov/amp
Zhuravleva T. | Complex connections | Journal "Chemistry" No. 6/2005
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 BaSO4 will immediately form.
Research has established that the dark blue color of an ammonia solution is due to the presence in it of complex ions [Cu(NH3)4]2+, formed by adding four ammonia molecules to a copper ion. When water evaporates, [Cu(NH3)4]2+ ions bind to ions, and dark blue crystals are released from the solution, the composition of which is expressed by the formula [Cu(NH3)4]SO4•H2O.
Comprehensive
are compounds 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
Reactants Complex compounds Complex ions| CuSO4 + 4NH3 | [Cu(NH3)4]SO4 | [Cu(NH3)4]2+ |
| Fe(CN)2 + 4KCN | K4[Fe(CN)6] | [Fe(CN)6]4– |
| PtCl2 + 2NH3 | [Pt(NH3)2Cl2] | – |
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, complex compounds are divided into complexing agents , outer and inner spheres . 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 the coordination number (CN) of the complexing agent.
Example of a complex compound
The compound [Cu(H2O)4)]SO4•H2O or CuSO4•5H2O considered in the example is a crystalline hydrate of copper(II) sulfate.
Let's determine the components of other complex compounds, for example K4[Fe(CN)6].
(Reference: A substance with the formula HCN is hydrocyanic acid. Salts of hydrocyanic acid are called cyanides.)
The complexing agent is the iron ion Fe2+, 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, a bond can be formed between the central atom and the ligands according to 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 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 outer sphere ions. For example:
[Cu(NH3)4]SO4 [Cu(NH3)4]2+ + .
During exchange reactions, complex ions move from one compound to another without changing their composition:
[Cu(NH3)4]SO4 + BaCl2 = [Cu(NH3)4]Cl2 + BaSO4.
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, [Pt(NH3)2Cl2].
The most typical complexing agents are cations of d -elements.
Ligands
can be:
a) polar molecules – NH3, H2O, CO, NO;
b) simple ions – F–, Cl–, Br–, I–, H–, H+;
c) complex ions – CN–, SCN–, NO2–, OH–.
Let's consider a table that shows the coordination numbers of some complexing agents.
Table
Coordination
Jonah number
| 2 | Cu+, Ag+, Au+ |
| 4 | Cu2+, Hg2+, Sn2+, Pt2+, Pb2+, Ni2+, Co2+, Zn2+, Au3+, Al3+ |
| 6 | Fe2+, Fe3+, Co2+, Co3+, Ni2+, Cr3+, Sn4+, Pt4+ |
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 named, adding the suffix - o- , for example: Cl– – chloro, CN– – cyano, OH– – hydroxo, etc.
Next, neutral ligands are called, primarily ammonia and its derivatives. In this case, the following terms are used: for coordinated ammonia - ammine , for water - aqua . The number of ligands is indicated in Greek words: 1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa. Then they move on to the name of the central atom.
If the central atom is part of the cations, then use the Russian name of the corresponding element and indicate its oxidation state in parentheses (in Roman numerals). If the central atom is contained in an anion, then use the Latin name of the element, and 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 the complex [Cu(NH3)4]Сl2, determine the oxidation state (С.О.) x of the complexing agent – the Cu x + ion:
1• x + 2•(–1) = 0, x = +2,CO(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:
[Cu(NH3)4]Cl2 – tetraammine copper(II) chloride,
[Co(NH3)3H2OCl2]NO3 – dichloroaquatriammine cobalt(III) nitrate,
K3[Fe(CN)6] – potassium hexacyanoferrate(III),
K2[PtCl4] – potassium tetrachloroplatinate(II),
[Zn(NH3)4Cl2] – dichlorotetraamminzinc,
H2[SnCl6] – 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.
K4[Fe(CN)6] – potassium hexacyanoferrate(II),
K4[Fe(CN)6] 4K+ + [Fe(CN)6]4–.
H[AuCl4] – tetrachloroauric acid (formed when gold is dissolved in aqua regia),
H[AuCl4] H+ + [AuCl4]–.
[Ag(NH3)2]OH – diammine silver(I) hydroxide (this substance is involved in the “silver mirror” reaction),
[Ag(NH3)2]OH [Ag(NH3)2]+ + OH–.
Na[Al(OH)4] – sodium tetrahydroxoaluminate,
Na[Al(OH)4] Na+ + [Al(OH)4]–.
Complex compounds also include many organic substances, in particular, the known products of the interaction of amines with water and acids. For example, the salts methyl ammonium chloride 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, 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.
Source: https://him.1sept.ru/article.php?id=200500610
