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Coordination chemistry

Branch of Chemistry

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Coordination chemistry is the study of the interaction between metal atoms or ions and inorganic, organic ions or molecules Coordination compound And their bonding, structure, reaction, classification and preparation.

Chinese name: Coordination chemistry

Foreign name: coordination chemistry
Formation: Coordination compound

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brief introduction

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Earliest recorded Complex It was used as pigment in the early 18th century prussian blue K〔FeⅡ（CN）6FeⅢ〕。 In 1798, CoCl3 · 6NH3 was found to be a stable compound formed by CoCl3 and NH3, and the research on its composition and properties created the field of coordination chemistry. In 1893, Switzerland Chemist A Werner First, the correct chemical formula and coordination theory of such compounds are proposed Coordination compound The concept of side valence was introduced in, and it was proposed that elements have side valence in addition to the main valence, thus explaining the existence of coordination compounds and their dissociation 。

stay Coordination compound Medium, Central atom And Ligands Between Coordination bond Combination. The theories that explain coordination bonds are Valence bond theory 、 Crystal field theory and Molecular orbital theory 。

Coordination chemistry and organic, analytical and other chemical fields biochemistry 、 Pharmaceutical chemistry 、 chemical industry It is closely related and widely used: ① Extraction and separation of metals. Separating metals from ores for further purification, such as solvents extraction , ion exchange, etc Complex Is related to the generation of. ② Coordination catalysis 。 Transition metal compounds can olefin 、 Alkyne And carbon monoxide and other unsaturated molecules Coordination compound And activate these molecules to form new compounds. Therefore, these coordination compounds are catalysts for the reaction. ③ chemical analysis 。 Coordination reaction stay Gravimetric analysis 、 Capacity analysis 、 Spectrophotometric analysis It is widely used in Chromogenic agent 、 indicator 、 Precipitant 、 Titrant 、 Extractant 、 Masking agent , which can increase the sensitivity of analysis and reduce the separation steps. ④ biochemistry. Many organisms metallic element All with Complex Exists in the form of, for example hemoglobin Is an iron complex; Chlorophyll is a magnesium complex; Vitamin B12 It is a cobalt complex. ⑤ Medical Science. available EDTA disodium salt It forms a complex with mercury Harmful element Excretion. Cis dichloro diammonium platinum (Ⅱ) has been proved to be an anticancer drug.

brief history

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The earliest recorded Complex It was used as pigment in the early 18th century prussian blue , the chemical formula is KFe [Fe (CN) 6]. CoCl3 · 6 discovered in 1798 NH3 。 CoCl3 and NH3 are both stable compounds. After they are combined into new compounds, their properties are different from those of component compounds. This discovery initiated the study of coordination chemistry.

More cobalt ammonia complexes and other complexes were discovered in the 19th century. 1893 Switzerland Chemist A. Werner first proposed the correct chemical formula and Coordination theory 。 He introduced the concept of side valence in complexes and proposed that elements have side valence in addition to the main valence. For example, in a series of platinum (Ⅳ) complexes, the main valence of platinum is+4 and the side valence is+6, which can explain the existence and dissociation (Table 1). The number of ions generated is determined by the solution conductivity and Free chlorine Determination of ions by analysis. because Werner In 1913 Nobel Prize in Chemistry 。

Coordination bond

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explain Coordination bond There are three theories of Valence bond theory 、 Crystal field theory and Molecular orbital theory 。

Valence bond theory

Mainly by L C. Pauling developed it. This theory believes that Complex Is on Lewis base （ ligand ）And Lewis acid (metal or metal ion) acid-base theory ）, between ligand and metal Coordination bond Generation (not all coordination keys). Ligands Electron pair Go to Metal Hybridization Atomic orbital On.

Crystal field theory

It is considered that metal - ligand The key is created by Point charge The reaction between the ligands is generated, and the ligands are regarded as point charges or dipole , thus affecting d occupied by metal ions Orbital energy And used to describe its bonding structure.

Molecular orbital theory

Think that electrons surround the whole Complex Systematic molecular orbital Sports, it integrates Valence bond and Crystal field theory , is currently the most widely used theory.

stability

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With metal ions and ligand of because Complex The generation of positive electricity Metal ions and ligands of anion or Dipolar molecule Metallic ion Ionic potential （ cation The larger the ratio of charge to its radius, the more stable the complexes with the same ligand will be. Stability of complexes It is also associated with the ligand anion Polarizability of Within a certain limit, the greater the polarizability of anions, the easier the ligands become electrons Donor 。 For example, for the fourth cycle from Mn reach Zn The stability of its complex is based on F< OS >P order changes. For precious metals with d or d structure, the stability of their complexes changes in the order of P>S ≥ N>O>F ≥ Cl<Br<I.

The stability of the complex is also affected Chelation That is, ligands with more than two teeth are connected with metal ions in more than one position to form a ring. Generally, when the degree of chelation increases, Complex The stability of, for example ethylenediamine The stability of the complex is better than Ammonia complex Large.

type

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Press Central atom Classification has single core Complex and Polynuclear complex ； Press ligand Classification, common ones are hydration Complexes, halogenated complexes Ammonia complex , cyanide complex, metal carbonyl Compounds, etc; According to the type of bonding, there are classical complexes (σ - bonding) and cluster complexes (metal - Metal bond ）、 olefin Isounsaturated ligand complexes (π- σ bond And π - π Feedback key ）, ferrocene and other sandwich, cave and cage complexes（ Delocalization Conjugate coordination), etc; There are inorganic complexes Organometallic compound , Biology inorganic compound Etc. There are overlaps between various classifications.

Hydrated complex

abbreviation hydrate 。 by metal ion And water Molecularly formed Complex 。 Almost all metal ions can form hydrated complexes in aqueous solutions, such as【 Cu ( H2O ）4】 And【 Cr (H2O) 6], common coordination number It's 4 and 6. When other ligand When added to the aqueous solution of metal ions, water displacement occurs and other complexes are formed. In these Displacement reaction In general, the coordination number of metal remains unchanged. But this is not always the case, for example, adding CN ions to an aqueous solution containing [Ni (H2O) 6], and finally generating [Ni (CN) 4] and [Ni (CN) 5]; take Cl Ions added to [Fe (H2O) 6] can produce [FeCl4], etc.

Halogenated complex

Metal ions and halogen (fluorine, chlorine, bromine, iodine) ion Complex 。 Most metal ions can form halide complexes, such as K2 [PtCl4] and Na3 [AlF6]. Halogenation Stability of complexes There is a wide range of changes. Press Soft and hard acid-base theory The concept of ligand Classification. Metal ions are divided into hard acid and Soft acid 。 Hard acid refers to those metal ions with small volume, high charge and no valence shell electrons that are easy to deform or move, such as Be Mg , Al, Sc, La, Cr, Co, Fe, etc; Soft acid refers to those metal ions with large volume, low charge and valence shell electrons that are easy to deform or move, such as Cu, Ag Au 、Cd、Hg、 Pd And Pt, etc. Ligands can also be classified into non polarizable Hard alkali And polarizable Soft alkali F and Cl in halogen are hard alkali, I is soft alkali, and Br is between them. Hard acid is easy to combine with hard base, and soft acid is easy to combine with soft base.

Halogenation of Hard Acids Complex The stability in aqueous solution increases in the order of I ＜ Br ＜ Cl ≤ F, and the stability of metal halide complexes of soft acids increases in the order of F ≤ Cl ＜ Br ＜ I.

Metal carbonyl compound

For metal and carbon monoxide Combined products. In metal carbonyl Metallic Oxidized state Both are very low. Some carbonyl compounds have zero metal oxidation state, such as Ni（ CO ）4； Some are in negative oxidation state, such as Na [Co (CO) 4]; Some are in normal oxidation state, such as [Mn (CO) 5Br]. These are mononuclear carbonyl compounds. There are also polynuclear metal carbonyl compounds, such as Fe2 (CO) 9 and Fe3 (CO) 12 (see Carbonyl metal ）。

Cluster complex

That is, cluster compounds. Containing at least two metals and containing metals- Metal bond Of Complex , such as Fe3 (CO) 12, Co4 (C5H5) 4H4, (W6Cl12) Cl6, etc. The metals that can form cluster compounds are mainly transition metal (See Transitional element ）, their formation trend is similar to that of the metal in periodic table Position, oxidation state and ligand Property. Generally speaking, the Elemental formation The ability of cluster complexes is worse than that of the corresponding second and third transition system elements. stay Homogeneous element The low oxidation state is easy to form cluster complexes (see Cluster metal compound ）。

Organometallic compound

Or called Organometallic compound For the generation of carbon between organic groups and metals Metal bond Compounds. many Organometallic compound Often with Complex There are two types of such complexes: ① metal and carbon Bonding σ bond of (see covalent bond ）Organometallic compounds, including alkyl Metal [such as (CH3) 6Al2], aryl metal (such as C6H5HgCl), ethynyl metal (such as HC 呏 C-Ag) and other compounds. Most of these compounds, except organic ligand In addition, it can also contain other ligands, such as CO, CN, PR3 (R is alkyl), etc.; ② pi bond Organometallic compounds, including olefin 、 Alkyne 、 aromatic hydrocarbon 、 Cyclopentadiene Base and other complexes, such as Chase salt K【PtCl2( C2H4 ）】, its structure is as follows. At Pt and CH2 =There are π - σ and π - π bonds between CH2. Later, olefins of silver, copper, palladium, ruthenium and other metal ions were successively produced Complex 。 Another example Ferrocene (C5H5) 2Fe (see Structural a）， Metal atoms are sandwiched between two parallel carbon ring systems, called Sandwich compound 。 except Cyclopentadiene Besides the base, there are other unsaturated rings ligand Sandwich compounds such as Diphenylchromium (C6H5)2Cr(b)。 Elements that generate sandwich compounds, mainly Transitional element Group IV to VII elements in and Group VIII elements other than platinum, and Lanthanide and Actinide element (See Bond type of organometallic compounds ）。

Bioinorganic compounds Biological ligands and metallic Complex 。 Although they are not abundant in organisms Organism Of Life activities It plays an important role in. Multi metal protein yes Metalloenzyme , can often catalyze certain reactions, such as zinc containing carbonic anhydrase Catalyzable carbon dioxide Hydration reaction Or its Reverse reaction ； Ferritin （ myoglobin 、 hemoglobin and Earthworm hemoglobin ）, including Copper protein (blood penicillium) and vanadium containing protein（ Blood Vanadium Protein ）It can store and deliver oxygen. Other important bio inorganic complexes are chlorophyll 、 Vitamin B12 Etc. (see Bioinorganic Chemistry ）。

Preparation method

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many Complex It can be obtained by direct addition of its constituent compounds, such as gas phase BF3 And NH3 to prepare [F3B · NH3].

By a ligand Replacing another ligand is also a commonly used method for preparing complexes. For example, use ethylenediamine Replacement [Co（ NO2 ）6】 And give cis - [Co (en) 2 (NO2) 2] (en is ethylenediamine).

When metal ions have different oxidation states Redox reaction Different preparations Valence state Metal complexes. Highly oxidized metal Ionic complex , sometimes it can be prepared by the interaction of ligand and low oxidation metal ions in the presence of oxidant. For example, in the presence of air or oxygen, ammonia reacts with cobalt (II) brine solution to generate cobalt (III) Ammonia complex 。 Low oxidation metal ion complexes, sometimes in reducing agent In the presence of the ligand Metal salt Function. For example, by CoCO3 and H2 And CO to prepare Co2 (CO) 8, where H2 is a reducing agent and CO is ligand It is also a reducing agent.

Utilizing heat decomposition method , by heating some Complex Other complexes can be prepared, for example, cis - [Cr (en) 2Cl2] Cl can be prepared by heating [Cr (en) 3] Cl3.

Main reactions

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Acid-base reaction

Coordination chemistry (2 sheets)

because Hydrated metal ions dissociation , generate protons, and metal ions are usually acidic in aqueous solutions, such as: K

Is the acid dissociation constant, which can be used to measure the acidity of hydrated metal ions Electronic configuration of Generally speaking, metal ions have high charge and small radius, and the electronic configuration is conducive to Polarization When, the acidity is high; On the contrary, it is small. This dissociation reaction can continue, and with polymerization olation or Oxygenation Dual core and multi-core of Complex , such as: other materials containing protons that can be dissociated ligand , NH3 ethylenediamine and Organic acid Etc.

Substitution reaction

finger ligand replace Complex The reaction of another ligand. according to Substitution reaction It is often divided into active complexes and Inert complex 。 Water substituted in metal hydrate complexes reaction rate Often used as a measure of activity or inertia. Substituent It can be water molecule or other ligand. If it is the former, it can be marked with atom O (represented by symbol O) Tracer 。 For example: [Al (H two O) six 】+6H two O=【Al(H two O) six 】+6H two O

various Hydrated metal ions There is a great difference in the rate of substitution between the coordination water molecules of. for example alkali metal Hydrated ion The substitution reaction rate constant of is 10 eight ～10 nine The hydrated ions of aluminum and gallium are 1-10. The size of the ions and the amount of the electric charge have obvious effects on the reaction rate. The larger the radius, the faster the exchange of ions with the same charge and structure; With the same size of ions, the higher the charge, the slower the exchange. other ligand The reaction rate of the coordination water molecules in the substituted hydrated metal ions seldom depends on the properties of the ligands, but is often consistent with the exchange rate of the water molecules, that is, depends on the properties of the hydrated metal ions.

Electronics transfer reaction

It refers to the occurrence between two complexes electron transfer Reaction. For example, if [Fe (CN) 6] (Fe is the labeled atom) solution is mixed with [Fe (CN) 6], the former will lose an electron, and the latter will get an electron. The reaction is: [Fe (CN) 6]+[Fe (CN) 6] - →

【Fe(CN)6】+【Fe(CN)6】

Coordination chemistry

Exchange action Complete in 1 minute. This is the same metal and the same ligand Of Complex Electronics of transfer reaction 。 The electron transfer of different metals and different ligands is as follows:

application

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Coordination chemistry and inorganic, analytical, organic and physical chemistry Closely related to biochemistry Pharmaceutical chemistry 、 Agrochemistry And so on. It is widely used in chemistry and chemical industry.

The extraction and separation of metals Hydrometallurgy The process uses metal Complex Formation, such as nickel, copper and cobalt ammonia Solution extraction. stay nuclear reaction Beryllium produced in can be extracted with benzene solution of thiophenyl trifluoroacetone. Sodium cyanide It is commonly used to separate gold from ores. carbon monoxide It can be used for the purification of nickel.

chemical analysis

Coordination reaction occurs in the Gravimetric analysis 、 Capacity analysis and Photometric analysis It is widely used in Chromogenic agent 、 indicator 、 Precipitant , titrant Extractant 、 Masking agent Etc. For example, fluorine ion can be used as a masking agent to form colorless and stable [FeF6] with iron (III), which is in use Iodometry The interference of iron (Ⅲ) ion is avoided when measuring copper; with Diacetyl dioxime As a precipitant, nickel and palladium can be generated simultaneously Chelate Precipitation: nickel precipitation is soluble in acid, while palladium precipitation is insoluble, so nickel and palladium can be separated and identified; With thiocyanate as color developing agent, it can form blood red Complex To identify the existence of Fe. EDTA（ EDTA ）It can form complexes with most metal ions with different stability Titrimetric analysis An excellent titrant in the solution PH value and adding masking agent demaskingagent With EDTA, the contents of various metal ions can be titrated quantitatively from their mixed solutions, eliminating the step of separating interfering elements.

Catalysis

Transition metal compounds can olefin 、 Alkyne Formation of coordination with various unsaturated molecules such as carbon monoxide Complex And activate these molecules to form new compounds. For example, hydrogen of olefins formaldehyde In the chemical reaction, olefins, hydrogen and carbon monoxide form complexes with cobalt catalysts, and finally form aldehydes (R is alkyl): RCH=CH2+CO+H2 - → RCH2CH2CHO

Some Metal catalyst It can convert olefins into POLYMER 。 For example, set Titanium chloride (III) and Alkyl aluminium After coordination, it can be used as a catalyst to make olefins Directed polymerization become Polymer compound 。

Bibliography

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Dianbang Chief Editor: Coordination Chemistry（ inorganic chemistry Series), Science Press Beijing, 1987. 　J. C.Bailar, Jr. ,ed.,The Chemistry of the Coor-dination Compounds,Van Nostrand Reinhold,New York,1956. 　F. Basolo and R.C.Johnson,Coordination Chemis-try,The Study of Metal Complexes,Benjamin,New York,1964.

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