LECTURE 4LECTURE 4

THEME: Complex compound in biological systems.

associate prof. Dmukhalska Ye. B.associate prof. Dmukhalska Ye. B.

Outline

1. Concept of complex compounds and complexing process. Nomenclature of complex compounds. Types of complexes.

2. Structure of complex compounds. Isomerism of complex compounds. Chemical bonds in complex compounds molecule.

3. Stability of complexes and influence of different factors on it.

4. Biological role of complex compounds. Usage of complexing in chemistry.

•Coordination compounds are the compounds in which the central atom (usually metallic), (usually metallic), is linked to а number of ions or neutral molecules by coordinate bonds i.е. by donation of lone pairs of electrons by these ions or neutral molecules to the central metal atom.

• nickel tetracarbonyl, [Ni(CO)4]

A A coordination complexcoordination complex

Complex compounds

А) Structure

CuSO4 + 4 NH3 = [Cu (NH3)4] SO4

[Cu (NH3)4] SO4

Complex compound• Cu2+ - central atom •NH3 – ligand• [Cu (NH3)4]2+ - complex ion• SO4

2- -anion

Aqueous solutions that contain [Ni(H2O)6]2+, [Ni(NH3)6]2+ and [Ni(en)3]2+ (from left to right). The two solutions on the right were prepared by adding ammonia and ethylenediamine, respectively, to aqueous nickel(II)

nitrate.

Werner’s TheoryWerner’s Theory• Alfred Werner suggested in Alfred Werner suggested in

1893 that metal ions exhibit 1893 that metal ions exhibit what he called what he called primaryprimary and and secondarysecondary valences. valences.– Primary valences were the Primary valences were the

oxidation number for the oxidation number for the metal (+3 on the cobalt at the metal (+3 on the cobalt at the right).right).

– Secondary valences were the Secondary valences were the coordination number, the coordination number, the number of atoms directly number of atoms directly bonded to the metal (6 in the bonded to the metal (6 in the complex at the right).complex at the right).

Charge coordination number example

of the metal ion +1 2

Ag+, Cu+

+2 4, 6 Cu2+, Zn2+, Pd2+, Pt2+

+3 6, 4 Pt4+, Cr3+, Co3+, Fe3+

+4 8 Sn4+

Co-ordination Werner’s theory

•The species formed by linking of а number of ions or molecules by co-ordinate bonds to the central metal atom (or ion) carries positive or negative charge, it is called a complex ion (coordination sphera). [Fe(СN)6]

4-, [Cu(NH3)4]2+,

[Ag(CN)2]-

Coordination sphere.Coordination sphere.

• The central atom and the ligands The central atom and the ligands which are directly attached to it are which are directly attached to it are enclosed in square brackets and are enclosed in square brackets and are collectively termed as the collectively termed as the coordination sphere.coordination sphere.

Metal-Ligand BondMetal-Ligand Bond

• This bond is formed between a Lewis This bond is formed between a Lewis acid and a Lewis base.acid and a Lewis base.– The ligands (Lewis bases) have nonbonding The ligands (Lewis bases) have nonbonding

electrons.electrons.– The metal (Lewis acid) has empty orbitals.The metal (Lewis acid) has empty orbitals.

• Transition metals act as Lewis acidsTransition metals act as Lewis acids•Form complexes/complex ionsForm complexes/complex ions

FeFe3+3+(aq) + 6CN(aq) + 6CN--(aq) (aq) [Fe(CN) [Fe(CN)66]]3-3-(aq)(aq)

NiNi2+2+(aq) + 6NH(aq) + 6NH33(aq) (aq) [Ni(NH [Ni(NH33))66]]2+2+(aq)(aq)

Complex with a net charge = complex ionComplex with a net charge = complex ion

Complexes have distinct propertiesComplexes have distinct properties

Lewis acid Lewis base

Complex ion

Lewis acid Lewis base

Complex ion

• Coordination compoundCoordination compound– Compound that contains 1 or more Compound that contains 1 or more

complexescomplexes– ExampleExample

•[Co(NH[Co(NH33))66]Cl]Cl33

•[Cu(NH[Cu(NH33))44][PtCl][PtCl44]]

•[Pt(NH[Pt(NH33))22ClCl22]]

•The donor atoms, molecules or anions, which donate а pair of electrons to the metal atom and form co-ordinate bond with it are called ligands.

• LigandsLigands– classified according to the number of donor classified according to the number of donor

atomsatoms– ExamplesExamples

•monodentate = 1monodentate = 1

•bidentate = 2bidentate = 2

•tetradentate = 4tetradentate = 4

•hexadentate = 6hexadentate = 6

•polydentate = 2 or more donor atomspolydentate = 2 or more donor atoms

chelating agents

LigandsLigands

•MonodentateMonodentate– Examples: Examples:

•HH22O, CNO, CN--, NH, NH33, NO, NO22--, SCN, SCN--, OH, OH--, X, X--

(halides), CO, O(halides), CO, O2-2-

– Example ComplexesExample Complexes

•[Co(NH[Co(NH33))66]]3+3+

•[Fe(SCN)[Fe(SCN)66]]3-3-

LigandsLigands• BidentateBidentate

– ExamplesExamples

•oxalate ion = Coxalate ion = C22OO442-2-

•ethylenediamine (en) = ethylenediamine (en) = NHNH22CHCH22CHCH22NHNH22

•ortho-phenanthroline (o-phen)ortho-phenanthroline (o-phen)– Example ComplexesExample Complexes

•[Co(en)[Co(en)33]]3+3+

•[Cr(C[Cr(C22OO44))33]]3-3-

•[Fe(NH[Fe(NH33))44(o-phen)](o-phen)]3+3+

LigandsLigandsoxalate ion ethylenediamine

CC

O

O O

O 2-CH2

H2NCH2

NH2

NCH

CH

CH

CHCHCH

HC

HCN

CC

C

C

ortho-phenanthroline

Donor

Atoms:*

* ** *

**

LigandsLigandsoxalate ion ethylenediamine

O

C

MM N

CH

LigandsLigands

•ChelationChelation is a process in which a is a process in which a polydentate ligand bonds to a metal ion, polydentate ligand bonds to a metal ion, forming a ring. The complex produced by this forming a ring. The complex produced by this process is called a chelate, and the process is called a chelate, and the polydentate ligand is referred to as a polydentate ligand is referred to as a chelating agent.chelating agent.– ethylenediaminetetraacetate (EDTA) = ethylenediaminetetraacetate (EDTA) =

(O(O22CCHCCH22))22N(CHN(CH22))22N(CHN(CH22COCO22))224-4-

– Example ComplexesExample Complexes

•[Fe(EDTA)][Fe(EDTA)]-1-1

•[Co(EDTA)][Co(EDTA)]-1-1

CH2N

CH2

CH2

C

C

CH2 N

CH2

CH2 C

C

O

O

O

O

O O

OO

EDTA

LigandsLigands * Donor Atoms

*

* *

*

**

EDTALigandsLigands

C

O

N

H

M

EDTALigandsLigands

• Some important characteristics of chelates.Some important characteristics of chelates.• (i) Chelating ligands form more stable complexes (i) Chelating ligands form more stable complexes

than the monodentate analogs. This is called than the monodentate analogs. This is called chelating effectchelating effect..

• (ii) Chelating ligands, which do not contain double (ii) Chelating ligands, which do not contain double bonds e.g. ethylenediamine form five membered bonds e.g. ethylenediamine form five membered stable rings. The chelating ligands such as stable rings. The chelating ligands such as acetylacetone form six membered stable ring acetylacetone form six membered stable ring complexes.complexes.

• (iii) Ligands with large groups form unstable rings (iii) Ligands with large groups form unstable rings than the ligands with smaller groups due to steric than the ligands with smaller groups due to steric hindrance.hindrance.

• The complexes formed by Cu (II) and The complexes formed by Cu (II) and Pt (II) ions with ethylenediamine are Pt (II) ions with ethylenediamine are metal chelates represented as metal chelates represented as follows:follows:

Coordination numberCoordination number

• The number of ligand donor atoms that surround The number of ligand donor atoms that surround a central metal ion in a complex is called the a central metal ion in a complex is called the coordination number coordination number of the metalof the metal

• Originally, a complex implied a reversible Originally, a complex implied a reversible association of molecules, atoms, or ions through association of molecules, atoms, or ions through weak chemical bonds.weak chemical bonds.

• [Ag(СN)[Ag(СN)22]]--, [Cu(NН, [Cu(NН33))44]]

2+2+ and [Cr(Н and [Cr(Н22О)О)66]]3+3+

Common Geometries of Complexes

Linear

Coordination Number Geometry

2

Example: [Ag(NH3)2]+

Common Geometries of ComplexesCoordination Number

Geometry4tetrahedral

square planarExample:

[Ni(CN)4]2-

Examples: [Zn(NH3)4]2+, [FeCl4]-

Common Geometries of ComplexesCoordination Number

Geometry6

octahedral

Examples: [Co(CN)6]3-, [Fe(en)3]3+

Charge on the complex ion.Charge on the complex ion.

• The charge carried by а complex ion The charge carried by а complex ion is the algebraic sum of the charges is the algebraic sum of the charges carried by central metal ion and the carried by central metal ion and the ligands coordinated to the central ligands coordinated to the central metal ion. metal ion.

• [Ag (CN)[Ag (CN)22]-]-

• [Cu (NH[Cu (NH33))44]]2+2+

[Fe(CN)6]3-

Complex charge = sum of charges on the metal and the ligands

[Fe(CN)6]3-

Complex charge = sum of charges on the metal and the ligands

+3

6(-1)

[Co(NH3)6]Cl2

Neutral charge of coordination compound = sum of charges on metal,

ligands, and counterbalancing ions

neutral compound

+2

6(0) 2(-1)

Oxidation number or oxidation Oxidation number or oxidation statestate..• It is а number that represents an electric charge

which an atom or ion actually has or appears to have when combined with other atoms,

• oxidation number of copper in [Cu(NH3)4]2+ is +2 but

coordination number is 4.• oxidation number of Fe in [Fe(СN)6]

3- is + 3 but the coordination number is 6.

• (i) [Cu (NНЗ)4]SO4.

• (ii) Fe in [Fe (СN)6]3-

• (iii)К3[Fe(С2О4)3].

• (iv) [Ni(CO)4].

[Co(NH3)6]Cl2

Neutral charge of coordination compound = sum of charges on metal,

ligands, and counterbalancing ions

neutral compound

+2

6(0) 2(-1)

Nomenclature of Nomenclature of Coordination Compounds: Coordination Compounds:

IUPAC RulesIUPAC Rules• The cation is named before the anionThe cation is named before the anion

• When naming a complex:When naming a complex:– Ligands are named firstLigands are named first

•alphabetical orderalphabetical order– Metal atom/ion is named lastMetal atom/ion is named last

•oxidation state given in Roman oxidation state given in Roman numerals follows in parenthesesnumerals follows in parentheses

– Use no spaces in complex name Use no spaces in complex name

Naming Coordination CompoundsNaming Coordination Compounds

Names of Some Common Metallate Names of Some Common Metallate AnionsAnions

Names of Some Common LigandsNames of Some Common Ligands

Examples of Complexes withExamples of Complexes withVarious Coordination NumbersVarious Coordination Numbers

• [Co(NН[Co(NН33))66]Cl]Cl33, hexaamminecobalt (III) , hexaamminecobalt (III)

chloride.chloride.

• KK22[PtCl[PtCl66], potassium hexachloroplatinate ], potassium hexachloroplatinate

(IV).(IV).

• [Co(NO[Co(NO22)(NH)(NH33))33], triamminetrinitrocobalt ], triamminetrinitrocobalt

(III)(III)

• [PtCl[PtCl44(NH(NH33))22], ],

diamminetetrachloroplatinum (IV).diamminetetrachloroplatinum (IV).

Types of complexes.Types of complexes. • (i) А complex in which the complex ion (i) А complex in which the complex ion

carries а net positive charge is called carries а net positive charge is called cationic complex: [Co(NНcationic complex: [Co(NН33)])]

3+3+, [Ni(NH, [Ni(NH33))66]]2+2+

• (ii) А complex in which the complex ion (ii) А complex in which the complex ion carries а net negative charge is called carries а net negative charge is called anionic complex: [Ag(CN)anionic complex: [Ag(CN)22]]

--, [Fe (CN), [Fe (CN)66]]4-4-

• (iii) А complex carrying no net charge is (iii) А complex carrying no net charge is called а neutral complex or simply а called а neutral complex or simply а complex:complex:

• [Ni(CO)[Ni(CO)44], [CoCl], [CoCl33 (NН (NН33))33]]

1. With one central atom• Ammonia complex [Cu(NH3)4]SO4

• Aqua complex[Al(H2O)6]Cl3• acidic complex K2[PtCl4]• complex with difference ligands K[Pt(NH3)Cl3]• cyclic (chelates)

Polycentral compoyndsChain [Cr(NH3)5 – OH – (NH3)Cr]Cl3 chelaes (CO)5Mn – Mn(Co)5

Main types of complex compounds

MeO

O

O

O

C

CMe

NH2

NH2

CH2

CH2

CO

CH2 CH2

N NH2CHOOC COOHCH2

MeH2C CH2

CO

O O

IsomerismIsomerism

• IsomersIsomers– compounds that have the same compounds that have the same

composition but a different composition but a different arrangement of atomsarrangement of atoms

•Major TypesMajor Types– structural isomersstructural isomers– stereoisomersstereoisomers

Structural IsomersStructural Isomers• Structural IsomersStructural Isomers

– isomers that have different bondsisomers that have different bonds

• Coordination-sphere isomersCoordination-sphere isomers– differ in a ligand bonded to the metal in the differ in a ligand bonded to the metal in the

complex, as opposed to being outside the complex, as opposed to being outside the coordination-spherecoordination-sphere

• ExampleExample

[Co(NH[Co(NH33))55Cl]Br vs. [Co(NHCl]Br vs. [Co(NH33))55Br]ClBr]Cl

Coordination-Sphere Coordination-Sphere IsomersIsomers

•ExampleExample

[Co(NH[Co(NH33))55Cl]Br vs. [Co(NHCl]Br vs. [Co(NH33))55Br]ClBr]Cl

•Consider ionization in waterConsider ionization in water

[Co(NH[Co(NH33))55Cl]Br Cl]Br [Co(NH [Co(NH33))55Cl]Cl]++ + Br + Br--

[Co(NH[Co(NH33))55Br]Cl Br]Cl [Co(NH [Co(NH33))55Br]Br]++ + Cl + Cl--

Coordination-Sphere Coordination-Sphere IsomersIsomers• ExampleExample

[Co(NH[Co(NH33))55Cl]Br vs. [Co(NHCl]Br vs. [Co(NH33))55Br]ClBr]Cl

• Consider precipitationConsider precipitation

[Co(NH[Co(NH33))55Cl]Br(aq) + AgNOCl]Br(aq) + AgNO33(aq) (aq) [Co(NH[Co(NH33))55Cl]NOCl]NO33(aq) + AgBr(s) (aq) + AgBr(s)

[Co(NH[Co(NH33))55Br]Cl(aq) + AgNOBr]Cl(aq) + AgNO33(aq) (aq) [Co(NH[Co(NH33))55Br]NOBr]NO33(aq) + AgCl(aq) (aq) + AgCl(aq)

Structural IsomersStructural Isomers•Linkage isomersLinkage isomers

– differ in the atom of a ligand differ in the atom of a ligand bonded to the metal in the bonded to the metal in the complexcomplex

•ExampleExample

– [Co(NH[Co(NH33))55(ONO)](ONO)]2+2+ vs. vs. [Co(NH[Co(NH33))55(NO(NO22)])]2+2+

Linkage IsomersLinkage Isomers

StereoisomersStereoisomers– Isomers that have the same bonds, Isomers that have the same bonds,

but different spatial arrangementsbut different spatial arrangements

•Geometric isomersGeometric isomers– Differ in the spatial arrangements Differ in the spatial arrangements

of the ligands of the ligands – Have different chemical/physical Have different chemical/physical

propertiesproperties

•different colors, melting points, different colors, melting points, polarities, solubilities, reactivities, polarities, solubilities, reactivities, etc. etc.

cis isomer

trans isomerPt(NH3)2Cl2

Geometric IsomersGeometric Isomers

cis isomer

trans isomer[Co(H2O)4Cl2]+

Geometric IsomersGeometric Isomers

StereoisomersStereoisomers

•Optical isomersOptical isomers– isomers that are isomers that are

nonsuperimposable mirror imagesnonsuperimposable mirror images

•said to be “chiral” (handed)said to be “chiral” (handed)

•referred to as enantiomersreferred to as enantiomers– A substance is “chiral” if it does A substance is “chiral” if it does

not have a “plane of symmetry”not have a “plane of symmetry”

mirro

r pla

ne

cis-[Co(en)2Cl2]+

Example 1

Thank you for attention