Coordination Chemistry Paper III Unit 1 No. of Classes - 12 1 .

Coordination Chemistry

Paper III Unit 1

No. of Classes - 12

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A central metal atom bonded to a group of

molecules or ions is a metal complex.

Metal complexes are coordination compounds.

◦ Example Complexes

[Co (NH3)6 ]Cl3

K 4 [Fe(SCN)6 ]

[Cu(NH3)4][PtCl4]

[Pt(NH3)2Cl2]


Metal Complex

Central meal Atom – Ligands [ M – L ]

Metals – Acceptors –

1. take lone pair of electrons from Ligands

2. Small size & High positive charge density

3. Vacant orbital of suitable energy

4. Example – transition metals

Ligands – Donors

1. They are usually anions, sometimes cations or polar molecules.

2. The must have lone pairs to interact with metal


When an orbital from a ligand with lone pair overlaps with an

empty orbital from a metal a coordinate covalent bond is formed

M L

So ligands must have lone pairs of electrons.


This bond is formed between a Lewis acid and a Lewis base.

◦ The ligands (Lewis bases) have nonbonding electrons.

◦ The metal (Lewis acid) has empty orbitals.


Fe3+(aq) + 6CN- (aq) [Fe(CN)6]3-(aq)Lewis base

Ni2+(aq) + 6NH3(aq) [Ni(NH3)6]2+(aq)

Lewis acid Complex ion

Ligands are classified according to the number of donor atoms

*If the complex has a closed ring structure it is called Chelate

And the ligand is called Chelating ligand.


Monodentate

H2O, CN-, NH3, NO2-, SCN-, OH-, X- (halides), CO, O2-

Bidentate

oxalate ion = C2O42-

ethylenediamine (en) = NH2CH2CH2NH2

ortho-phenanthroline (o-phen)


oxalate ion ethylenediamine

CC

O

O O

O 2-CH2

H2NCH2

NH2

NCH

CH

CH

CHCHCH

HC

HCN

CC

C

C

ortho-phenanthroline

*Donor Atoms

* ** *

**


CH2N

CH2

CH2

C

C

CH2 N

CH2

CH2 C

C

O

O

O

O

O O

OO

EDTA

*Donor Atoms

*

* *

*

**


Porphyrins are complexes

containing a form of the

porphine molecule shown at

right.

Important biomolecules like

heme and chlorophyll are

porphyrins.


Ethylenediaminetetraacetate,

abbreviated EDTA, has six donor atoms.

Wraps around the central atom like an octopus


The atom that supplies the

lone pairs of electrons for the

metal-ligand bond is the

donor atom.

The number of these atoms is

the coordination number.


Coordination sphere - Metal and ligands bound to it. [ M L (n) ]

Coordination number - Number of donor atoms bonded to the central metal atom

or ion in the complex

[Fe(CN)6]3-

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

+3 6(-1)


Neutral complex molecule = sum of charges on metal, ligands, and counterbalancing ions is zero

1. One word or Two words-

i. Molecular complex – One word name [Pt(NH3)2Cl2] Diamminedichloroplatinum(II)

ii. Ionic complex – Two words -Name of cation & Name of anion

The cation is named before the anion

a) Cationic complex – [ ML ] Y [ML]+ + Y -

cpx. cation

[Co (NH3)6 ]Cl3 Hexaamminecobolt(III) Chloride

[Cr(NH3)3(H2O)3]Cl3 Triamminetriaquachromium(III) chloride


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[

b) Anionic complex – X [ ML ] X + + [ ML ]-

Cpx. Anion

K 4 [Fe(CN)6 ] Potassium hexacyanoferrate(II)

c)When there are two coordination spheres the cation is named first followed by anion and each coordination sphere is named separately.

[Ag(NH3)2][Ag(CN)2] Diamminesilver(I) dicyanoargentate(I)

NomenclatureNomenclature


2. Naming the Central metal atom –

2.1 Name -

a)For neutral and cationic complex – Name of metal is as it is.

b)For anionic complex - suffix -ate appended to the name of the metal

NomenclatureNomenclature

Transition Metal Name if in Cationic Complex Name if in Anionic Complex

Sc Scandium Scandate

Ti titanium titanate

V vanadium vanadate

Cr chromium chromate

Mn manganese manganate

Fe iron ferrate

Co cobalt cobaltate

Ni nickel nickelate

Cu Copper cuprate

Zn Zinc zincate


2.2 Oxidation state - Name followed by its oxidation state in Roman

numerals in parenthesis. Knowing the charge on a complex ion and

the charge on each ligand, one can determine the oxidation number

for the metal.

Ex. [Pt(NH3)2Cl2] - x + (0*2) + (-1*2) = 0

x +0-2 = 0, x = +2

Diamminedichloroplatinum(II)

Na2 [NiCl4] Sodium tetrachloronickelate(II)

2. Naming the Central metal atom


Nomenclature

3. Naming the Coordination sphere -

In the coordination sphere the ligands are named first and Metal is

named last and its oxidation state given in Roman numerals follows in

parentheses. Use no spaces in name of complex ion.

[Pt(NH3)5Cl]Br3 Pentaamminechloroplatinum(IV) bromide

(NH4)2[Ni(C2O4)2(H2O)2] Ammonium diaquadioxalatonickelate(II)

The oxalate ion is a bidentate ligand.

3.1 Name of the Ligand –

a) The names of anionic ligands end with the suffix -o


Ligand Name

bromide, Br- bromo

chloride, Cl- chloro

cyanide, CN- cyano

hydroxide, OH- hydroxo

oxide, O2- oxo

fluoride, F- Fluoro

carbonate, CO32- carbonato

oxalate, C2O42- oxalato

sulfate, SO42- sulfato

thiocyanate, SCN- thiocyanato

thiosulfate, S2O32- thiosulfato

Sulfite, SO32- sulfito

Nomenclature


b) Neutral ligands are referred to by the usual name for the molecule

Example – ethylenediamine, Pyridine, Ethanol, Methyl amine.

Exceptions

Water, H2O : Aqua

Ammonia, NH3 :Ammine

Carbon monoxide, CO :Carbonyl

Nitric oxide, NO : Nitrosyl

c) Positive ligands – Their name ends with a suffix of - ium

Pyridinium. Nitronium NO+

Nomenclature – 3.1Name of the Ligand

3.2 - No. of ligands

a) Greek prefixes are used to indicate the number of each type of ligand when

more than one of same type is present in the complex

di-, 2; tri-, 3; tetra-, 4; penta-, 5; hexa-, 6

[Fe(NH3)6](NO3)3 Hexaammineiron(III) nitrate

Prefixes denoting the number of ligands are ignored when alphabetizing.

b) If the ligand name already contains a Greek prefix, use alternate prefixes

like bis-, 2; tris-, 3; tetrakis-,4; pentakis-, 5; hexakis-, 6

The name of the ligand is placed in parentheses

f) Ligands are listed alphabetically

[CoClBr(NH3)4]SO4 Tetraamminebromochlorocobalt(III) sulfate


Nomenclature –


3.3 Bridging ligands have the prefix

[(NH3)4Co(OH)(NH2)Co(NH3)4]4+

-amido--hydroxobis(tetraaminecobalt(III))When a complex has two or more metal atoms it is called Polynuclear and the metals are bonded through the bridging ligands.

(NH3)4Fe Fe(Cl)4

Tetraammineiron(III) -- dihydroxotetrachloroiron(III)

4. Isomer designations come before the rest of the name and in italics

cis-diamminedichloroplatinum(II)

trans-diamminedichloroplatinum(II)

Nomenclature Nomenclature

OH

OH


Examples

K3[Fe(CN)6] = potassium hexacyanoferrate(III)

K4[Fe(CN)6] = potassium hexacyanoferrate(II)

Na3[AlF6] = sodium hexafluoroaluminate(III)

[Co(NH3)3F3] = triamminetrifluorocobalt(III)

[Fe(NH3) 6] NO3 Hexaammineiron(III) nitrate

(NH4)2[CuCl4] Ammonium tetrachlorocuprate(II)

Na3[FeCl(CN)5] Sodium chloropentacyanoferrate(III)

K3[CoF6] Potassium hexafluorocobaltate(III)

[Co(SO4)(NH3)5]+. Pentaamminesulfatocobalt(III) ion

[Fe(OH)(H2O)5]2+ Pentaaquahydroxoiron(III) ion

[Fe(NH3)6][Cr(CN)6] Hexaammineiron(III) hexacyanochromate (III)

[Fe(CO)5 ] Pentacarbonyliron(0)

1. Metal ions have primary and secondary valences.

2. Primary valence equal the metal’s oxidation number

3. Secondary valence is the number of atoms directly bonded to the metal

(coordination number)

4. Primary valences are ionizable and non – directional.

5. Secondary valences are non – ionizable and directional and give the

geometry and shape of the molecule.

6. Sometimes ions satisfying the primary valence play a dual role and also

satisfy the sec. valence.

The central metal and the ligands directly bonded to it make

up the coordination sphere of the complex.

In CoCl3 ∙ 6 NH3, all six of the ligands are NH3 and the 3

chloride ions are outside the coordination sphere.


Mol. Formula

CoCl3 ∙ 6 NH3 CoCl3 ∙ 5 NH3

Complex [Co(NH3)6] Cl3 [Co(NH3)5Cl] Cl2

Ionisation [Co(NH3)6] 3+ + 3Cl- [Co(NH3)5Cl]2+ + 2Cl

No. of ions 1 + 3 = 4 1 + 2 = 3

Structure

Pri. Valence 3 Cl- ions 3 Cl- ions

Sec. Valence 6 NH3 molecules 5 NH3 molecules1 Cl- ion ( dual role )

No. of Cl- precipitated on adding BaCl2

3 2


Mol. Formula CoCl3 ∙ 4 NH3 CoCl3 ∙ 3 NH3

Complex Co(NH3)4Cl2] Cl [Co(NH3)3Cl3]

Ionization [Co(NH3)4 Cl 2] 1+ + Cl- Non – ionising complex

No. of ions 1 + 1 = 2 0

Structure

Pri. Valence 3 Cl- ions 3 Cl- ions

Sec. Valence 4 NH3 molecules 2 Cl- ion ( dual role )

3 NH3 molecules3 Cl- ion ( dual role )

No. of Cl- precipitated on adding BaCl2

1 0

Co(NH3)4Cl2] Cl – Coord. no. 6

Theoretically 3 shapes possible

1. Hexagonal Planar - 3 isomers

2. Trigonal Prism – 3 isomers

NH3

NH3

NH3

NH3

Cl

Cl

NH3

NH3

NH3

NH3

NH3

NH3

NH3NH3

Cl

Cl

Cl

Cl

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

NH3

Cl

ClCl

ClCl

Cl


3. Octahedra -

NH3

NH3

NH3

NH3

NH3

NH3NH3

NH3

Cl

Cl

Cl

Cl

Two isomers possible.

Werner could isolate TWO isomers hence concluded that the complex is Octahedra

Pt Pt


Cis – trans – isomers in Octahedra shapeCis – trans – isomers in Octahedra shape

Trans -

Cis -


Sidwick's theory of effective atomic numberIn complexes, metal atom accept lone pair of electrons donated by the ligand

for bond formation. It proposes that a metal ion will continue to accept

lone pair of electrons till its effective atomic number becomes equal to

the atomic no. of the next higher noble gas.

( Effective atomic number - it is the total no. of electrons present on a metal

atom i.e. no. of electrons present on the metal atom – e lost during

formation of ion + those gained from the ligands. Each monodentate ligand gives one lone pair of electron.) Calculation of EAN - [Co(NH3)6]Cl3 -

atomic no. of cobalt = 27, oxidation state of Co = +3no. of electrons on Co3+ ion = 27 - 3 = 24Each ammonia ligand gives one pair of electron,no. of electrons given by 6 ammonia molecules = 6 * 2 = 12Total no. of electrons present on Co3+ now = 24 + 12 = 36EAN of Co3+ = 36

36 is atomic no. of Krypton.


Metal atom

at.no

complex O.S. of the metal ion

e- lost in ion formation

e- given by ligands

EAN / noble gas

Fe 26 K4[Fe(CN6)] 2+ 2 12 26-2+12=36 KrCo 27 [Co(NH3)6]3+ 3+ 3 12 27-3+12=36 KrNi 28 [Ni(CO)4] 0 0 8 28-0+8=36 KrCu 29 [Cu(NH3)4]+ 1+ 1 8 29-1+8=36 KrZn 30 [Zn(H2O)4]2+ 2+ 2 8 30-2+8=36 KrPd 46 [Pd(NH3)6]4+ 4+ 4 12 46-4+12=54 Xe

Pt 78 [Pt(Cl)6]2- 4+ 4 12 78-4+12=86 Rn

Cr 24 [Cr(NH3)6]3+ 3+ 3 12 24-3+12=35Fe 26 K3[Fe(CN6)] 3+ 3 12 26-3+12=35Ni 28 [Ni(NH3)6]2+ 2+ 2 12 28-2+12=38

Examples of EAN ruleThough EAN rule is applicable to a number of cases, there are several complexes which do not follow this rule.

Deffects in Sidwick's theory -

1.Many well known complexes do not follow EAN rule.

2.The theory does not predict magnetic behaviour of the complexes.

3.The theory does not comment on the geometries of the complexes.

Coordination Chemistry Paper III Unit 1 No. of Classes - 12 1 .

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Transcript of Coordination Chemistry Paper III Unit 1 No. of Classes - 12 1 .