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

2. Complexes
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]

3. Coordination Chemistry
Metal Complex
Central meal Atom – Ligands [ M – L ]
Metals – Acceptors –
take lone pair of electrons from Ligands
Small size & High positive charge density
Vacant orbital of suitable energy
Example – transition metals
Ligands – Donors
They are usually anions, sometimes cations or polar molecules.
The must have lone pairs to interact with metal

4. What is Coordination?
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.

5. Metal-Ligand Bond
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) CN- (aq)  [Fe(CN)6]3-(aq)
Lewis base
Ni2+(aq) NH3(aq)  [Ni(NH3)6]2+(aq)
Lewis acid
Complex ion

6. Ligands Polydentate* Monodentate
Ligands are classified according to the number of donor atoms
Ligands
Monodentate
Bonded thru One donor atom
Polydentate*
Bonded thru More than one donor atom
Bidentate
Tridentate
Tetradentate
Pentadentate
Hexadentate
*If the complex has a closed ring structure it is called Chelate
And the ligand is called Chelating ligand.

7. Ligands
Monodentate
H2O, CN-, NH3, NO2-, SCN-, OH-, X- (halides), CO, O2-
Bidentate
oxalate ion = C2O42-
ethylenediamine (en) = NH2CH2CH2NH2
ortho-phenanthroline (o-phen)

8. Ligands * * * * * * *Donor Atoms oxalate ion ethylenediamine
ortho-phenanthroline * *
*Donor Atoms

9. Ligands
EDTA * * * * * *
*Donor Atoms

10. Chelating Agents
Porphyrins are complexes containing a form of the porphine molecule shown at right.
Important biomolecules like heme and chlorophyll are porphyrins.

11. Polydentate Ligands
Ethylenediaminetetraacetate, abbreviated EDTA, has six donor atoms.
Wraps around the central atom like an octopus

12. Coordination Chemistry - Terms
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
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.

13. Coordination Chemistry - Terms
Complex ion = sum of charges on the metal and the ligands
[Fe(CN)6]3- +3
6(-1)
Neutral complex molecule = sum of charges on metal, ligands, and counterbalancing ions is zero

14. Nomenclature of Coordination Compounds: IUPAC Rules
1. One word or Two words-
Molecular complex – One word name
[Pt(NH3)2Cl2] Diamminedichloroplatinum(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

15. Nomenclature [Ag(NH3)2][Ag(CN)2] Diamminesilver(I) dicyanoargentate(I)
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) [

16. Name if in Cationic Complex Name if in Anionic Complex
Nomenclature
2. Naming the Central metal atom –
2.1 Name -
For neutral and cationic complex – Name of metal is as it is.
For anionic complex - suffix -ate appended to the name of the metal
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

17. 2. Naming the Central metal atom
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)

18. The oxalate ion is a bidentate ligand.
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.

19. Nomenclature
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

20. Nomenclature – 3.1Name of the Ligand
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+

21. Nomenclature – f) Ligands are listed alphabetically
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) 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

22. Nomenclature 3.3 Bridging ligands have the prefix m
[(NH3)4Co(OH)(NH2)Co(NH3)4]4+
m-amido-m-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) -m- dihydroxotetrachloroiron(III)
4. Isomer designations come before the rest of the name and in italics
cis-diamminedichloroplatinum(II)
trans-diamminedichloroplatinum(II) OH OH

23. Examples [Fe(CO)5 ] Pentacarbonyliron(0)
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)

24. A chemical mystery Same metal, same ligands, different number of ions when dissolved

25. Werner’s Theory Metal ions have primary and secondary valences.
Primary valence equal the metal’s oxidation number
Secondary valence is the number of atoms directly bonded to the metal (coordination number)
Primary valences are ionizable and non – directional.
Secondary valences are non – ionizable and directional and give the geometry and shape of the molecule.
Sometimes ions satisfying the primary valence play a dual role and also satisfy the sec. valence.

26. Werner’s Theory
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.

27. Mol. Formula CoCl3 ∙ 6 NH3 CoCl3 ∙ 5 NH3 Complex [Co(NH3)6] Cl3
[Co(NH3)5Cl] Cl2
Ionisation
[Co(NH3)6] Cl-
[Co(NH3)5Cl] Cl
No. of ions
1 + 3 = 4
1 + 2 = 3
Structure
Pri. Valence
3 Cl- ions
Sec. Valence
6 NH3 molecules
5 NH3 molecules
1 Cl- ion ( dual role )
No. of Cl- precipitated on adding BaCl2 3 2

28. Mol. Formula CoCl3 ∙ 4 NH3 CoCl3 ∙ 3 NH3 Complex Co(NH3)4Cl2] Cl
Ionization
[Co(NH3)4 Cl 2] 1+ + Cl-
Non – ionising complex
No. of ions
1 + 1 = 2
Structure
Pri. Valence
3 Cl- ions
Sec. Valence
4 NH3 molecules
2 Cl- ion ( dual role )
3 NH3 molecules
3 Cl- ion ( dual role )
No. of Cl- precipitated on adding BaCl2 1

29. Werner’s Theory & Isomerism
Co(NH3)4Cl2] Cl – Coord. no. 6
Theoretically 3 shapes possible
Hexagonal Planar - 3 isomers
Trigonal Prism – 3 isomers Cl Cl Cl
NH3
NH3
NH3
NH3
NH3 Cl
NH3
NH3 Cl
NH3
NH3
NH3
NH3
NH3 Cl
NH3 Cl Cl
NH3
NH3
NH3 Cl Cl
NH3
NH3
NH3
NH3 Cl
NH3
NH3 Cl
NH3
NH3

30. 3. Octahedra - Cl Cl Cl Pt Pt Cl Two isomers possible.
NH3
NH3
NH3 Cl Pt Pt
NH3
NH3
NH3
NH3 Cl
NH3
Two isomers possible.
Werner could isolate TWO isomers hence concluded that the complex is Octahedra

31. Cis – trans – isomers in Octahedra shape

32. Sidwick's theory of effective atomic number
In 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 = +3
no. of electrons on Co3+ ion = = 24
Each ammonia ligand gives one pair of electron,
no. of electrons given by 6 ammonia molecules = 6 * 2 = 12
Total no. of electrons present on Co3+ now = = 36
EAN of Co3+ = 36
36 is atomic no. of Krypton.

33. Deffects in Sidwick's theory -
Examples of EAN rule
Though EAN rule is applicable to a number of cases, there are several complexes which do not follow this rule.
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
=36 Kr Co 27
[Co(NH3)6]3+ 3+ 3
=36 Kr Ni 28
[Ni(CO)4] 8
28-0+8=36 Kr Cu 29
[Cu(NH3)4]+ 1+ 1
29-1+8=36 Kr Zn 30
[Zn(H2O)4]2+
30-2+8=36 Kr Pd 46
[Pd(NH3)6]4+ 4+ 4
=54 Xe Pt 78
[Pt(Cl)6]2-
=86 Rn Cr 24
[Cr(NH3)6]3+
=35
K3[Fe(CN6)]
=35
[Ni(NH3)6]2+
=38
Deffects in Sidwick's theory -
Many well known complexes do not follow EAN rule.
The theory does not predict magnetic behaviour of the complexes.
The theory does not comment on the geometries of the complexes.