Werner’s Theory Bonding in Complex

Some Important Terms Bonding in Metal Carbonyls

Nomenclature of Complex Stability of Complex

Isomerism in Complex Importance and Application

 Double salt Complex salt
● Formed by the combination of two or more ● Formed by the combination of two or
stable compounds in stoichiometric ratio. more stable compounds in
● Exist only in solid state. stoichiometric ratio.
● lose their identity in their aqueous ● Exist in both solid and liquid state.
solution. ● Does note lose their identity in their
● Dissociate completely into simple ions on aqueous solution.
dissolving in water. ● Does not dissociate completely into
● Ex: Carnallite [KCl.MgCl2.6H2O] simple ions on dissolving in water.
Mohr’s salt [FeSO4.(NH4)2SO4.6H2O] ● Potassiumhexacynoferrate
Potas alum [KAl(SO4).12H2O] K4[Fe(CN)6]

Fe(NH4)2(SO4)2.6H2O → Fe2+ + NH4+ + 2SO42- + 6 H2O

K4[Fe(CN)6] → 4K+ + [Fe(CN)6]4-
Werner’s theory
Alfred Werner was the first to formulate his ideas about the structures of coordination
compounds. It was the first successful explanation, became famous as the coordination
theory of complex compounds which is also known as Werner's Theory.

The postulates of Werner's Theory are given as -

● In coordination compounds metals show two types of valences - primary and
secondary.

● The primary valences are normally ionisable and are satisfied by negative ions. It is
equal to the oxidation state of the metal.

● The secondary valences are non ionisable. These are satisfied by neutral molecules or
negative ions. The secondary valence is equal to the coordination number and is fixed
for a metal.

● The ions/groups bound by the secondary linkages to the metal have characteristic
spatial arrangements corresponding to different coordination numbers.
Primery Valance

P.V. = Oxidation state of Central Metal Atom

= Total positive charge on Central Metal Atom

Secondary Valance
Denticity is the
S.V. = Coordination Number number of lone
= No. of Ligands × Denticity pair of electron
donated by a
ligand to CMA.
 Prectice session
Q.1. On the basis of the following observations made with aqueous solutions.
assign secondary valences to metals in the following compounds:

Moles of AgCl ppt

S. No. Formula
with excess AgNO3
1 PdCl2.4NH3 2
2 NiCl2.6H2O 2
3 PtCl4.2NHCl 0
4 CoCl3.4NH3 1
5 PtCl2.2NH3 0
Q.2 Calculate the PV and SV in the following complex salt.
(i) [Co(NH3)6]Cl3
(ii) [Pt(NH3)2Cl(NH2CH3)]Cl
(iii) [Ti(H2O)6]3+
(iv) [Co(NH3)4Cl(NO2)]Cl
(v) [NiCl4]2-
(vi) [Mn(H2O)6]2+
(vii) [Ni(NH4)4Cl(NO2)]Cl
(viii) [Co(en)3]3+
(ix) [Ni(CO)4]
Q.3. Explain the bonding in coordination compounds in terms of Werner’s
postulates.

Q.4. FeSO4 solution mixed with (NH4)2SO4 solution in 1:1 molar ratio gives the
test of Fe2+ ion but CuSO4 solution mixed with aqueous ammonia in 1:4 molar ratio
does not give the test of Cu2+ ion. Explain why?
 Some important Terms

❏ Coordination entity
❏ Central atom/ion
❏ Ligands
❏ Coordination number
❏ Coordination sphere
❏ Coordination polyhedron
❏ Oxidation number of central atom
❏ Homoleptic and heteroleptic complexes
 Coordination
Central Metal Atom Entity

K4[Fe(CN)6]
Counter ion Ligand
Or
Ionisation sphere Coordination
sphere
 Prectice session
Q.1. Explain with two examples each of the following: coordination entity, ligand,
coordination number, coordination polyhedron, homoleptic and heteroleptic.

Q.2. What is meant by unidentate, didentate and ambidentate ligands? Give two
examples for each.
Ligands and it's classification
● The ions or molecules bound to the central atom/ion in the coordination entity
are called ligands.
● It may be simple ions, small molecules, large molecules or even
macromolecules
● It acts as a lewis base.

Classification of Ligands
● Monodemtate / Unidentate
On the basis
● Bidentate / Didentate of DENTICITY
● Polydentate ● Ambidentate On the basis of
● Cheating DONATION

● Positive
On the basis
● Negative of CHARGE
● Neutral
IUPAC naming of coordination compounds
Format of the Name

For Neutral Coordination Sphere:

No of the ligand + Name of the ligand + Name of CMA (O.S.)

For Positive Coordination Sphere:

No of the ligand + Name of the ligand + Name of CMA (O.S.) Name of the Anion

For Negative Coordination Sphere:

Name of the Cation No of the ligand + Name of the ligand + CMA + ate (O.S.)
Naming of Ligands
Formula Name
Negative Ligands
H2O Aqua
Formula Name Formula Name
NH3 Ammine
X– Halido C2O42-(ox) Oxalato
CO Carbonyl
SO42- Sulphato S2O32- Thiosulphato Nutral
H2N(CH)2NH2 (en) Ethylenediamine Ligands
SO32- Sulphito CNO– Cyanato
CH3NH2 Methylamine
CO32- Carbonato CON– Isocyanato
C5H5N Pyridine
– 2-
CN Cyanido O Oxido
PPh3 Triphenylphosphine
– –
NC Isocyanido CH3COO Acetato

SCN– Thiocyanido HCOO– Formato Formula Name

NCS– Isothiocyanido OH– Hydroxido NO2+ Nitronium

NO2– NO3– Positive

Nitrito-N Nitrato NO+ Nitrosonium
Ligands
ONO– Nitrito-O N2H5+ Hydrazinium

EDTA4- Ethylenediaminetetraacetato (C6H5NH3)+ Anilinium

Naming of Central Metal Atom (CMA)
Name Name
Symbol Symbol
In +ve or neutral C.S. In -ve C.S. In +ve or neutral C.S. In -ve C.S.

Al Aluminium Aluminate Ag Silver Silverate

Cu Copper Cuprate Cr Chromium Chromate

Fe Iron Ferrate Mn Manganese Magnate

Co Cobalt Cobaltate Ni Nickel Nickelate

Zn Zinc Zincate Hg Mercury Mercurate

Au Gold Aurrate Pt Platinum Platinate

Most common oxidation states of some CMAs:

(Cu, Ag, Au) → +1, (Ag, Sn, Cu, Pb, Co, Fe, Ni, Pd, Pt) → +2
(Au, Co, Fe, Cr) → +3, (Sn, Pb, Ni, Pd, Pt) → +4
 Prectice session
Write down the IUPAC name of the following Complexes:
1) [Ni(CO)₄]
2) [Pt(NH₃)₄]
3) [Pt(NH3)2Cl(NO2)]
4) [Cr(NH₃)6]Cl3
5) [Cr(CO)6]
6) [Ni(en)₂]
7) [Co(en)₃]
8) [Co(NH3)3Cl3]
9) [Co(NH3)2(H2O)Cl3]
10) [PtCl4]
Write down the IUPAC name of the following Complexes:
1) [Co(NH3)6]Cl3
2) [Co(NH3)4Cl2]Cl
3) [Ti(H2O)6]3+
4) [Co(NH3)4Cl(NO2)]Cl
5) [Mn(H2O)6]2+
6) [Ni(NH3)6]Cl2
7) [Co(en)3]3+
8) [Co(NH3)5Cl]Cl2
9) [Pt(NH3)2Cl(NH2CH3)]Cl
10) [Co(NH3)5(CO3)]Cl
11) [CoCl2(en)2]Cl
Write down the IUPAC name of the following Complexes:
1) K3[Cr(C2O4)3]
2) Hg[Co(SCN)4]
3) K3[Fe(CN)6]
4) K3[Fe(C2O4)3]
5) K2[PdCl4]
6) [NiCl4]2-
7) K4[Fe(CN)6]
8) Na2[Zn(OH)4]
9) K3[CoCl6]
10) Na3[Cr(C2O4)3]
Using IUPAC norms write the formulas for the following:

1) Tetrahydroxidozincate(II)
2) Potassium tetrachloridopalladate(II)
3) Diamminedichloridoplatinum(II)
4) Potassium tetracyanidonickelate(II)
5) Pentaamminenitrito-O-cobalt(III)
6) Hexaamminecobalt(III) sulphate
7) Potassium tri(oxalato)chromate(III)
8) Hexaammineplatinum(IV)
9) Tetrabromidocuprate(II)
10) Pentaamminenitrito-N-cobalt(III)
11) Tetraammineaquachloridocobalt(III) chloride
12) Potassium tetrahydroxidozincate(II)
13) Potassium trioxalatoaluminate(III)
14) Dichloridobis(ethane-1,2-diamine)cobalt(III)
15) Tetracarbonylnickel(0)
16) Tetraamminediaquacobalt(III) chloride
17) Potassium tetracyanidonickelate(II)
18) Tris(ethane–1,2–diamine) chromium(III) chloride
19) Amminebromidochloridonitrito-N-platinate(II)
20) Dichloridobis(ethane–1,2–diamine)platinum(IV) nitrate
21) Iron(III) hexacyanidoferrate(II)
Isomerism In Coordination Compounds

Structural

Isomerism
Stereo
STRUCTURAL ISOMERS Coordination Isomerism:
● Different Coordination Spheres
Ionisation Isomerism: ● Same Overall Formula
● Same Molecular Formula ● Requires Multiple Metal Ions
● Different Ions in Solution ● Ligand Exchange
● Interchange of Ligand and Counter-ion ● Ex- [Co(NH₃)₆]³⁺[Cr(CN)₆]³⁻
● Ex- [Co(NH₃)₅SO₄]Br

Hydrate/Solvate Isomerism:
Linkage Isomerism:
● Form of Ionization Isomerism
● Ambidentate Ligands
● Different Water Locations
● Different Donor Atoms
● Ex- [Cr(H₂O)₆]Cl₃ (Violet), [Cr(H₂O)
● different connectivity of the ligand to
₅Cl]Cl₂·H₂O (Blue-green), [Cr(H₂O)
the central metal atom.
₄Cl₂]Cl·2H₂O (Green).
● Ex- [Co(NH₃)₅(NO₂)]²⁺
 STEREO ISOMERS
B) Coordination no. 6 :
GEOMETRICAL ISOMERISM Monodentate Ligand Bidentate Ligand

A) Coordination no. 4 Complex No. of Complex No. of

type Isomers type Isomers
(Square planer):
Ma6 × M(aa)3 ×
Monodentate Ligand Bidentate Ligand
Ma5b × M(aa)b2c2 3
Complex No. of Complex No. of
type Isomers type Isomers Ma4b2 2 M(aa)2b2 2

Ma4 × M(aa)2 × Ma4bc 2 M(ab)3 2

Ma3b × M(aa)(bb) × Ma3b3 2

Ma2b2 2 M(aa)b2 × Ma3b2c 3

Ma2bc 2 M(aa)bc 2 Ma2b2c2 5

Mabcd 3 Mabcdef 15
OPTICAL ISOMERISM
❏ If the sample of a compound can rotate the plane polerised light, it is said to
be optically active.
❏ They are also known as enantiomers (non superimposible mirror images).
❏ They always exist in pairs.

Principal of polerimeter
A) Coordination no. 4 :
❏ No isomers exist except Mabcd
(tetrahedral).
❏ Sqire planer complexes and
tetrahedral complexes except
Mabcd do not show optical
isomerism because of existence of
plane of symmetry.
B) Coordination no. 6 : Total no of stereo isomers
= no of geometrical isomers
❏ The Complex having 3 or more
+ no of optical isomers
than 3 different monodentate
ligands except Ma4bc is always
optically active.

❏ The Complex having 2 or more

than 2 bidentate ligands except
trans- M(aa)2l2 is always optically
active.

❏ If a molecule have any element

of symmetry (COS, POS, LOS), it
is said to be optically inactive.
 Prectice session
Q.1. Why is geometrical isomerism not Q.2. Draw structures of geometrical
possible in tetrahedral complexes isomers of [Fe(NH3)2(CN)4]--
having two different types of unidentate
ligands coordinated with the central
metal ion ?
Q.3. Out of the following two Q.4. Indicate the types of isomerism
coordination entities which is chiral exhibited by the following complexes and
(optically active)? draw the structures for these isomers:
(a) cis - [CrCl2(ox)2]3- (i) K[Cr(H2O)2(C2O4)2]
b) trans - [CrCl2(ox)2]3- (ii) [Co(en)3]Cl3
(iii) [Co(NH3)5(NO2)](NO3)2
(iv) [Pt(NH3)(H2O)Cl2]
Q.5. Give evidence that Q.7. How many geometrical isomers are
[Co(NH3)5Cl]SO4 and [Co(NH3)5(SO4)]Cl possible in the following coordination
are ionisation isomers. entities?
(i) [Cr(C2O4)3]3-
(ii)[Co(NH3)3Cl3]

Q 6. List various types of isomerism

possible for coordination
compounds, giving an example of
each.
Q.8. Draw the structures of optical Q.9. Draw all the isomers (geometrical and
isomers of: optical) of:
(i) [Cr(C2O4)3]3- (i) [CoCl2(en)2]+
(ii) [PtCl2(en)2]2+ (ii) [Co(NH3)Cl(en)2]2+
(iii) [Co(NH3)2Cl2(en)]+
Q.10. Write all the geometrical Q.11. Aqueous copper sulphate solution
isomers of [Pt(NH3)(Br)(Cl)(py)] and (blue in colour) gives:
how many of these will exhibit optical (i) a green precipitate with aqueous
isomers? potassium fluoride and
(ii) a bright green solution with aqueous
potassium chloride. Explain these
experimental results.
Bonding in Coordination Compounds

Need of Bonding Theories:

Werner's Theory was unable to answer the following questions :
(i) Why only certain elements possess the remarkable property of forming
coordination compounds?
(ii) Why the bonds in coordination compounds have directional properties?
(iii) Why coordination compounds have characteristic magnetic and optical
properties?
VALANCE BOND THEORY (VBT)
Postulates:
❏ The central metal atom/ion provides a definite number of vacant
orbitals[(n-1)d, ns, np and nd] which undergo hybridization to form suitable
geometry of the complex.

❏ The ligands donate their lone pair of electrons into these vacant hybrid
orbitals of the central atom through coordinate bonds.

❏ If inner orbitals are used in hybridization, the complex is called inner orbital or
low spin. If outer orbitals are used the complex is called outer orbital or high
spin.

❏ The metal-ligand bond is formed by the overlap of ligand orbitals containing

lone pairs with the hybrid orbitals of the central atom, leading to covalent
character.
 Note:
❏ Pairing of d electrons of CM occurs in the presence of STRONG LIGAND and
vice versa.
❏ Order of strength: C>N>O>X , where C, N, O & X are donar atom of the ligand

Limitations of VBT:

❏ It involves a number of assumptions.

❏ It does not give quantitative interpretation of magnetic data.
❏ It does not explain the colour exhibited by coordination compounds.
❏ It does not make exact predictions regarding the tetrahedral and square
planar structures of 4-coordinate complexes.
❏ It does not distinguish between weak and strong ligands.
 Prectice session
Q.1. Find out the Hybridisation, Type of complex and Magnetic character of the
following complex through VBT.
1) [Co(NH₃)6]3+
2) [CoF6]3-
3) [NiCl4]2-
4) [Ni(CN)4]2-
5) [MnBr4]2-
6) [Fe(CN)6]4-
7) [FeF6]3-
8) [Co(C2O4)3]3-
Q.2. The spin only magnetic moment of [MnBr4]2- is 5.9 BM. Predict the geometry
of the complex ion ?

Q.3. Aqueous copper sulphate solution (blue in colour) gives:

(i) a green precipitate with aqueous potassium fluoride and
(ii) a bright green solution with aqueous potassium chloride. Explain these
experimental results.
Q.4. What is the coordination entity formed when excess of aqueous KCN is
added to an aqueous solution of copper sulphate? Why is it that no precipitate
of copper sulphide is obtained when H2S(g) is passed through this solution?
CRYSTAL FIELD THEORY (CFT)

● It is an electrostatic model of coordination compounds.

● Central Metal → point positive charge.
● Ligands → point negative charges(Anionic) / dipole (Cationic)
● In the absence of Ligands the five d orbitals are degenerate.
● They split into two sets of orbitals. (Axial and Non axial)
Crystal Field Splitting in Octahedral Coordination entities
Crystal Field Splitting in Tetrahedral Coordination entities
Factors affecting CFSE:
● Oxidation State of CM ● Low spin tetrahedral
● Size of CM complexes are rarely known as
● Strength of Ligand in case of Splitting in
● 3d < 4d < 5d tetrahedral complexes the
● No. of Ligands → ∆t = 4/9 ∆o CFSE is not enough more to
overcome the Pairing Energy.
Important Notes:
Selection of WFL & SFL :
● In case of d4, d5, d6, d7 configuration and 3d series elements, C > N > O >
X series will be followed.
● In case of d1, d2, d3, d8, d9, d10 configuration, no need to check the
strength of ligand.
● In case of 4d, 5d and 6d series elements, all ligands are SFL.

Coordination number -6 :
● All ligands except F and (F & H2O) are SFL for Co3+.
● NH3 is weak ligand for Mn2+ and Fe2+.

Coordination number -4 :

d8 configuration with SFL → dsp2 hybridisation. (Square Planer Geometry)

Other case → sp3 hybridisation. (Tetrahedral Geometry)
Exceptional Complexes:
● [Fe(NH)6]2+ (sp³d²)
● [Mn(NH)6]2+ (sp³d²)
● [Cu(NH)4]2+ (sp³ / dsp² / sp²d)
COLOUR IN COORDINATION COMPOUNDS
d-d transition in coordination compounds:

Complementary colour chart

 Prectice session
Q.1. Explain on the basis of valence bond theory that [Ni(CN) 4]2- ion with square
planar structure is diamagnetic and the [NiCl4]2- ion with tetrahedral geometry is
paramagnetic.
 Q.3. [Fe(H2O)6]3+ is strongly
Q.2. [NiCl4]2- is paramagnetic while paramagnetic whereas [Fe(CN)6]3- is
[Ni(CO)4] is diamagnetic though both weakly paramagnetic. Explain.
are tetrahedral. Why?
Q.4. Explain [Co(NH3l3)6]3+ is an inner Q.5. Predict the number of unpaired
orbital complex whereas [Ni(NH3)6]2+ electrons in the square planar [Pt(CN)4]2-
is an outer orbital complex. ion.
Q.6. The hexaquo manganese(II) ion contains five unpaired electrons, while
the hexacyanoion contains only one unpaired electron. Explain using Crystal
Field Theory.
Q.7. Draw figure to show the splitting Q.8. What is spectrochemical series?
of d orbitals in an octahedral crystal Explain the difference between a weak
field. field ligand and a strong field ligand.
Q 9. What is crystal field splitting energy? Q.10. [Cr(NH3)6]3+ is paramagnetic
How does the magnitude of ∆O decide the while [Ni(CN)4]2- is diamagnetic.
actual configuration of d orbitals in a Explain why?
coordination entity?
Q.11. A solution of [Ni(H2O)6]2+ is green Q.12. [Fe(CN)6]4- and [Fe(H2O)6]2+ are of
but a solution of [Ni(CN)4]2- is colourless. different colours in dilute solutions.
Explain. Why?
Q.13. Write down the IUPAC name for each of the following complexes and
indicate the oxidation state, electronic configuration and coordination number.
Also give stereochemistry and magnetic moment of the complex:
1) K3[Co(C2O4)3]
2) cis-[CrCl2(en)2]Cl
3) (NH4)2[CoF4]
4) [Mn(H2O)6]SO4
5) K[Cr(H2O)2(C2O4)2].3H2O
6) [Co(NH3)5Cl]Cl2
7) [CrCl3(py)3]
8) Cs[FeCl4]
9) K4[Mn(CN)6]
Q.14. Explain the violet colour of the Q.15. What will be the correct order for
complex [Ti(H2O)6]3+ on the basis of the wavelengths of absorption in the
crystal field theory. visible region for the following:
[Ni(NO2)6]4-, [Ni(NH3)6]2+, [Ni(H2O)6]2+
Bonding in Metal Carbonyls
❏ The homoleptic carbonyls (compounds containing carbonyl ligands only) are
formed by most of the transition metals.

❏ The metal-carbon σ bond in metal carbonyls possess both s and p character.

❏ The M–C bond is formed by the donation of lone pair of electrons on the
carbonyl carbon into a vacant orbital of the metal.

❏ The M–C p bond is formed by the donation of a pair of electrons from a filled d
orbital of metal into the vacant antibonding p* orbital of carbon monoxide.
STRUCTURE OF METAL CARBONYLS:
❏ The metal to ligand bonding in metal
Carbonyls creates a synergic effect
which strengthens the bond between
CO and the metal.
Importance and Application Coordination Compounds
❏ Removing Hardness of water: Na2EDTA.
❏ Extraction processes of metals: [Au(CN)2]--
❏ Purification of metals: [Ni(CO)4]
❏ In biological systems:
Vitamin B12(Co) , Chlorophyll(Mg), Hemoglobin (Fe)
❏ As Catalyst:
Rhodium complex, [(Ph3P)3RhCl], a Wilkinson catalyst, is used for the
hydrogenation of alkenes.
❏ In black and white photography:
The developed film is fixed by washing with hypo solution which dissolves
the undecomposed AgBr to form a complex ion, [Ag(S2O3)2]3-.
❏ In Medal field:
EDTA is used in the treatment of lead poisoning.
Cis–platin and related compounds inhibit the growth of tumours.
 Prectice session

Discuss briefly giving an example in each case the role of coordination

compounds in:
(i) biological systems (iii) analytical chemistry
(ii) medicinal chemistry and (iv) extraction/metallurgy of metals.