Nomenclature and Isomerism of
Coordination Compounds
Children's club seminar
Poliraju . K
Introduction
 Coordination chemistry
 Nomenclature of coordination compounds
 Isomerism of coordination compounds
Coordination chemistry
 Complex
Central metal ion bonded via coordinate covalent bonds to
one or more molecules or ions are called ligands.
Complex ion = complex with net charge.
Coordination number = number of covalent bonds formed
between metal ion and the ligands or ligand.
Coordination chemistry
 Coordination compound
(a) Neutral substance made up of complex ion and another
ion of opposite charge.
(b) Neutral complex.
 Ligand
Lewis base – contains at one nonbonding pair of electrons.
Types of complexes
 Cationic complexes
The complex ion has a positive charge.
Example: [Co(NH3)6]3+
 Anionic complexes
The complex carries a negative charge.
Example: [Ag (CN)2] Neutral complex
The complex does not carry a charge.
Example: [Ni(CO)4]
Double salts and coordination compounds
 Those which lose their identity in solution is called double salts
FeSO4(NH4)2SO4. 6H2O  Fe2+ + 2NH4+ + 2SO42- + 6H2O
 Those which retain their identity in solution is called complexes
K4[Fe(CN)6]

4K+ + [Fe(CN)6]4-
Who is Father of Coordination chemistry?
Werner’s theory - 1893
Werner’s Theory
Werner explained the nature of bonding in complexes based on
the two types of valency
Primary valency
The number of charge on the complex ion.
Secondary valency
The number of ligand atoms coordinated to the metal.
This is now called the coordination number.
Coordination chemistry complex formation
reactions
 Mn+ + pLx-
M(L)pn-x
(L = anion)
 Mn+ + pL
M(L)pn+
( L = molecule)
 Where Mn+ = Leiws acid ( center of coordination)
 L and Lx-
=
Leiws bases ( ligands)
Common Ligands
Monodentate ligands
Contains only one donar atom
Examples: H2O, NH3, CN- , SCN- , X- ( halide ions ), CO, O2Bidentate ligands
Contains two donar atoms
Examples: Oxalate ion (ox) C2O42-, etylenediamine (en)
H2NCH2CH2NH2
Polydentate ligands
Contains more than two donar atoms
Example: ethylenediaminetetra acetateion (EDTA4-)
Bidentate ligand
ethylenediamine(en)
oxalate (ox)
Tridentate ligand
diethylenetriamine(dien)
Tetradentate ligand
triethylenetetraamine(trien)
Polydentate ligand (EDTA)
Coordination number : 6
Nomenclature of coordination
compounds : IUPAC rules
Cation named before anion for ionic compounds; When naming
complexes:
 Ligands are named first alphabetically
 Metal atom ion is named last
 Coordination state given in Roman numerals follows in
parentheses
Name of anionic
Change -ide to
Change -ite to
Change -ate to
ligands end with suffix -o
-o
-ito
-ato
Nomenclature : IUPAC rules
Examples for anionic ligands
 Bromide (Br-) becomes bromo
 Chloride (Cl-) becomes chloro
 Hydroxide (OH-) becomes hydroxo
 Oxide (O2-) becomes oxo
 Nitrite (NO2-) becomes nitrito (M-O bond) or nitro (M-N bond)
 Carbonate (CO32-) becomes carbonato
 Thiosulfate (S2O32-) becomes thiosulfato
Nomenclature : IUPAC rules
Neutral ligands referred to by their usual names
Example: ethylenediamine
Exceptions
 Water, H2O = aqua
 Ammonia, NH3 = ammine
 Carbon monoxide, CO = carbonyl
Number of each type of ligand in a complex is indicated by prefix
 di-.2, tri-. 3, tetra-. 4, penta-.5,
If the name of the ligand begins with/ contains a prefix,
 bis-.2, tris-. 3, tetrakis-.4, pentakis-.5, hexakis-.6
Nomenclature : IUPAC rules
If complex is an anion, its name ends with –ate appended to
either the English or Latin name of the metal
Example:
 Scandium, Sc = scandate
 Titanium, Ti = titanate
 Venadium, V = vanadate
 Manganese, Mn = manganate
 Zinc ,
Zn = zincate
Naming coordination compounds
Example 1: [Co (NH3)6]Cl3
i.e . Co3+
Complex ion
= hexaamminecobalt()
Counter ion
= chloride
[Co (NH3)6]Cl3 = hexaamminecobalt()chloride
Formula of coordination
compound
Name of the coordination
compound
K3[Fe(CN)6]
Potassium hexacyanoferrate()
[CoCl(NH3)5]Cl
Pentaamminechlorocobalt()chloride
Na[PtBrCl(NO2)(NH3)]
Sodium amminebromochloronitrito-Nplatinate()
K2[Ni(CN)4]
Potassium tetracyanonickelate()
Fe4[Fe(CN)6]
Iron() hexacyanoferrate()
Metals and chelates in living system
The heme unit in hemoglobin involves a rigid chelating
ligand, H2O or O2 or CO can be the 6th ligand.
Metals and chelates in living system
Chlorophyll, involved in photosynthesis, is a complex ion
of Magnesium(II)ion.
Types of Isomerism
1. Structural Isomerism
a) Coordination isomerism
The interchange of ligands between cationic and anionic
entities of different metal ions present in a complex.
Example : Co(NH3)ClBr Co(NH3)BrCl and [Co(NH3)6][Cr(CN)6]
+
+
-
Br
NH3
NH3
NH3
NH3
Co
NH3
Co
Cl
NH3
NH3
NH3
NH3
Br
NH3
Cl-
b) Ionization isomerism
 The exchange of groups between the complex ion and the ions
outside the complex
 Example: Pt (NH3)4Cl2Br2 and Pt(NH3)4Br2Cl2 produce
different ions in solution
C) Hydrate isomerism :
 It occurs when water forms a part of the coordination entity
or is outside it
 Cr(H2O)6Cl3
 Cr(H2O)5ClCl2.H2O
 Cr(H2O)4Cl2Cl.2H2O
violet
green
dark green
(three ionic chlorines)
(two ionic chlorines)
(one ionic chlorine)
d) Linkage isomerism
 Linkage isomerism arises in a coordination compound containing
ambidentate ligand.
 Example: [Co(NH3)5(NO2)]Cl2
O
O
N
NH3
O
2+
NH3
Co
2+
N
Cl2-
O
NH3
Cl2NH3
Co
NH3
NH3
NH3
NH3
NH3
[Co(NH3)5(NO2)]Cl2 – (Red)
NH3
Co(NH3)5(ONO)]Cl2- (Yellow)
2. Stereoisomerism
a) Geometrical isomerism: cis and trans
 Square planar complex:
Example :
Ma2b2
[Pt(NH3)2Cl2]
Mabcd
[PtBrClNH3(py)]
Geometrical isomerism in Octahedral complex
Ma4b2 type
(cis and trans isomers)
OH2
Cl
OH2
OH2
Cl
Fe
Fe
Cl
OH2
MAA2b2 type - Three isomers ( two cis and one trans)
trans- [CoCl2(en)2]
Cl
OH2
OH2
cis-[CoCl2(en)2]
OH2
OH2
Geometrical isomerism in Octahedral complex
Ma3b3 type
[Co(NH3 )3(NO2 )3
b) Optical isomerism
 Optical isomers are mirror images that cannot be superimposed
on one another.
 The molecules or ions that cannot be superimposed are called
chiral.
Optical Isomerism
20_446
Have opposite effects on plane-polarized light (no superimposable
mirror images)
Polarizing
filter
Tube
containing
sample
Unpolarized
light
Polarized
light
Rotated
polarized light

20_448
Mirror image
of right hand
Left hand
Right hand
20_450
Cl
N
N
Co
N
N
N
N
Co
N
Co
N
cis
N
N
N
Isomer II cannot be
superimposed exactly
on isomer I. They are
not identical structures.
Cl
Cl
Cl
N
Cl
(a)
Cl
N
Cl
trans
The trans isomer and
its mirror image are
identical. They are not
isomers of each other.
Co
Cl
N
Cl
N
N
N
N
Co
Cl
Isomer I N
Isomer II N
(b)
Isomer II has the same
structure as the mirror
image of isomer I.
Optical Isomerism
The absolute configuration be designated Lambda Λ (left-handed)
and Delta Δ (right-handed)
 cis-isomers of octahedral complexes with 2 bidentate ligands and
2 monodentate ligands
 Example : cis-[CoCl2(en)2] complex (cis-bis chel.ates)
Optical Isomerism
Octahedral complexes with 3 bidentate ligands
Example K3[Cr(C2O4)3] complex (tris chelate)