Coordination Compounds Class 12 Notes

Coordination Compounds Class 12 Notes

Coordination Compounds


Central Metal Atom
Central Metal atoms/ions are Lewis acids, they can accept pairs of electrons from Lewis bases.

They are Lewis bases - they contain at least one pair of electrons to donate to central metal atom/ion. Ligands are also called complexing agents.

Coordination Sphere
The coordination sphere of a coordination compound or complex consists of the central metal atom or ion plus its attached ligands. The coordination sphere is usually enclosed in square bracket when written in a formula.

Counter Ion
Counter ions are 'simple' cations or anions that may or may not participate in the Coordination.

Coordination Entity
The coordination entity refers to the central metal ion and the ligands attached to it.

The number of donor groups in a single ligand that bind to a central atom in a coordination complex.

A compound containing a ligand bonded to a central metal atom at two or more points.

Symmetrical ligands

Unsymmetrical ligands:

Coordination number:
The coordination number is the number of donor atoms bonded to the central metal atom/ion.

Oxidation number

Homoleptic Compounds
Homoleptic complexes compounds are those coordination compounds in which all the ligand which are connected with central metal atom are same.

HeteroLeptic Compounds
Heteroleptic complexes compounds are those coordination compounds in which all the ligand which are connected with central atom are not same.

hexaamminecobalt (III) chloride

pentaamminechloridocobalt (III) chloride

potassium hexacyanoferrate (III)

potassium trioxalatoferrate (III)

potassium tetrachloridoplatinum (II)

diamminechlorido (methylamine) platinum(II) chloride

Tetraamminediaquacobalt(IlI) chloride

Potassium tetracyanidonickelate(II)

Tris(ethane-1,2-diamine) chromium(III) chloride

[Pt (NH 3) Br Cl (N0 3)]
Amminebromidochloridonitrito-N- platinatc(II) ion

Dichloridobis(ethane-l ,2-diamine) platinum (IV) nitrate



tetrahydroxozincate(II) ion

hexaammineplatinum (IV) ion


tetrabromidocuprate (II)

[CO(NH3)6]2 (SO4)3
hexaaminecobalt(III) sulphate

potassiumtetracyanonicklate (II)





pentaamminenitrito-N-cobalt (III)

[Pt(NH3)2CI (NH2CH3)]Cl
Diammine chlorido (methylamine) platinum (II) chloride

Diammine chlorido (methylamine) platinum (II) chloride

Tetra carbonyl nickel (0)

Hexaaquamanganese (II) ion

Werner’s Theory
Some important postulates of this theory are given below-
# The central metal atoms in coordination compounds show two types of valency. first one is the primary valency (Principal or Ionizable) and the second one is the secondary valency (Auxiliary or non-Ionizable).
# The primary valency relates to the oxidation state and the secondary valency relates to the coordinate number.
# The number of secondary valences is fixed for every metal atom. that means the coordination number is fixed.
# Central metal atom satisfy both its primary and secondary valencies. Primary valency is satisfied by negative ion whereas secondary valancies are satisfied by negative ion or by neutral molecules
# The secondary valancies are always directed towards fixed position in space and this cause definite geometry of the coordinate compound. For examples: If a metal ion has six secondary valencies, these are arranged octahedrally around the central metal ion. If the metal ion has four secondary valencies, these are arranged in either tetrahedral or square planar arrangement around the central metal ion. The secondary valency thus determines the stereochemistry of the complex ion. While the primary valency is non-directional.
# The secondary valencies are generally represented by solid lines while the primary valencies are represented by dashed lines and the ions which satisfy both primary and secondary valencies will be drawn with both solid and dashed lines.
# It could not explain the inability of all elements to form coordination compounds.
# The Werners theory could not explain the directional properties of bonds in various coordination compounds.
# It does not explain the colour, the magnetic and optical properties shown by coordination compounds.


Valence Bond Theory

Crystal Field Theory and Splitting

Magnetic Properties of Coordination Compounds

Colors of Coordination Compounds

Bonding in Metal Carbonyls