CBSE Class 12 Chemistry Coordination Compounds Notes Set B

COORDINATION COMPOUNDS

IMPORTANT POINTS

Definitions with examples

Coordination compounds

The compounds which contain dative bonds between metal atom and surrounding species is called co-ordination compounds.

Examples- K4[Fe(CN)₆]; [ Cu(NH₃)₄]SO₄; Ni(CO)₄

Coordination complex: A structure containing a metal (usually a metal ion) bonded (coordinated) to a group of surrounding

molecules or ions. They retain their identities even when dissolved in water.

Double Salts-

The addition compounds which are stable in solid state but are broken down into individual constituents ions when dissolved in

water eg: mohr’s salt,potash alum etc.

Central metal atom or ion –

the metal ion surrounded by number of ions or molecules.

eg:- K₄[Fe(CN)₆] , Fe²⁺ is central metal ion.

Ligands –

a molecule,ion or group that coordinates to the central metal atom or ion bound in a definite geometrical arrangement in a complex .

e.g.- H₂O, NH₃, CO, CN־ etc.

Types:-

a)Monodentate/Unidentate: Ligands bound to the central metal atom/ion through a single donor atom. e.g.- Cl^-; H₂O ; NH₃; NO₂^-.

b) Bidentate: Ligates through two donor atoms. e.g.- C₂O₄ ^2- (ox); H₂NCH₂CH₂NH₂(en)

c) Polydentate: which ligates through two or more donor atoms present in a single ligand. e.g.- (EDTA)^4-

d) Chelating ligands: Di- or polydentateligands that usestwo or more donor atoms to bind to a single metal ion to form ring- like complexes.  e.g.- (Ox); (edta)

e) Ambidentate ligand: A ligand that can ligate through twodifferent atoms, one at a time. e.g.- NO₂^- ; SCN^-

Coordination number- The number of coordinating units/ligands around the metal ion. The no. of ligand donor atoms to which the metal is directly bonded through sigma bonds only. It is commonly 4 or 6.

Ionisation Isomerism: This form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion. Example: [Co(NH₃)₅Br] SO₄ and [Co(NH₃)₅ SO₄] Br

Linkage Isomerism:Arises due to the presence of ambidentate ligand In the isomerism, a ligand can form linkage with metal through

different atoms. Example: [Co(NH₃)₅ONO]Cl₂ and [Co(NH₃)5NO₂]Cl₂

Solvate isomerism: This is also known as hydrate isomerism if water is involved as a solvent. Compounds that have the same composition, but differ by whether (or) not solvent molecules are present as ligands in the coordination sphere (or) are merely present as free solvent molecules outside the coordination sphere are known as solvateisomers.

Ex: CrCl₃.6H₂O

 

VALENCE BOND THEORY

 

Paramagnetic and octahedral

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