# Valence Bond Theory of Coordination Compounds

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Coordination Compound Class 12th– Easy Class 12th chemistry notes Coordination Compound Class 12th

### Valence Bond Theory of Coordination Compounds

According to this theory,

1. Metal-ligand bond is formed by donation of electrons by ligand to metal.
2. Metal atoms or metal ion must have vacant orbitals of equal energies, equal ti the number of ligands to be attached.
3. Sometimes unpaired (n-1)d electrons pair up to create empty orbitals.
4. If no unpaired electrons is present, then complex is diamagnetic. If unpaired electrons are present, complex is paramagnetic.
5. Depending upon the type of hybridisation d2sp3 , dsp2 and sp3 , the shapes of the complex are octahederal, square planar and tetrahedral respectively.

Crystal Field Theory (CFT)– It is more appropriate theory than Valance Bond Theory. According to this theory, metal ligand bonds are ionic in nature, these are formed as a result of interaction of charges on metal ion and ligands. According to this theory, five degenerate d-orbitals get splitted in influence of ligand field, this is known as crystal field splitting.

Spectrochemical series– An arrangement of ligands in order of increasing crystal field strength is spectrochemical series.

${ I }^{ - }<{ Br }^{ - }<{ SCN }^{ - }<{ Cl }^{ - }<{ S }^{ 2- }<{ F }^{ - }<{ OH }^{ - }<{ { C }_{ 2 }{ O }_{ 4 }^{ 2- } }<{ O }^{ 2- }<{ { H }_{ 2 }O }<{ NCS }^{ - }<{ EDTA }^{ 4- }<{ { NH }_{ 3 } }<{ en }<{ NO }_{ 2 }^{ - }<{ CN }^{ - }<{ CO }$

Crystal Field Stabilisation Energy

${CFSE} \propto {Ligand field}$

${ E }\propto \frac { 1 }{ wavelength (\lambda ) }$

Magnetic Property of Coordination Compounds– Coordination compounds having unpaired electrons are paramagnetic whereas the coordination compounds having a paired electrons are diamagnetic.

$Magnetic moment,\quad \mu =\sqrt { n(n+2) } BM$

where, n= number of unpaired electrons

BM= Bohr magneton (unit of magnetic moment)

Organometallic Compounds– Compounds which have atleast one metal-carbon bond are called organometallic compounds.

Metal Carbonyls- Compounds of transition metal with carbonyls (carbon monoxide) are known as metal carbonyls.

Bonding in Metal Carbonyls– Carbonyl compounds are mostly formed by the transition metals. These compounds have well defined structures. These can be joined by metal-metal bonds e.g. [Mn2(CO)10]

Metal-carbon (M—C) σ bond is formed by donation of loan pair of electrons by the carbon atom to the vacant orbital of metal, while M-C π bond is formed by donating lone pair of electron, by the filled d-orbital of metal into the vacant antibonding orbital of ligand, such composition of bonding produce synergic effect.

Chelate Ligand– When a di-or polydentate ligand is bonded through two or more donor sites to a single metal ion is called a chelate ligand.

Chelate Effect– Chelating Ligands form more stable complexes than monodentate analogs. This is called chelate effect.

#### Uses of Coordination Compounds

• In extraction of elements
• In qualitative analysis
• As catalyst
• Biological processess
• Synthesis of coordination compounds

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