Mechanism coordination chemistry

1. INNER SPHERE
MECHANISM
Sinju
Sureka
Vandita Raj

2. Main characteristics of inner sphere
mechanism.
▪ In order that electron transfer occurs, one of the complexes should be
inert and other one labile.
▪ The inert complex ion should have a ligand capable of bridging both the
complex ions during the formation of intermediate.
▪ Faster than similar reactions occurring through outer sphere mechanism.
▪ Rate of electron transfer increases if the bridging ligand has
unsaturation or extended conjugation in its structure.
▪ Rate increases with increase in nucleophilic character of bridging ligand.
▪ Sometimes along with electron transfer , the bridging ligand is also
transferred from one complex ion to other. But it’s always not necessary.
▪ The transfer or nontransfer of bridging ligand depends upon the relative
stabilities of the products that are possible from the bridged
intermediate.

3. Example 3:
Consider the reaction given below:
(i) [R-C-O-Co (NH3)5]2+ [Cr(H2O)6]2+
oxidant reductant
[(H2O)5Cr-O O-Co(NH3)5]4+
C
R
O
Evidently we can say
that this reaction
follows inner sphere
mechanism. Because
bridging of complex
ion have taken place.
COOR is the bridge
between the oxidant and
the reductant

4. [(H2O)5Cr-O O-Co(NH3)5]4+ hydrolysis [Co(NH3)5(H2O)]2+ +
C [(H2O)5-Cr-O-C-R]2+
R O
Rate of reaction is
increased if R is
unsaturated or
conjugated.
Transfer of
bridging ligand have
taken place.
Reaction is
fast when
compared to
reaction (a)