This document discusses half-life for coordination complexes reactions. It describes that the half-life of a substance is the time it takes for its concentration to reduce to half of the initial value. There are two main types of coordination complex reactions: ligand substitution reactions, where one ligand is exchanged for another without changing the metal's oxidation state; and redox reactions, where electrons are transferred between complexes. Ligand substitution reaction rates can be used to determine if a complex is labile or inert based on whether its half-life is less than or greater than one minute. Some metal complexes like [99mTcO4]- have particular half-lives that make them useful in medical applications like imaging.

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2. TOPIC:
HALF-LIFE FOR COORDINATION
COMPLEXES REACTIONS
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BY:
MEHAK SHABBIR
BS-CHEMISTRY

3. Half-Life for Coordination Complexes Reactions
Half-life:
The half-life of a specie is the time it takes for the
concentration of that substance to fall to half of its initial
value.
Types of Coordination complex reactions:
There are 2 types of coordination complexes reactions
1. Ligand substitution reactions
2. Redox reactions
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4. Ligand Substitution Reaction
Ø Ligand substitution involves the exchange of one ligand for an another ligand
with no change in the oxidation state of the central metal atom.
Ø Ligand substitution reactions of complexes is given as
LnMX + Y → LnMY +X
Where,
X is the leaving group and Y is the entering group
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5. Half-life for Ligand Substitution Reactions
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6. Cont...
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7. Cont...
Labile Complexes Inert Complexes
3min>1min 3min 1day
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8. Cont...
Half-life of substitution reactions of the pair of complexes:
t1/2 less than 1min t1/2 greater than 1day
[Fe(H2O)6]3+ [Fe(CN)6]4-
[Co(H2O)6]2+ [Co(NH3)5(H2O)]3+
[Cr(CN)5]4- [Cr(CN)6]3-
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9. Redox Reactions
Ø A common reaction between coordination complexes involving ligands are
electron transfers.
A + B- → A- + B
Ø In electron transfer, an electron moves from one atom to another, changing the
charge on each but leaving the net charge of the system the same.
Ø There are two different mechanisms of electron transfer redox reactions:
1. Inner sphere electron transfer
2. Outer sphere electron transfer
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10. Cont...
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11. Half-Life Of Aqua Complexes
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12. Half-life of Metals In Coordination Complexes
Technetium(Tc):
Ø [99mTcO4]- has half life of 6hrs
Ø 99mTc used in medical therapy in brain, liver, spleen, kidney and thyroid
scanning and for blood flow studies.
Rhenium(Re):
Ø (188ReO4)- has half life of 16.9~17hrs
Ø Rhenium-188 allows synthesizing radiopharmaceuticals for diagnostics and
therapy of malignant tumors, bone metastases and other diseases.
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