inorganic chemistry 2 - yazd
TRANSCRIPT
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Advanced Inorganic Chemistry
Alireza [email protected]
Department of Chemistry, Yazd University
Introduction
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Thermodynamics Kinetics
G = H -T S ‡G = H‡ -T S‡
G° = -RTlnK ‡G= -RTlnk
G
G
Reaction Coordinate
‡G
G
Reaction Coordinate
Large K → yield=100% Large k → fast reaction
Kinetics vs. Thermodynamics
Thermodynamics Kinetics
A
G<0
G
B
A is unstable
ناپايدار
G>0
G
Reaction Coordinate
B
A
A is stable
پايدار
‡G is small
GA is labile
واکنش پذير
A
B
A is inert
بی اثر
‡G is large
G
Reaction Coordinate
A
B
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A is unstable ناپايدار
A
G
Reaction Coordinate
labile
inert
Thermodynamics Kinetics
G / H / S / K ‡ G / ‡ H / ‡ S / k
Stable پايدار
Unstable ناپايدارInert بی اثر
Labile واکنش پذير
nonspontaneous غيرخودبخودی
SpontaneousخودبخودیSlow آهسته
Fast سريع
Acid
Base
Electrophile
Nucleophile
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Reaction Mechanisms
Intimate
Mechanism
Stoichiometry
Mechanism
G
Reaction Coordinate
Stoichiometry Mechanism
Intimate
Mechanism
rds
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Substitution Reaction
MLnX + Y MLnY + X
Stoichiometry Mechanisms
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Stoichiometry Mechanisms in Substitution Reaction
Dissociative InterchangeAssociative
D IA
ML5X + YML5Y + X X=Leaving group
Y=Entering group
D
Dissociative Mechanism in Substitution Reaction
ML5X ML5 + X slow
ML5 + Y ML5Y fast
rate = k1 [ML5X]
k1
k2
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A
Associative Mechanism in Substitution Reaction
ML5X + Y ML5XY slow
ML5XY ML5Y + X fast
k1
k2
rate = k1 [ML5X][Y]
Fast equilibrium
K1 = k1/k-1
k2 << k-1
For [Y] >> [ML5X]
Interchange Mechanism in Substitution Reaction
I
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Intimate Mechanisms in Substitution Reaction
associative activation (a)
dissociative activation (d)
Intimate Mechanisms in Substitution Reaction
d
a
Dd
Aa
Da
a
d
Ad
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da
IdIa
a d
A Aa Ad
D Da Dd
I Ia Id
Mechanisms in Substitution Reactions
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Determination of Stoichiometry Mechanisms
1. Detection of intermediate by fast
spectroscopy and ultrafast spectroscopy.
2. Synthesis and isolation of intermediate.
3. Stereochemistry of reaction.
A & D
Determination of Intimate Mechanisms
Experimental evidence a d
Sensitivity to entering group
Sensitivity to leaving group
trans effect
cis effect
Increasing of steric hindrance on cis ligands - +
Increasing of positive charge on complex + -
S‡ > 0
V‡ > 0
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1- Substitution Reaction in Square Planar Complexes
ML3X + Y ML3Y + X
M = Pt
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rate = k1 [S][PtA3X] + k2[Y][PtA3X]
rate = k1[PtA3X] + k2[Y][PtA3X]
rate = (k1 + k2[Y])[PtA3X]
If [Y] >> [PtA3X] rate = kobs[PtA3X]
kobs = (k1 + k2[Y])
solvent pathway
nucleophile
pathway
rate = k1 [S][PtA3X] + k2[Y][PtA3X]
rate = k1[PtA3X] + k2[Y][PtA3X]
rate = (k1 + k2[Y])[PtA3X]
If [Y] >> [PtA3X] rate = kobs[PtA3X]
kobs = (k1 + k2[Y])
slope = k2
k1
kobs
[Y]
k1 = solvent pathway
k2 = nucleophile pathway
rate law for square planar Pt2+ complexes
k2 nucleophile a
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[PtA2Cl2] + Y [PtA2ClY] + Cl
Y Donor atom
npt
Cl- Cl 3.04
C6H5SH S 4.15
CN- C 7.00
(C6H5)3P P 8.79
CH3OH O 0
I- I 5.42
NH3 N 3.06
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G
Reaction Coordinate
-acceptor-donor
Mechanism of the trans labilization
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trans labilization
Selective synthesis using the trans effect
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ML5X + Y ML5Y + X
2- Substitution Reaction in Octahedral Complexes
Characteristic lifetimes for exchange of water molecules in aqua complexes
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• Labile:
• s-block elements: Large e.g. Na+, K+, Ba2+ etc…
• d-block elements: 1st row, distorted geometries, d10
• f-block
• Inert:
• s-block elements (only a few are relatively ‘inert’); Small e.g. Be2+, Mg2+
• d-block elements: d3 and d6 in Oh high-field, e.g. CrIII, CoIII. Second and third row.
Lability & Inertness
Labile complexes Fast substitution reactions (< few min)
Inert complexes Slow substitution reactions (>h)
a kinetic concept
Inert !
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The Eigen-Wilkins mechanism
ML5X + Y ⇌ ML5X‖Y fast
ML5X‖Y ⇀ ML5Y +X slowk
KE
rate = k[ML5X‖Y]
[ML5X‖Y]= KE[ML5X][Y]
rate = k KE[ML5X][Y]
if [Y]>>[ML5X] [Y]0 ≅ [Y][ML5X]0= [ML5X]+ [ML5X‖Y]= [ML5X](1+ KE[Y])
rate = k KE[ML5X]0[Y]/ (1+ KE[Y])
rate = k KE[ML5X]0[Y] 0/ (1+ KE[Y] 0)
rate = k KE[ML5X]0[Y] 0/ (1+ KE[Y] 0)
k
Id
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Rate is independent of the nature of L
Entering group effects
Rate is dependent on the nature of L
Entering group effects
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The effect of overall charge
[CoL5Cl]2+ + H2O [CoL5OH2]3+ + Cl- k1
[CoLL4Cl]+ + H2O [CoLL4OH2]2+ + Cl- k2
L = amine k1/ k2=1/1000
Activation Energetics
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Octahedral Substitution and ΔV‡
Octahedral Substitution General Rules
