transition metal complexes...
TRANSCRIPT
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Transition Metal ComplexesBonding
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Bonding Theory
•Crystal Field TheoryCoulomb Interactions–attraction between metal ion and ligand electrons–repulsion between metal electrons and ligand electrons
•Ligand Field TheoryMO TheoryOverlap of orbitals between ligands and metal
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Crystal Field Theory
n+L M
repulsion
attractione-
e-
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Crystal Field Theory
Free M ion andLigands
M andLigands
attraction
repulsion
E
n+L Mrepulsion
attractione-
e-
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Splitting of d Orbitals in Oh Field
o: Ligand Field Splitting Parameter (10 Dq)
More repulsion
Less repulsion
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Factors Affecting the MagnitudeCrystal Field Splitting
•Identity of the ligand•Charge on the metal•Position in a group•Geometry and coordination number
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Absorption Spectrum of [Ti(OH2)6]3+
eg t2g
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Variation of o in Octahedral Ti(III)Complexes
•Ti(III) is a d1 complex and exhibits one absorption inits electronic spectrum due to transition of theelectron from the t2g orbitals to the eg orbitals. Theenergy of the absorption corresponds to o.
Spectrochemical Series:Arrangement of ligandsin order of increasingligand field strength
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Spectrochemical Series•Order of ligand field strength with decreasing o:
acceptor > no effect > weak donor > donorstrong field weak field
CO > CN–> PPh3 > phen ~ NO2–> bipy > en > NH3 ~ py
> CH3CN > NCS- > H2O > C2O42–> OH–> F–> N3
- >NO3
–> Cl–> SCN–> S2- > Br–> I–
•Order of metal with increasing o:Increases with increasing oxidation numberIncreases down a groupMn(II) < Ni(II) < Co(II) < Fe(II) < V(II) < Fe(III) < Co(III) <Mn(IV) < Mo(III) < Rh(III) < Ru(III) < Pd(IV) < Ir(III) <Pt(IV) weak field strong field
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Ligand Field StabilizationEnergy (LFSE)
LFSE = (- 0.4 x + 0.6 y) o
# of electrons
# of electrons
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Strong Field and Weak Field
0.8 o 1.2 o
1.6 o 0.6 o
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Pairing Energy
1.6 o 0.6 o
Pairing Energy:Coulombic repulsion between electrons in the sameorbital
1.6 o –P (pairing energy) > 0.6 o Strong Field1.6 o –P (pairing energy) < 0.6 o Weak Field
Strong FieldLow spin, 2 unpaired electrons
Weak FieldHigh spin, 4 unpaired electrons
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LFSE o and t
0000Zn2+Cu+10
0.410.61Cu2+9
0.821.22Ni2+8
1.230.831.81Co2+7
0.640.442.40Co3+Fe2+6
05052.01Fe3+Mn2+5
0.440.641.62Mn3+Cr2+4
Weak FieldStrong Field
0.831.23V2+Cr3+3
1.220.82V3+2
0.610.41Ti3+1
0000Sc3+Ca2+0
LFSENLFSEN
TetrahedralOctahedralExampledn
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Magnetic Measurements
•Paramagnetic:unpaired electrons
•Diamagnetic:all electrons paired
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Origins of Magnetism•Self spinning
•Spinning about nucleus
Z+e
Origin of OrbitalAngularMomentum
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Spin-only Paramagnetism•Magnetic Moment
= 2{S(S + 1)}1/2 B S = si
= {N(N + 2)}1/2 B
B : Bohr magneton, 9.274 X 10-24 J/T
5.95.925/25Fe3+
4.8 –4.94.9024Mn3+
3.83.873/23Cr3+
2.7 –2.92.8312V3+
1.7 –1.81.731/21Ti3+
Exp.Calc.
/BSNIon
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Thermochemical Correlations
Without LFSE
With LFSE
More Stable
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Tetrahedral Complexes•Only 4 ligands, all weak field
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LFSE o and t
0000Zn2+Cu+10
0.410.61Cu2+9
0.821.22Ni2+8
1.230.831.81Co2+7
0.640.442.40Co3+Fe2+6
05052.01Fe3+Mn2+5
0.440.641.62Mn3+Cr2+4
Weak FieldStrong Field
0.831.23V2+Cr3+3
1.220.82V3+2
0.610.41Ti3+1
0000Sc3+Ca2+0
LFSENLFSEN
TetrahedralOctahedralExampledn
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Tetragonal Complexes
t < 1/2 o
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Square Planar Complexessp > o
sp ~ 1.3 o
d8 Square Planar stable
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Jahn-Teller Effect
•If the ground electronic configuration ofa linear complex is orbitally degenerate,the complex will distort so as to removethe degeneracy and achieve a lowerenergy.
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Ligand FieldTheory
a1g
t1u
eg
t2g
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MO Energy Level Diagram
CFT
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M-L -Bonding
-donor (-base) and -acceptor (-acid)
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Effect of -Interaction on o
0 decreasedWeak Field
0 increasedStrong Field
-donor -acceptor
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M-L -Bonding•Order of ligand field strength with decreasing o:acceptor > no effect > weak donor > donorstrong field weak field
CO > CN–> PPh3 > phen ~ NO2–> bipy > en >
NH3 ~ py > CH3CN > NCS- > H2O > C2O42–> OH–
> F–> N3- > NO3
–> Cl–> SCN–> S2- > Br–> I–
•Low Oxidation State Metal (electron rich)–Acceptor Ligands
•High Oxidation State Metal (electron poor)–Donor Ligands
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PES ofMo(CO)6