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2/9/2015
1
Inorganic Chemistry 2
Bonding in
Coordination Compounds
Alireza Gorjiagorji@yazd.ac.ir
Department of Chemistry, Yazd University
1. Crystal Field Theory CFT
2. Ligand Field Theory LFT
3. Molecular Orbital Theory MOT
Bonding in Coordination Chemistry
پیوند در شیمی کوئوردیناسیون
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1-Crystal Field Theory نظریه میدان بلور
•Assumptions
1. Ligands:
negative point charges
2. Metal-ligand bonding:
entirely ionic
3
1929• Focus:
energies of the d orbitals
agorji@yazd.ac.ir
کدام اوربیتال های فلر مرکزی در برهم کنش مستقیم با لیگاندها در میدان
هشت وجهی است؟
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کدام اوربیتال های فلر
مرکزی در برهم کنش
مستقیم با لیگاندها در
میدان هشت وجهی
است؟
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کدام اوربیتال های فلر مرکزی در برهم کنش مستقیم با لیگاندهادر میدان هشت وجهی است؟
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Strong field Weak field
-4Dq
+6Dq
10Dq 10Dq
Crystal field splitting of d orbital in octahedral field
در میدان هشت وجهیdشکافتگی اوربیتال های
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High spin Low spin
strong-field (low-spin):
large splitting of d orbitals
weak-field (high-spin):
small splitting of d orbitals9agorji@yazd.ac.ir
d1 d2
d3 d4
Placing electrons in d orbitals
Strong field Weak field Strong field Weak field
-4Dq -8Dq
-12Dq -16Dq+p -6Dq10agorji@yazd.ac.ir
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d4
Strong field =
Low spin
(2 unpaired)
Weak field =
High spin
(4 unpaired)
PE < 10Dq PE > 10Dq
5
4
610
a
rZeDq
10Dq
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1 u.e. 1 u.e.
d9
Placing electrons in d orbitals
1 u.e. 5 u.e.
d5
0 u.e. 4 u.e.
d6
1 u.e. 3 u.e.
d7
2 u.e. 2 u.e.
d8
0 u.e. 0 u.e.
d10
-20Dq + 2P 0 -24Dq + 2P -4Dq -8Dq
-12Dq -6Dq 0
-18Dq + P
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Do is the ligand field splitting parameter
E(t2g) = -0.4Do x 3 = -1.2Do
E(eg) = +0.6Do x 2 = +1.2Do
Splitting of d orbitals in an octahedral field
-0.4Do
+0.6Do
2- Ligand Field Theory LFT
تئوری میدان لیگاند
13
J. H. Van Vleck 1935
agorji@yazd.ac.ir
D increases with increasing formal charge on the metal ion
D increases on going down the periodic table
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4
610
a
rZeDq
Do
Do
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Magnetic Properties of Coordination Compounds and Crystal Field Theory
Paramagnetism illustrated:
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Diamagnetic complexes
very small repulsive interaction with
external magnetic field
no unpaired electrons
Paramagnetic complexes
attractive interaction with
external magnetic field
some unpaired electrons
BMnns )2(
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Measured magnetic moments include contributions from both spin and orbital spin. In the
first transition series complexes the orbital contribution is small and usually ignored.
BMnns )2(
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The Visible Spectrum
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Relationship Between Absorbed and Observed Color
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The spectrochemical series
CO, CN- > phen > NO2- > en > NH3 > NCS- > H2O > RCO2
- > OH- > F- > Cl- > Br- > I-
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Effect of Ligands on Colors of Coordination Compounds
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Electronic Spectroscopy
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• I- < Br- < SCN- ~Cl- < F- < OH- ~ ONO- < C2O42- < H2O<
NCS- < EDTA4- < NH3 ~ pyr ~ en < phen < CN- ~ CO
• Mn2+ < Ni2+ < Co2+ < Fe2+ < V 2+ < Fe3+ < Co3+ < Mn3+ <
Mo3+ < Rh3+ < Ru3+ < Pd4+ < Ir3+ < Pt4+
The Spectrochemical Seriesسری اسپکتروشیمیایی
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Enthalpy of Hydration of hexahydrate
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Tdدر میدان چهاروجهیdشکافتگی اوربیتال های
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Dt = -(4/9)Do
Dt
Always weak field (high spin)28agorji@yazd.ac.ir
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Dt = -(4/9)Doمیدان چهاروجهی ضعیف است وکمپلکس های
چهاروجهی همیشه پراسپین است29agorji@yazd.ac.ir
D4hدر میدان لیگاند تتراگنالdشکافتگی اوربیتال های
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D4hمربع در میدان لیگاند مسطحdشکافتگی اوربیتال های
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مسطح مربع همیشه کم اسپین استd8میدان مسطح مربع قوی است وکمپلکس های 32agorji@yazd.ac.ir
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d-Level Splitting
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20_461
E
Free metal ion Complex
dz2
dxy
dxz dyz
dx2 - y2
M z
(b)
Free metal ion Complex
dx2 - y2
dxy
dz2
dxz dyz
M
(a)
x
y
E
Dhمیدان لیگاند خطیدرdشکافتگی اوربیتال های
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The symmetry of metal orbitals in an octahedral environment
s
2- Molecular orbitals for coordination compoundsاوربیتال مولکولی ترکیبات کوئوردیناسیون
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M
z
Metal-ligand s interactions in an octahedral environment
Six ligand orbitals of s symmetry approaching the metal ion along the x,y,z axes
We can build 6 SALC
of s symmetry
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6 SALC of s symmetry
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6 SALC of s symmetry
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Combination of Metal and Ligands SALC’s
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π-bonding
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π-bonding
2 orbitals of π-symmetry
on each ligandWe can build 12 SALC
of π-symmetry
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12 SALC
of π-symmetry
t2g
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t2g
π-donor ligands
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Anti-bonding LUMO(π)
The CN- ligand
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π-acceptor ligands
CN-, CO, PR3, C2H4
ML π-bonding (π-back bonding)
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Strong field Weak field
هر دو در یک دیاگرام
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Spectrochemical Series سری اسپکتروشیمیایی
Purely s ligands: en > NH3
Strong field p acceptors large Dlow spin
Weak field p Donorssmall D
high spin
CO, CN- > phen > en > NH3 > NCS- > H2O > RCO2- > OH- > F- > Cl- > Br- > I-
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Distribution of high- and low-spin complexes of the d-block metal ions:
2nd and 3rd row are all low-spin except for PdF2 and [PdF6]4-
1st row tend to be high-spin except for CN- complexes
Co(III) is big exception – all low-spin except for [CoF6]3-
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داین دو دیاگرام را تصحیح کنی
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The 18 electron rule
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MO of Square Planar Complexes
y
x
z
Most convenient to use a local coordinate system on each ligand with
y pointing in towards the metal. py to be used for s bonding.
z being perpendicular to the molecular plane. pz to be used for p bonding perpendicular to the plane, p^.
x lying in the molecular plane. px to be used for p bonding in the molecular plane, p||.
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Molecular Orbitals of ML4 square planar complexes
a1g
eu
b1g
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ML4 square planar complexes
MO diagram
s-only bonding p- bonding58agorji@yazd.ac.ir
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با استفاده از اطالعات زیر دیاگرام اوربیتال مولکولی کمپلکس های چهاروجهی را رسم کنید
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The Jahn-Teller (J-T) theorem states that in molecules/ ions that have a degenerate ground-state, the molecule/ion will distort to remove the degeneracy.
eg egeg
t2gt2g
d3
t2g
Low-spin Cr(III) – only one
way of filling the eg level – not
degenerate, no J-T distortion
energy
Cu(II) – two ways of filling eg level – it is
degenerate, and has J-T distortion
d9
Cr(III)
Jahn-Teller distortion
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Structural effects of Jahn-Teller distortion
two long axialCu-O bonds= 2.45 Å
[Cu(H2O)6]2+
J-T distortion lengthens axial Cu-O’s[Cr(H2O)6]3+
no J-T distortion
four short in-planeCu-O bonds= 2.00 Å
All six Cr-O bonds equal
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Splitting of the d orbitals by Jahn-Teller distortion
eg
t2g
energy
dxz
dx2-y2
dyz
dxy
dz2
Cu(II) in regular octa-hedral environment
Cu(II) after J-T distortion
2.45 Å2.00 Å
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Z- out Z- in
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d-electron configurations that lead to Jahn-Teller distortion
energy
egeg eg
t2g t2g t2g
d4 high-spin d7 low-spin d9
Cr(II) Co(II) Cu(II)Mn(III) Ni(III) Ag(II)
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تلر قوی-انحراف یان
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Structural effects of Jahn-Teller distortion on [Cu(en)2(H2O)2]2+
long axial Cu-O bonds of 2.60 Å
water
Cu
N
N
N
N
ethylenediamine
Shortin-planeCu-Nbonds of2.03 Å
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Structural effects of Jahn-Teller distortion on [Cu(en)3]2+
Cu
long axial Cu-N
bonds of 2.70 Å
N
N
N
N
N
N
Short in-plane Cu-N
bonds of 2.07 Å
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log K1(en) as a function of no of d-
electrons
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7 8 9 10 11
no of d-electrons
log
K1
(en
).
double-humpedcurve
Ca2+Mn2+
Zn2+
rising baselinedue to ioniccontraction
= CFSE
extrastabiliz-ation dueto J-Tdistortion
Thermodynamic effects of Jahn-Teller distortion
Cu(II)
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تلر در چهاروجهی-انحراف یان
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