hybridization and hypervalency in transition-metal and...
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Hybridization and hypervalencyin transition-metal and main-group bonding
Martin Kaupp, Winter School on Quantum Chemistry, Helsinki, Dec. 13-17, 2009
(The Absence of) Radial Nodes of Atomic Orbitals,
an Important Aspect in Bonding Throughout the Periodic Table
Consequences for p-Block Elements: Hybridization Defects,
Hypervalency, Bond Polarity, etc….
Consequences für the Transition Metal Elements
Non-VSEPR Structures of d0 Complexes
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Analogy between Wave Functions and Classical Standing Waves
Vibrations of a string fixed at bothends. Base tone and the first twoharmonics are shown.
base tone
1. harmonic
2. harmonic
Note the nodes (zero crossings)!!They result from the necessaryorthogonality of the modes.
x=0 x= Obj100
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The Nodes of the Radial Solutions
R is the product of an exponential e-(1/2) and of an
associated Laguerre polynomial; = 2Zr/na0
1s, 2p, 3d, 4f: no „primogenic repulsion“ (Pekka Pyykkö)
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1s
2p
3d
4f
2p
See also: J. Comput. Chem. 2007, 28, 320.
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2p2p
See also: J. Comput. Chem. 2007, 28, 320.
P-Block Main-Group Elements
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Hybridization Defectsand their Consequencesin p-Block Chemistry
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X-H Binding Energies of Monohydrides XH,and of „Saturated“ Hydrides MHn
W. Kutzelnigg Angew. Chem. 1984, 96, 262.
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W. Kutzelnigg Angew. Chem. 1984, 96, 262.
AO-Energies from Moore Tables
r-expectation values from Desclaux tables (DHF)
20-33% 24-40%
26-55%
10%
Radial Extent and Energies of Valence Orbitals
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Reasons for Hybridization (1)
better bonding overlap
reduced antibonding overlap
(angular)
(radial)
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W. Kutzelnigg, Einführung in die Theoretische Chemie, Vol. 2
Reasons for Hybridization (2)
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Mulliken gross populationsfor valence AOs in XHn hydrideswithout free electron pairs
W. Kutzelnigg Angew. Chem. 1984, 96, 262.
Hybridization Defects (1)
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Hybridization Defects (2)
*A posteriori hybridization analyses from DFT calculations (BP86/TZVP)
cos(180- ) = a2/(1-a2) (a2 = s-character, 1-a2 = p-character)
Holds only for orthogonal hybrids!
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Explanations of the Inert-Pair Effect
1) Promotion energies increase down the group
2) Drago: Binding energies decrease down the group promotion energies are not overcompensated anymore
3) Extension following Kutzelnigg: Promotion does not take place anymore no good hybrids and weakened covalent bonds in higher oxidation state
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Why is Inorganic Lead Chemistry Dominated by PbII, but Organolead Chemistry by PbIV?(J. Am. Chem. Soc. 1993, 115, 1061)
decreasing stability:
R4Pb > R3PbX > R2PbX2 > RPbX3 > PbX4(R = alkyl, aryl; X = halogen, OR, NR2, OOCR, etc……)
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-60
-40
-20
0
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160
PbF4 PbMeF3 PbMe2F2 PbMe3F PbMe4
PbMenF4-n � PbMenF2-n +F2
PbMenF4-n � PbMen-1F3-n +MeF
PbMenF4-nPbMen-2F4-n +C2H6
Ere
act.
(kJ
mol
-1)
Substituent Effects on 1,1-Elimination Reactions of Pb(IV) Compounds
J. Am. Chem. Soc.1993, 115, 1061.
QCISD/DZ+P data
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-60
-40
-20
0
20
40
60
80
100
120
140
160
PbF4 PbMeF3 PbMe2F2 PbMe3F PbMe4
PbMenF4-n→ PbMenF2-n +F2
PbMenF4-n→ PbMen-1F3-n +MeF
PbMenF4-n→ PbMen-2F4-n +C2H6E
reac
t. (
kJ
mol
-1)
Substituent Effects on 1,1-Elimination Reactions of Pb(IV) Compounds
J. Am. Chem. Soc. 1993, 115, 1061.QCISD/DZ+P data
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Hybridization Defects (3)
h(E): NPA/NLMO Hybridization
results from DFT calculations (BP86)
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0.40.60.81.01.21.41.61.82.02.22.42.62.83.0
0.40.60.81.01.21.41.61.82.02.22.42.62.83.0
NP
A A
tomic C
harge on
Pb
p/s
rat
io o
f P
b-X
bon
din
g N
LM
O NPA Charge
Pb-F bond
Pb-C bond
Pb(CH3)4 Pb(CH3)3F Pb(CH3)2F2 Pb(CH3)F3 PbF4
Influence of Electronegative Substituents on Hybridization in PbIV Compounds
J. Am. Chem. Soc. 1993, 115, 1061.
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Bent‘s Rule: Basic Principles
H. A. Bent Chem. Rev. 1961, 61, 275; H. C. Allen at al. J. Am. Chem. Soc. 1958, 80, 2673.exceptions: a) large steric effects, b) very different sizes of substituent orbitals (e.g. H vs. Hg), c) counteracting effects for very light central atoms d) transition metal systems (cf. also Huheey text book)
Obj101
larger angles betweenmore electropositive substituents
more s-character of central atom is directedtowards less electronegative substituent,more p-character to more electronegative substituent
Obj102
Obj103
e.g.:
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Pb
Pb
Pb
Bent‘s rule effects in organolead fluorides
Quasirelativistic ab initio calculations, J. Am.Chem. Soc. 1993, 115, 1061.
102.80
115.50
134.80
101.40
104.10
116.40
101.10
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Bent‘s Rule: Counteracting Effects
negative hyperconjugationcounteracts EN effects
negative hyperconjugation„switched off“
negative hyperconjugationsmall for heavier elements
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Bent‘s Rule and Lone Pairs
h: NPA/NLMO Hybridization
results from DFT calculations (BP86)
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Obj104
Obj105
Obj106
Inversion Barriers and Hybridization
TS
†
pure p-character of LPhigh s-character in bondshigh s-character of LP
high p-character in bonds
everything that enhances hybridization defects increases inversion barrier and decreases angles!
e.g. NH3 << PH3 < AsH3 < SbH3 < BiH3 NLi3 << NH3 << NF3 NH3 << NH2F << NHF2 << NF3
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Further Pecularities of 1st-Row (2. Period) Elements (p-Block)
important: size, electronegativity, hybridization defects
particularly weak bonds for F2, H2O2, N2H4, ..........e.g. BDE (kJ mol 1): F2 155, Cl2 240, Br2 190, I2 149.‑(cf. also low EA of fluorine atom!)explanation: „lone-pair bond weakening effect“ (Sanderson), (less pronounced for heavier homologues)
preference for - multiple bonding compared to chain-linked single bonds
e.g.: O2 vs S8, CO2 vs. SiO2, ketones vs. silicones
e.g. BDE (kJ mol 1):‑
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Binding Energies
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increments ( / , in kJ mol 1):‑
Preference for � -“ multiple bonding compared to chain-linked single bonds
also: bond ionicitycf. silicates, etc…!
234213I
310285Br
381327Cl
565485F
Si-XC-XX
BDEs (kJ mol 1): ‑
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Allred-Rochow
Pauling
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OH3C CH3
Electron-Localisation-FunctionElectron-Localisation-Function
OH3Si SiH3
The Si-O Bond has a Strong Ionic Character
154o111o
Silicon-Oxygen Bonds ElectronegativitySi: 1.74 O: 3.50
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Summary: Hybridization Defects and Related Phenomena in p-Block Main-Group Chemistry
• 2p shell has no primogenic repulsion and is thus compact
• this favors isovalent hybridization in the 2nd period
• electronegative substituents enhance hybridization defects
• for the heavier p-block elements, hybridization defects are important for inert-pair effect, inversion barriers, Bent‘s rule effects, double-bond rule…..
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Hypervalency?On Myth and Reality ofd-Orbital-Participationin Main-Group Chemistry
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On the Definition of Hyper-(co)-Valency
MgF64- SiF62- SF6
covalency increases
ionicity increases
certainly no hypervalency hypervalency ?
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A Working Definition of Hypervalency
We regard a molecule as hypervalent if at least for one atom the bonding situation requires more valence orbitalsthan available for the free atom
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The Early History of Hypervalency, Part 1
electron pair theory, octet ruleLewis 1916; Kossel 1916; Langmuir 1919
directed valency, spmdn hybrids, electroneutrality principle Pauling 1931, 1940, 1948
3-center-4-electron-bondPimentel 1951; Hach, Rundle 1951
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Limiting Bonding Situations: Example of Different Lewis Structures for XeF2
covalent, hypervalent
partially ionic,delocalized
ionicF - Xe2+ F -
F Xe F
F Xe + F -F - Xe+ F
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F Xe + F -F - Xe+ F
3-Center-4-Electron MO Model
a
b
n
a
b
n
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a
b
n
a
b
n
F Xe + F -F - Xe+ F
Modified 3-Center-4-Electron MO Model
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discovery of noble-gas compoundsChernik et al.; Claasen et al.; Bartlett,Hoppe; since 1962:
first ab initio calculations since ca. 1970
first improved wave functions, Mulliken population analyses since ca. 1975:
The Early History of Hypervalency, Part 2
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+ =
The Role of d-Polarization-Functions
p + d polarized p
electric field
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Obj109
weak points of Mulliken population analysis:strong basis-set dependenceunphysical (partly negative) populationsfailure for transition to ionic bonding
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modified Roby/Davidson population analysis
Ahlrichs et al. 1976, 1985;
Wallmeier, Kutzelnigg 1979
„Natural Population Analysis“ (NPA),
„Natural Bond Orbital Analysis“ (NBO)
Reed, Weinhold 1986; Reed, Schleyer 1990
„Natural Resonance Theory“ (NRT)
Weinhold et al., 1995
energy contributions from d-orbitals
Magnusson 1986, 1990, 1993
topological analysis of electron density (QTAIM)
Cioslowski, Mixon 1993
„Generalized Valence Bond“ (GVB) theory
● Hay 1977, Cooper et al. 1994 (full-GVB)
one-center expansion of one-particle density matrix
● Häser 1996
Since late 1990‘s
QTAIM based on experimental densities
(e.g. D. Stalke et al.)
Improved Analyses of Accurate Wave Functions
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“Natural Population Analysis”“Natural Bond Orbital Analysis”Weinhold et al. 1984, 1988
AO basis original basis set
NAO basis “natural atomic orbitals”“natural minimal basis set” (strongly occupied)“natural Rydberg basis set” (sparsely occupied)
NHO basis“natural hybrid orbitals”
NBO basis“natural bond orbitals”NBO-Lewis-structure
NLMO basis
“natural resonance theory” (NRT)superposition of NBO-Lewis structuresWeinhold et al. 1995
occupancy-weighted Löwdin orthogonalization
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- O S2+ O -
O
O 2-
- O S2+ O -O -
O -
- O S O -
O
O
NRT-Analysis of Sulfate Ion
0%
NRT weight:
66.2%
12x1.9% = 22.8%
further ionic structures:11% NRT at HF/6-31G* level
Weinhold et al., 1995
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O
O 2-
- O Cl3+ O -O -
O -
O Cl O -
O
O
Which NRT-Lewis Structure Describes the Perchlorate Ion Best?
0%
NRT weight:
60.9%
12x2.0% = 24.0%
15%
- O Cl3+ O -
further ionic structures: NRT at HF/6-31G* levelWeinhold et al., 1995
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NRT Weights (w) for Various Lewis Structures in Oxo Anions and Sulfur Oxides
NRT at HF/6-31G* (MP2/6-31G*) levelWeinhold et al., 1995
species
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C
C
C
C
CH
H
CC
C
C
H
H
Hyperconjugation Exemplified by Cyclopentadiene
C
H+CC
CC-
H
u3*
C
C
C
C-
CH+
H ......
C
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Negative Hyperconjugation Exemplified by Difluoromethane
......
C
HH
F F(F)
*(C-F)
C
HH
F- F+C
HH
F+ F-C
HH
F F
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Negative Hyperconjugation in F3PO
......
P+F
O-F
F
P+F-
OF
F
P+F
OF
F-
(O)(to e-MO)
*(P-F)(to e*-MO) P
FO
FF
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(M)*(P-F) P
FM
FF
…….and for -backbonding in phosphane complexes…….
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Musher’s Classification of„Hypervalent“ Compounds
(Musher 1969)
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MO-Diagram of SF6
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Summary: Hypervalency, d-Orbital-Participationin p-Block Main-Group Chemistry
• in normal valent and „hypervalent“ p-block main-group systems, d-functions serve as „polarization functions“ but not as true valence orbitals
• hypervalent Lewis structures usually obtain small or no weight!
• ionic bonding contributions dominate, assisted by delocalization (3-c-4-el.-bonding, negative hyperconjugation)
• in PF5, SF6, etc., delocalization is more complex due to s-
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3d
Transition Metal Systems
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r f(
r) in
a.u
.
r in a.u.J. Comput. Chem. 2007, 28, 320
Radial Orbital Densities of the Manganese Atom
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M. Kaupp J. Comput. Chem. 2007, 28, 320. See also: M. A. Buijse, E. J. Baerends J. Chem. Phys. 1990, 93, 4129.
M L
(n-1)s,poutermost core shell
Pauli repulsion stretched bond
(n-1)d
The problem of the outermost core shells in transition-metal atoms
The problem is most pronounced for the 3d elements (nodelessness of the 3d shell)
weak bonds, low-lying excited states, strong (nondynamical) correlation effects
The 4d shell is already better suited for bonding overlap.The 5d shell even more so due to its relativistic expansion.
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M. Kaupp J. Comput. Chem. 2007, 28, 320. See also: M. A. Buijse, E. J. Baerends J. Chem. Phys. 1990, 93, 4129.
The problem is most pronounced for the 3d elements (nodelessness of the 3d shell)
weak bonds, low-lying excited states, strong (nondynamical) correlation effects
The 4d shell is already better suited for bonding overlap.The 5d shell even more so due to its relativistic expansion.
M M
(n-1)s,poutermost core shell
Pauli repulsion stretched bond
(n-1)d
The problem of the outermost core shells in transition-metal atoms
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M. Kaupp J. Comput. Chem. 2007, 28, 320. See also: M. A. Buijse, E. J. Baerends J. Chem. Phys. 1990, 93, 4129.
M L
(n-1)s,poutermost core shell
Pauli repulsion stretched bond
(n-1)d
The problem of the outermost core shells in transition-metal atoms
The problem is most pronounced for the 3d elements (nodelessness of the 3d shell)
weak bonds, low-lying excited states, strong (nondynamical) correlation effects
The 4d shell is already better suited for bonding overlap.The 5d shell even more so due to its relativistic expansion.
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Non-VSEPR Structuresand Bonding for d0-Systems
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Non-VSEPR Structures of d0-Systems
VSEPR = valence-shell electron-pair-repulsion model
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Obj113
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e.g. catalysis
Practical Relevance of d0-Systems
e.g. bioinorganic chemistry
Mo-Cofactor (after Rajagopalan, Johnson)
ZrO2,ferroelectric perovskites
e.g. materials
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1230
Ba
F F
Obj114
MgF F
linearization energies in kJ/mol from SDCI calculations(J. Am. Chem. Soc. 1991, 113, 6012)
The Question of Bendingof the Alkaline Earth
Dihalides
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regular, „VSEPR“ structuresdistorted, „non-VSEPR“ structures
polarization of central-atom semi-core orbitals by the
ligands, „inverse polarization“ of cation
maximization of d-orbital participation in -bonding
mutual repulsion and polarization of the ligands
maximization of -bonding
M
XX
(??)
M2+
X-X- µ>0
X
M
X
Factors Controlling the Structures of d0 Systems
Review:Angew. Chemie 2001, 113, 642.
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Obj117
X
M
b) bent structure
(e.g. SrX2, BaX2)X
d-Orbital-Contributions to HOMO in d0 MX2-Complexes
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Obj119
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BaH2: Electron Localization Function (ELF, color scale) projected on electron density (cloud of points)
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Bending Force Constants (at Linear Structure)for Molecular Alkaline Earth Dihalides
J. Am. Chem. Soc. 1991, 113, 6017
0.9
0.9
CaCl2CaBr2
CaI2
CaF2
MgF2
MgBr2
MgI2MgCl2
BeF2
BeCl2
BeBr2
BeI20.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Ab initio Abwinkelungs-Kraftkonstanten (mdyn/Å)
Abw
inke
lung
s-K
raft
kons
tant
enau
s po
lari
zed
ion
Mod
ell (
mdy
n/Å
)0.9
0.9
CaCl2CaBr2
CaI2
CaF2
MgF2
MgBr2
MgI2MgCl2
BeF2
BeCl2
BeBr2
BeI20.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Ab initio Abwinkelungs-Kraftkonstanten (mdyn/Å)
Abw
inke
lung
s-K
raft
kons
tant
enau
s po
lari
zed
ion
Mod
ell (
mdy
n/Å
)
force constants from polarized ion model too low for Be and Mg complexes but too high for Ca, Sr, and Ba complexes
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0 2 4 6
-0.05
0.00
0.05
0.10
0.15
0.20 r f
(r)
(a.u
.)
r (Å)
5p
5d
6s
6p
Radial Distribution of (Pseudo)-Valence Orbitals of Barium
outer-core polarization and d-orbital participation cannot be separated completely!
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regular, „VSEPR“ structuresdistorted, „non-VSEPR“ structures
polarization of central-atom semi-core orbitals by the
ligands, „inverse polarization“ of cation
maximization of d-orbital participation in -bonding
mutual repulsion and polarization of the ligands
maximization of -bonding
M
XX
(??)
M2+
X-X- µ>0
X
M
X
Factors Controlling the Structures of d0 Systems
Review:Angew. Chemie 2001, 113, 642.
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Low Ligand-Ligand Repulsion for Neutral LigandsJ. Phys. Chem. 1992, 96, 7316
1170
E(MP2)Lin= 0.6 kJ/Mol
Ba2+(H2O)2 Ba
O O
980 E(HF)Plan= 0.4 kJ/Mol
Ba2+(H2O)3Ba
O O
O
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1220
Cs
O O
E(MP2)Lin= 0.2 kJ/Mol
Cs+(H2O)2
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regular, „VSEPR“ structuresdistorted, „non-VSEPR“ structures
polarization of central-atom semi-core orbitals by the
ligands, „inverse polarization“ of cation
maximization of d-orbital participation in -bonding
mutual repulsion and polarization of the ligands
maximization of -bonding
M
XX
(??)
M2+
X-X- µ>0
X
M
X
Factors Controlling the Structures of d0 Systems
Review:Angew. Chemie 2001, 113, 642.
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X: Li BeH BH2 CH3 NH2 OH F0
5
10
15
20
25
30
C2v(in-plane)
C2v(out-of-plane)
CsElin/kJ mol-1
Ba Ba
N N NN
C2v(in-plane)E(HF) = 0.0 kJ mol-1
C2v(out-of-plane) E(HF) = +15.7 kJ mol-1
118.4º 128.8º
Effects of -Bonding
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MR2 (M = Ca, Yb, Eu; R = C[Si(CH3)3]3 )Eaborn et al. Organomet. 1996, 15, 4783.J. Chem. Soc., Chem. Commun. 1997, 1961.
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Sc
Sc
H H
H
F
FF
Structural Preferences of d0 MX3 Complexes
C. A. Jolly, D. S. Marynick Inorg. Chem. 1989, 28, 2893.
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XX
M
XX
XX
‘ip’, ‘b2’
‘op’, ‘a2’
‘op’, a2
‘op’, b1
‘ip’, a1
-Acceptor-Type d-Orbitals for Linear and Bent MX2 d0 Complexes
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180 170 160 150 140 130 120 110 100 905.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
Figure 5
πav
ScF2+
σ
π ip
πop
met
al c
hara
cter
of N
LM
O (i
n %
)
F-Sc-F angle (degs)
-Bonding Favors Bent Structure in some Cases!
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180 170 160 150 140 130 120 110 100 9010111213141516171819202122
Figure 6
πav
ZrO2πop
π ip
σ
met
al c
hara
cter
of N
LM
O (i
n %
)
O-Zr-O angle (degs)
-Bonding Favors Bent Structure in some Cases!
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Inversion of Bent’s rule for d0-Systems
(CH3)2TiCl2
GED data, Haaland et al., 1996.Explanation via -contributions: Chem. Eur. J. 1999, 5, 3632.
Si
CC
ClCl
107.50
114.20
(CH3)2SiCl2
Ti
CC
ClCl
117.30
102.80
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Obj124
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S- S-
H2H2
S- S-
HH
S S
HH
typical ligand types:
Examples for Nonoctahedral Complexes with Sulfur Ligands
See, e.g.: Can. J. Chem. 1989, 67, 1914Inorg. Chem. 1993, 32, 2085Inorg. Chem. 1989, 28, 773, etc.....
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The Structure of W(CH3)6
C3D3
minimumtransition state
+17 kJ/mol CCSD(T)
2.15 Å
2.21 Å
95.60
75.60
2. 18 Å
84.60
WW
M. Kaupp J. Am. Chem. Soc. 1996, 118, 3018.
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Structural Preferences of Hexamethyl Complexes
species: config. structure, ∆Ea
WMe6
MoMe6
CrMe6
d0
d0
d0
C3, 25 (NR: 53)
C3, 39
C3, 12
MMe6- (M=V,Ta)
NbMe6-
d0
d0
D3
(C3, 1)
MMe62- (M=Ti,Zr,Hf) d0 D3
ReMe6+
TcMe6+
d0
d0
C3, 93
C3, 112
ReMe6, TcMe6 d1 D3
OsMe6, RuMe6 d2 D3
aenergy difference between D3 and C3 structure in
kJ/Mol (GGA-DFT level)
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MO Rationalization of Nonoctahedral d0 Structures
S. K. Kang, H. Tang, T. A. Albright J. Am. Chem. Soc. 1993, 115, 1971.
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Landis’ sd-Hybridization Model (1)(J. Am. Chem. Soc. 1998, 120, 1842)
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Landis’ sd-Hybridization Model (2)(J. Am. Chem. Soc. 1998, 120, 1842)
Preferred coordination arrangements for sd5 hybrids.
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Relative energies (kJ mol—1) between D3h and Oh structures of group 6 hexahalide complexes
aDFT-BP86 results, Angew. Chem., Int. Ed. Engl. 2001, 40, 3534. No convergence for CrBr6, CrI6, MoI6.
minimum
transition stateMM
D3h
Oh
Energetics of Baylar Twist for MX6 d0 Complexes
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2.414 Å
88.7º
2.406 Å
83.5º
Mo
SS
S
S S
S
dihedral d = 26º
d / deg
Erel /kJ mol-1
0 5 10 15 20 25 30 35 40 45 50 55 60
0
5
10
15
20
25
30
35
40
Mo(SH)6:intermediate
between octahedraland trigonal prismatic
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Importance of trigonal prismatic intermediates and transition structures of certain molybdenum enzymes
Review: M. Kaupp Angew. Chemie, Int. Ed. Engl. 2004, 43, 546.
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minimumtransition state
+19 kJ/mol BP86/A
2.34 Å
W
The Structure of WCl5CH3
2.22 Å
2.35 Å
C
Cl1
Cs oct. Cs trig. prism
Cl4
Cl3
Cl2
Cl5
79.90
2.35 Å
83.30
85.30
75.6081.10
W
C
Cl1
Cl4
Cl3
Cl2
Cl5
2.33 Å
2.19 Å
2.39 Å
2.35 Å
2.32 Å78.10
102.10
81.90
<Cl1-W-Cl5 = 97.90<Cl1-W-Cl2 = 179.80<Cl3-W-Cl4 = 166.30<Cl1-W-Cl3 = 87.00
BP86 data, relative energies in kJ/molAngew. Chemie 1999, 111, 3219
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The Structure of WCl4(CH3)2
trans oct. C2(min. 0.0)
“intermediate” C2(min. +6.5)
cis oct. C2v(TS +25.7)
cis tp “other face”, C2v(TS +8.5)
tp “same face”, Cs(TS +14.5)
BP86 data, relative energies in kJ/molAngew. Chemie 1999, 111, 3219
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The Structure of WCl3(CH3)3
tp “across” C1(min. 0.0)
tp “same face” C3(min. +2.3)
oct. fac. C3v (TS +61.2)
oct. merid. Cs (TS +26.0)
BP86 data, relative energies in kJ/molAngew. Chemie 1999, 111, 3219
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d(Si-H)=1.488Å, <H-Si-H=120.0º
d(Si-H)=1.563Å, <H-Si-H=93.3º
d(Si-H)=1.500Å, <H-Si-H=110.9º
d(Zr-H)=1.800Å, <H-Zr-H=104.8º
d(Zr-H)=1.902Å, <H-Zr-H=120.0º
d(Zr-H)=1.862Å, <H-Zr-H=116.6º
SiH
HH
+
Zr
HH
H
+
Si
HHH
.
Zr
H HH
.
-
ZrH
HHSi
HH
H
-
Limits of the Isolobal Principle
Review: M. Kaupp Angew. Chemie 2001, 113, 3642.
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Examples of Unsymmetrical Metal Coordination in Oxide Materials
*5d vs. 4d comparisons:KTaO3 is regular octahedral (cubic) and paraelectric, KNbO3 is distorted (rhombohedral) and ferroelectric at lower temperatures.LiTaO3 has a ferroelectric transition at lower temperature (950 K) than LiNbO3 (1480 K).More ionic bonding and larger band gap with 5d vs. 4d, due to relativistic effects!
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J. Am. Chem. Soc. 1993, 115, 11202
Structures of the Dihydride Dimers M2H4 (M = Mg, Ca, Sr, Ba)(relative MP2 Energies in kJ/Mol)
D2h
C3vC2v
C2h
D4h
C2v
0.00.0+20.1+56.0
+507.0+130.4+86.5+33.4
+115.0+5.90.00.0
+19.2+35.5
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Summary: Understanding Non-VSEPR Structures in d0-Complexes
-d0 complexes with purely -bonded ligands tend to violate VSEPR and related models, in spite of increased ligand repulsion.
-while extended VSEPR models are not useful in rationalizing the distorted structures, both MO and VB models are successful for simple homoleptic complexes.
- -bonding is much more important in d0 complexes than in related p-block complexes, due to the avalability of inner d-orbitals.
-the interrelation between -bonding and bond angles is complicated, due to the involvement of different d orbitals.‑
-the “anti-Bent’s-rule” structure of TiCl2(CH3)2 is due to Ti Cl -bonding!‑
-additional -donor ligands influence the angles between -donor ligands in heteroleptic complexes.
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Thank you for your attention!
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MM
C2
C2A
C1
H1H2
H3
Structure of Mo(butadiene)3
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Extreme Resonance Structures for tris(Butadiene)-Molybdenum and Related Complexes
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M M
3 x 3, MoII, d43 x 4, MoIV, d2
(NRT analysis: 3x10%)
Intermediate Resonance Structures for tris(Butadiene)-Molybdenum and Related Complexes
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1
2
3
4
a‘
e‘
a‘‘
e‘‘
e‘
a‘
e‘‘
a‘‘
3e‘
2e‘‘3a‘
2a‘
2e‘
1a‘‘
1e‘‘
1e‘
1a‘
a‘‘,e‘
a‘
a‘,e‘,e‘‘
5p
5s
4d
Mo(C4H6)3 Mo(C4H6)3C3h
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„Non-Berry“ Rearrangement of TaH5
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Trends of the s- and d-valence orbitals in the transition metal seriesa) radial size
from Dirac-Fock calculations (Desclaux)
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Trends of the s- and d-valence orbitals in the transition metal series b) orbital energies
from Dirac-Fock calculations (Desclaux)
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Why??
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Angew. Chem., Int. Ed. Engl. 2001, 40, 3534.
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On the relative energies of 3d- and 4s orbitals
The 3d orbitals are always lower in energy (and smaller!) than 4s.Stronger electron repulsion in 3d may nevertheless favor 4s occupation.
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Ca atom:radial orbital densities
3p orbital (outermost core shell)
3d orbital (valence shell)
Malrieu et al. Chem. Phys. Lett. 1983, 98, 433.