MO Diagram for Triangular H - MITweb.mit.edu/5.03/www/readings/hypervalent/hypervalent_sf4.pdf ·...
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Transcript of MO Diagram for Triangular H - MITweb.mit.edu/5.03/www/readings/hypervalent/hypervalent_sf4.pdf ·...
MO Diagram for Triangular H3A fragment approach to deriving molecular orbitals
5.03 Inorganic Chemistry
Image from the H+3 resource center http://h3plus.uiuc.edu/
MO Diagram for Triangular H3A fragment approach to deriving molecular orbitals
5.03 Inorganic Chemistry
HOMO of the Ammonia Molecule
The ammonia HOMO has A1 symmetry
This lone pair orbital also involves bonding of N 2pz with thebonding MO of the stretched H3 molecule
This MO is responsible for the Lewis base character of theammonia molecule
5.03 Inorganic Chemistry
HOMO of the Ammonia Molecule
The ammonia HOMO has A1 symmetry
This lone pair orbital also involves bonding of N 2pz with thebonding MO of the stretched H3 molecule
This MO is responsible for the Lewis base character of theammonia molecule
5.03 Inorganic Chemistry
HOMO of the Ammonia Molecule
The ammonia HOMO has A1 symmetry
This lone pair orbital also involves bonding of N 2pz with thebonding MO of the stretched H3 molecule
This MO is responsible for the Lewis base character of theammonia molecule
5.03 Inorganic Chemistry
HOMO-1 of the Ammonia Molecule
The doubly degenerate ammonia HOMO-1 has E symmetry
This orbital is the bonding interaction between N 2px , 2py andthe E MOs of stretched H3
5.03 Inorganic Chemistry
HOMO-1 of the Ammonia Molecule
The doubly degenerate ammonia HOMO-1 has E symmetry
This orbital is the bonding interaction between N 2px , 2py andthe E MOs of stretched H3
5.03 Inorganic Chemistry
HOMO-3 of the Ammonia Molecule
The singly degenerate ammonia HOMO-3 has A1 symmetry
This orbital is dominated by N 2s character but spreads outand is bonding with the bonding H3 MO
5.03 Inorganic Chemistry
HOMO-3 of the Ammonia Molecule
The singly degenerate ammonia HOMO-3 has A1 symmetry
This orbital is dominated by N 2s character but spreads outand is bonding with the bonding H3 MO
5.03 Inorganic Chemistry
LUMO of the Ammonia Molecule
The singly degenerate ammonia LUMO has A1 symmetry andis N-H σ∗ in character
5.03 Inorganic Chemistry
MO Diagram for the Ammonia Molecule
5.03 Inorganic Chemistry
Summary of Some Key Points
MOs are approximated as LCAOs
The symmetry of the MOs is that of the irreduciblerepresentations
Molecules can be analyzed in terms of constituent fragments,e.g. water as O + “stretched H2”
Bonding is greater when both the orbital energy match andthe spatial overlap is better
The more electronegative atom gets the greater share of thebonding combination and vice versa
Interaction is identically zero between orbitals belonging todifferent irreducible representations
5.03 Inorganic Chemistry
Summary of Some Key Points
MOs are approximated as LCAOs
The symmetry of the MOs is that of the irreduciblerepresentations
Molecules can be analyzed in terms of constituent fragments,e.g. water as O + “stretched H2”
Bonding is greater when both the orbital energy match andthe spatial overlap is better
The more electronegative atom gets the greater share of thebonding combination and vice versa
Interaction is identically zero between orbitals belonging todifferent irreducible representations
5.03 Inorganic Chemistry
Summary of Some Key Points
MOs are approximated as LCAOs
The symmetry of the MOs is that of the irreduciblerepresentations
Molecules can be analyzed in terms of constituent fragments,e.g. water as O + “stretched H2”
Bonding is greater when both the orbital energy match andthe spatial overlap is better
The more electronegative atom gets the greater share of thebonding combination and vice versa
Interaction is identically zero between orbitals belonging todifferent irreducible representations
5.03 Inorganic Chemistry
Summary of Some Key Points
MOs are approximated as LCAOs
The symmetry of the MOs is that of the irreduciblerepresentations
Molecules can be analyzed in terms of constituent fragments,e.g. water as O + “stretched H2”
Bonding is greater when both the orbital energy match andthe spatial overlap is better
The more electronegative atom gets the greater share of thebonding combination and vice versa
Interaction is identically zero between orbitals belonging todifferent irreducible representations
5.03 Inorganic Chemistry
Summary of Some Key Points
MOs are approximated as LCAOs
The symmetry of the MOs is that of the irreduciblerepresentations
Molecules can be analyzed in terms of constituent fragments,e.g. water as O + “stretched H2”
Bonding is greater when both the orbital energy match andthe spatial overlap is better
The more electronegative atom gets the greater share of thebonding combination and vice versa
Interaction is identically zero between orbitals belonging todifferent irreducible representations
5.03 Inorganic Chemistry
Summary of Some Key Points
MOs are approximated as LCAOs
The symmetry of the MOs is that of the irreduciblerepresentations
Molecules can be analyzed in terms of constituent fragments,e.g. water as O + “stretched H2”
Bonding is greater when both the orbital energy match andthe spatial overlap is better
The more electronegative atom gets the greater share of thebonding combination and vice versa
Interaction is identically zero between orbitals belonging todifferent irreducible representations
5.03 Inorganic Chemistry
What are Hypervalent Molecules?
Molecules that appear to violate the octet rule by having morethan eight electrons in the valence shell
Examples: PCl5, SF6, ClF3, I−3To maintain the primacy of 2c-2e bond (Lewis), use of dorbitals were invoked
Alternatively (Pimentel), the 3c-4e bond (MO theory)explains matters
5.03 Inorganic Chemistry
What are Hypervalent Molecules?
Molecules that appear to violate the octet rule by having morethan eight electrons in the valence shell
Examples: PCl5, SF6, ClF3, I−3To maintain the primacy of 2c-2e bond (Lewis), use of dorbitals were invoked
Alternatively (Pimentel), the 3c-4e bond (MO theory)explains matters
5.03 Inorganic Chemistry
What are Hypervalent Molecules?
Molecules that appear to violate the octet rule by having morethan eight electrons in the valence shell
Examples: PCl5, SF6, ClF3, I−3To maintain the primacy of 2c-2e bond (Lewis), use of dorbitals were invoked
Alternatively (Pimentel), the 3c-4e bond (MO theory)explains matters
5.03 Inorganic Chemistry
What are Hypervalent Molecules?
Molecules that appear to violate the octet rule by having morethan eight electrons in the valence shell
Examples: PCl5, SF6, ClF3, I−3To maintain the primacy of 2c-2e bond (Lewis), use of dorbitals were invoked
Alternatively (Pimentel), the 3c-4e bond (MO theory)explains matters
5.03 Inorganic Chemistry
Problematic Lewis Diagram of the SF4 Molecule
S
F
F F
F
5.03 Inorganic Chemistry
Valence Orbital Ionization Energies, eV
Atom 1s 2s 2p 3s 3pH 13.6He 24.6Li 5.4Be 9.3B 14.0 8.3C 19.4 10.6N 25.6 13.2O 32.3 15.8F 40.2 18.6Ne 48.5 21.6S 20.7 11.6
5.03 Inorganic Chemistry
Structure of the SF4 Molecule
5.03 Inorganic Chemistry
Structure of the SF4 Molecule
5.03 Inorganic Chemistry
Structure of the SF4 Molecule
5.03 Inorganic Chemistry
Structure of the SF4 Molecule
5.03 Inorganic Chemistry
Structure of the SF4 Molecule
5.03 Inorganic Chemistry
Electron Density of the SF4 MoleculeAn 0.15 surface contour is plotted (atomic units)
5.03 Inorganic Chemistry
Atomic Charge Distribution in the SF4 MoleculeResults from MO Calculation followed by NBO analysis
S
F
F F
F
Axial S-F bond distances are longer than the equatorial ones
More negative charge is accumulated on the axial F atoms
The analogous SH4 molecule does not exist!
5.03 Inorganic Chemistry
Atomic Charge Distribution in the SF4 MoleculeResults from MO Calculation followed by NBO analysis
S
F
F F
F
Axial S-F bond distances are longer than the equatorial ones
More negative charge is accumulated on the axial F atoms
The analogous SH4 molecule does not exist!
5.03 Inorganic Chemistry
Atomic Charge Distribution in the SF4 MoleculeResults from MO Calculation followed by NBO analysis
S
F
F F
F
Axial S-F bond distances are longer than the equatorial ones
More negative charge is accumulated on the axial F atoms
The analogous SH4 molecule does not exist!
5.03 Inorganic Chemistry
Three-Center Four Electron BondAdvanced by Pimentel and frequently invoked to explain excess of electrons
One of the bonding electron pairs becomes ligand-basednonbonding
This leads to a bond order of 0.5 for both ligands
What is the bond order in SF4?
5.03 Inorganic Chemistry
Three-Center Four Electron BondAdvanced by Pimentel and frequently invoked to explain excess of electrons
One of the bonding electron pairs becomes ligand-basednonbonding
This leads to a bond order of 0.5 for both ligands
What is the bond order in SF4?
5.03 Inorganic Chemistry
Three-Center Four Electron BondAdvanced by Pimentel and frequently invoked to explain excess of electrons
One of the bonding electron pairs becomes ligand-basednonbonding
This leads to a bond order of 0.5 for both ligands
What is the bond order in SF4?
5.03 Inorganic Chemistry
The Sulfur Lone Pair in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
Composition is 67% s, 33% p
5.03 Inorganic Chemistry
The σ Fluorine Lone Pair in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
Composition is 82% s, 18% p
5.03 Inorganic Chemistry
The π Fluorine Lone Pair in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
Composition is 2% s, 98% p
5.03 Inorganic Chemistry
The Axial S–F Bond in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
The axial S-F bond is very polar with some covalent character
The sulfur d contribution to this bonding orbital is only ca. 6%
5.03 Inorganic Chemistry
The Axial S–F Bond in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
The axial S-F bond is very polar with some covalent character
The sulfur d contribution to this bonding orbital is only ca. 6%
5.03 Inorganic Chemistry
D Orbitals for Sulfur?
5.03 Inorganic Chemistry
The Axial S–F Antibond in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
For every two-electron two-center bond formed there is acorresponding antibond
5.03 Inorganic Chemistry
The Equatorial S–F Bond in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
The equatorial S-F bond is less polar than the axial S-F bond
5.03 Inorganic Chemistry
Natural Bond Orders in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
5.03 Inorganic Chemistry
Natural Atomic Valencies in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
The sulfur in SF4 has one lone pair and forms approximately 3bonds, in accord with the octet rule
5.03 Inorganic Chemistry
Natural Atomic Valencies in the SF4 MoleculeNatural Bond Orbital (NBO) analysis following MO calculation
The sulfur in SF4 has one lone pair and forms approximately 3bonds, in accord with the octet rule
5.03 Inorganic Chemistry
Resonance Structures for the SF4 Molecule
5.03 Inorganic Chemistry
Fluoride Ion Abstraction from SF4Neil Bartlett et al.: 10.1021/ic50116a007
SF4(g) + BF3(g) −→ [SF3]+[BF4]
− (s)
5.03 Inorganic Chemistry
Spectra and Structure of the [SF3]+ Ion
Neil Bartlett et al.: 10.1021/ic50116a007
SF4(g) + BF3(g) −→ [SF3]+[BF4]
− (s)
5.03 Inorganic Chemistry
Connecting MO Theory to Lewis Diagrams
Accurate MO calculations provide the total electron densityand predict observable properties (vibrations, NMR, electronictransitions, magnetism)
MOs have the symmetry of the irreducible representationsmaximizing delocalization
LCAO MOs give us the means to calculate the molecularwavefunction and energy levels
The electron density from an MO calculation can beinterpreted in terms of a Lewis picture using NBO analysis
We can recover our powerful Lewis diagrams from accurateMO calculations at an impressive level of detail
5.03 Inorganic Chemistry
Connecting MO Theory to Lewis Diagrams
Accurate MO calculations provide the total electron densityand predict observable properties (vibrations, NMR, electronictransitions, magnetism)
MOs have the symmetry of the irreducible representationsmaximizing delocalization
LCAO MOs give us the means to calculate the molecularwavefunction and energy levels
The electron density from an MO calculation can beinterpreted in terms of a Lewis picture using NBO analysis
We can recover our powerful Lewis diagrams from accurateMO calculations at an impressive level of detail
5.03 Inorganic Chemistry
Connecting MO Theory to Lewis Diagrams
Accurate MO calculations provide the total electron densityand predict observable properties (vibrations, NMR, electronictransitions, magnetism)
MOs have the symmetry of the irreducible representationsmaximizing delocalization
LCAO MOs give us the means to calculate the molecularwavefunction and energy levels
The electron density from an MO calculation can beinterpreted in terms of a Lewis picture using NBO analysis
We can recover our powerful Lewis diagrams from accurateMO calculations at an impressive level of detail
5.03 Inorganic Chemistry
Connecting MO Theory to Lewis Diagrams
Accurate MO calculations provide the total electron densityand predict observable properties (vibrations, NMR, electronictransitions, magnetism)
MOs have the symmetry of the irreducible representationsmaximizing delocalization
LCAO MOs give us the means to calculate the molecularwavefunction and energy levels
The electron density from an MO calculation can beinterpreted in terms of a Lewis picture using NBO analysis
We can recover our powerful Lewis diagrams from accurateMO calculations at an impressive level of detail
5.03 Inorganic Chemistry
Connecting MO Theory to Lewis Diagrams
Accurate MO calculations provide the total electron densityand predict observable properties (vibrations, NMR, electronictransitions, magnetism)
MOs have the symmetry of the irreducible representationsmaximizing delocalization
LCAO MOs give us the means to calculate the molecularwavefunction and energy levels
The electron density from an MO calculation can beinterpreted in terms of a Lewis picture using NBO analysis
We can recover our powerful Lewis diagrams from accurateMO calculations at an impressive level of detail
5.03 Inorganic Chemistry
