Chapter 10 Coordination Chemistry II:...
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10-4 Angular Overlap 10-5 The Jahn-Teller Effect 10-6 Four- and Six-Coordinate Preferences 10-7 Other Shapes 10-3 Ligand Field Theory 10-2 Theories of Electronic Structure 10-1 Experimental Evidence for Electronic Structures Chapter 10 Coordination Chemistry II: Bonding “Inorganic Chemistry” Third Ed. Gary L. Miessler, Donald A. Tarr, 2004, Pearson Prentice Hall http://en.wikipedia.org/wiki/Expedia
Transcript of Chapter 10 Coordination Chemistry II:...
10-4 Angular Overlap
10-5 The Jahn-Teller Effect
10-6 Four- and Six-Coordinate Preferences
10-7 Other Shapes
10-3 Ligand Field Theory
10-2 Theories of Electronic Structure
10-1 Experimental Evidence for Electronic Structures
Chapter 10 Coordination Chemistry II: Bonding
“Inorganic Chemistry” Third Ed. Gary L. Miessler, Donald A. Tarr, 2004, Pearson Prentice Hallhttp://en.wikipedia.org/wiki/Expedia
Experimental Evidence for Electronic Structures
Coordination Numbers and Molecular Shapes
Electronic SpectraMagnetic SusceptibilityThermodynamic Data
Experimental Evidence for Electronic Structures;Thermodynamic Data
One of the primary goal of a bonding theory is to explain the energy of compound.
The energy is openly not determined directly by experiment.
Thermodynamic measurements of enthalpies and free energies of reaction are used to compare.
Bonding strength → Stability constants(formation constants)
Experimental Evidence for Electronic Structures;Thermodynamic Data
What is the stability constants?
The equilibrium constants for formation of coordination complex.
Experimental Evidence for Electronic Structures;Thermodynamic Data
Stability constants
Thermodynamic values →Prediction of properties, structures
HSAB concepts
Experimental Evidence for Electronic Structures;Thermodynamic Data
HSAB concepts
The gist of this theory is that soft acids react faster and form stronger bonds with soft bases, whereas hard acids react faster and form stronger bonds with hard bases, all other factors being equal.
The classification in the original work was mostly based on equilibrium constants for reaction of two Lewis bases competing for a Lewis acid.
Hard acids and hard bases tend to have:small size high oxidation statelow polarizabilityhigh electronegativityenergy low-lying HOMO (bases) or energy high-lying LUMO(acids).
Experimental Evidence for Electronic Structures;Thermodynamic Data
HSAB concepts
Experimental Evidence for Electronic Structures;Thermodynamic Data
Entropy Effect
Chelating Ligands
en vs methyl amine
Figure in head….
Stability….
Chelate EffectFive or six membered ring
Experimental Evidence for Electronic Structures;Magnetic Susceptibility
The magnetic properties of a coordination compound can provide indirect evidence of the orbital energy level.
Hund’s rule → the max. # of unpaired e-.
Diamagnetic: all e- paried→ repelled by a magnetic field
Paramagnetic: all e- paried→ attracted into a magnetic field
Magnetic Susceptibility: Measuring Magnetism
Experimental Evidence for Electronic Structures;Magnetic Susceptibility
Gouy methodA sample that is to be tested is suspended from a balance between the poles of a magnet. The balance measures the apparent change in the mass of the sample as it is repelled or attracted by the magnetic field.
Magnetic Susceptibility
Experimental Evidence for Electronic Structures;Magnetic Susceptibility
Electron spin → Spin magnetic moment (ms)
Total spin magnetic moment → Spin quantum # S (sum of ms)
Isolated oxygen atom 1s22s2p4
S = +1/2 +1/2 +1/2 -1/2 = 1
Electron spin → Orbital magnetic moment (ml)Total orbital magnetic moment → Orbital quantum # L (sum of ml)
Max. L for the p4
L = +1 +0 -1 +1 = 1
In physics and applied disciplines such as electrical engineering, the magnetic susceptibility is the degree of magnetization of a material in response to an applied magnetic field.
Experimental Evidence for Electronic Structures;Magnetic Susceptibility
The equation for the magnetic moment
Contribution from L is small in first transition series
2.00023 ≈ 2
Two sources of magnetic moment – spin (S) and Angular (L) motions of electrons
Spin quantum number
Angular momentum quantum number
Experimental Evidence for Electronic Structures;Electronic Spectra
Give a direct evidence of orbital energy level
Give an information for geometry of complexes
Theories of Electronic Structure
Valence bond theory
Crystal field theory
Ligand field theory
Angular overlap method
Theories of Electronic Structure;Valence bond theory
Hybridization ideasOctahedral: d2sp3
d orbitals could be 3d or 4d for the first-row transition metals. (hyperligated, hypoligated)
Theories of Electronic Structure;Valence bond theory
Fe(III)Isolated ion; 5 unpaired e-
In Oh compound; 1 or 5 unpaired e-
Co(II)
High spin
Low spin
High spin
Low spin
Theories of Electronic Structure;Crystal field theory
Crystal field theory (CFT) is a model that describes the electronic structure of transition metal compounds, all of which can be considered coordination complexes.
CFT successfully accounts for some magnetic properties, colours, hydration enthalpies, and spinel structures of transition metal complexes, but it does not attempt to describe bonding.
CFT was developed by physicists Hans Bethe and John Hasbrouck van Vleck in the 1930s.
CFT was subsequently combined with molecular orbital theory to form the more realistic and complex ligand field theory (LFT), which delivers insight into the process of chemical bonding in transition metal complexes.
Theories of Electronic Structure;Crystal field theory
Repulsion between d-orbital electrons and ligand electrons→ Splitting of energy levels of d-orbitals
Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
Electrostatic approachIn an Octahedral field of ligand e- pairs; any e-
in them are repelled by the field.Crystal field stabilization energy (CFSE);the actual distribution vs the uniform field.Good for the concept of the repulsion of orbitals by the ligands but no explanation for bonding in coordination complexes.
Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
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Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
Theories of Electronic Structure;Crystal field theory
Why are complexes formed in crystal field theory?Crystal Field Stabilization Energy (CFSE)Or Ligand Field Stabilization Energy (LFSE)→ the stabilization of the d orbitals because of metal-ligand environments
