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

x

x

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