Magnetic properties of TM complexes Flashcards
How can you distinguish between high and low spin complexes experimentally
- Based on the determination of their magnetic properties
What are diamagnetic compounds
- No unpaired electrons
- Repelled by magnetic fields
- Very small effect
What are paramagnetic compounds
- One or more unpaired electrons
- Weakly attracted to a magnetic field
- Extent of attraction depends on number of unpaired electrons
- Many compounds of 3d, 4d and 5d elements are paramagnetic
How can you distinguish between paramagnetism and diamagnetism
- Experimentally by the change in the apparent weight of a sample, when the magnetic field is turned on, in a Gouy Balance
When is more weight required for a Gouy Balance
- More unpaired electrons= more weight needed
What does the data obtained from a Gouy Balance allow
- Enables the calculation of the molar susceptibility ChiM of a sample
What is ChiM
- Is a measure of the amount of magnetisation induced per unit volume of sample and is usually expressed in units of cm3mol-1
- Magnetism is achieved by alignment of the unpaired electron spins
How does ChiM relate to ueff
- Formula that do not need to memorise
- Enables study of transition metal complexes
- Ueff is the effective magnetic moment
What is uB
- 9.294 * 10^-24 JT-1
2. Represents the magnetic moment of a single electron orbiting a nucleus
What units are used for ueff
- B.M. units
2. Bohr Magnetons
What does a large ueff value mean
- High levels of paramagnetism and more unpaired electrons
What is the spin-only formula
- A good approximation of magnetism can be calculated based on the number of unpaired electrons (upes) present in an atom/ion using the spin only formula for magnetic moment (uso)
- uso=root(N(N+2)) B.M.
- N= number of unpaired electrons
Do high spin complexes have a higher or lower uso
- higher uso
Why do you get deviations from the calculated uso and experimental uso
- Orbital contributions of the magnetic moment
2. Big differences depend on whether or not there is a significant orbital contribution to the magnetic moment
Where are orbital contributions more significant
- 4d and 5d metals than 3d metals
- For most 3d metal-complexes and some 4d complexes the experimental values lie reasonably close to the spin-only prediction
How should you approach a problem containing experimental magnetic moment data for a complex, and you need to work out N as part of the solution
- Jot down uso for N=1,2,3,4,5
2. Relate magnetic moment (uexpt) data to the values you have calculated using uso
When is orbital contribution to a magnetic moment maximised
- When the electronic configuration of the metal has triple orbital degeneracy
- 3 equal energy electron configurations possible e.g. d1 (octahedral)
What else happens when a ground state electron configuration has triple orbital degeneracy
- The magnetic moment of the associated material also varies with temperature
- Temperature dependent paramagnetism
