Magnetic properties of TM complexes

Question 1

How can you distinguish between high and low spin complexes experimentally

Answer 1

1. Based on the determination of their magnetic properties

Question 2

What are diamagnetic compounds

Answer 2

1. No unpaired electrons
2. Repelled by magnetic fields
3. Very small effect

Question 3

What are paramagnetic compounds

Answer 3

1. One or more unpaired electrons
2. Weakly attracted to a magnetic field
3. Extent of attraction depends on number of unpaired electrons
4. Many compounds of 3d, 4d and 5d elements are paramagnetic

Question 4

How can you distinguish between paramagnetism and diamagnetism

Answer 4

1. Experimentally by the change in the apparent weight of a sample, when the magnetic field is turned on, in a Gouy Balance

Question 5

When is more weight required for a Gouy Balance

Answer 5

1. More unpaired electrons= more weight needed

Question 6

What does the data obtained from a Gouy Balance allow

Answer 6

1. Enables the calculation of the molar susceptibility ChiM of a sample

Question 7

What is ChiM

Answer 7

1. Is a measure of the amount of magnetisation induced per unit volume of sample and is usually expressed in units of cm3mol-1
2. Magnetism is achieved by alignment of the unpaired electron spins

Question 8

How does ChiM relate to ueff

Answer 8

1. Formula that do not need to memorise
2. Enables study of transition metal complexes
3. Ueff is the effective magnetic moment

Question 9

What is uB

Answer 9

1. 9.294 * 10^-24 JT-1

2. Represents the magnetic moment of a single electron orbiting a nucleus

Question 10

What units are used for ueff

Answer 10

1. B.M. units

2. Bohr Magnetons

Question 11

What does a large ueff value mean

Answer 11

1. High levels of paramagnetism and more unpaired electrons

Question 12

What is the spin-only formula

Answer 12

1. 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)
2. uso=root(N(N+2)) B.M.
3. N= number of unpaired electrons

Question 13

Do high spin complexes have a higher or lower uso

Answer 13

1. higher uso

Question 14

Why do you get deviations from the calculated uso and experimental uso

Answer 14

1. Orbital contributions of the magnetic moment

2. Big differences depend on whether or not there is a significant orbital contribution to the magnetic moment

Question 15

Where are orbital contributions more significant

Answer 15

1. 4d and 5d metals than 3d metals
2. For most 3d metal-complexes and some 4d complexes the experimental values lie reasonably close to the spin-only prediction

Question 16

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

Answer 16

1. Jot down uso for N=1,2,3,4,5

2. Relate magnetic moment (uexpt) data to the values you have calculated using uso

Question 17

When is orbital contribution to a magnetic moment maximised

Answer 17

1. When the electronic configuration of the metal has triple orbital degeneracy
2. 3 equal energy electron configurations possible e.g. d1 (octahedral)

Question 18

What else happens when a ground state electron configuration has triple orbital degeneracy

Answer 18

1. The magnetic moment of the associated material also varies with temperature
2. Temperature dependent paramagnetism