Magnetic Properties of Complexes

what is paramagnetism and how do molecules have it.

• The electrons inside a molecule may be regarded as miniature magnets. 

•  when there are unpaired electrons, the magnetic moments will align themselves with an externally applied magnetic field. 

• Para-magnetic complexes are attracted into magnetic fields; the magnitude of the attraction depends on the number of unpaired electrons 

How do we calculate the effective magnetic moment of complexes of first row elements can be calculated by using the following ‘spin-only’ equation.

(n is the number of unpaired electrons)

What are the units of μ_eff

μ_eff is usually expressed in units of Bohr magneton (μ_B), or B_M, the magnetic moment associated with a single electron in the H atom: 

What are two practical consequences regarding weight that is caused by para-magnetism

• When weighed in the absence of an applied field and subsequently in the presence of a magnetic field, paramagnetic substances show: an increase in weight 

• From the weight difference, μeff can be calculated and: the number of unpaired electrons can be determined 

  • can find out whether a complex is high or low spin 

How do we weigh paramagnets

The weighing's are carried out in a Gouy balance: 

• The magnet is an electromagnet 

• Calibrations are carried out against samples of precisely known composition corrected for diamagnetism 

What are Diamagnets

Complexes without unpaired electrons: external magnetic field still disturbs the movement of the electrons around the nuclei

(effect is small) 

What is Ferromagnetism

• Substances that exhibit extremely strong attraction to magnetic fields and can become permanently magnetized

Detail the temperature dependence of magnets

Above the critical temperature, the thermal energy is high enough to prevent alignment.

χ: magnetic susceptibility, degree of magnetisation in response to an applied field