Paramagnetic gases

1
Measuring Metal Magnetism
Objectives
--Determine magnetic susceptibility of each
transition metal complex transition metal
complex
--Determine magnetic moment of each metal
--Determine electron configuration of each metal
--Compare high-spin/low-spin to ligand field
strength
2
High-Spin and Low-Spin Electron Configurations
Co(III) 6 valence electrons
3
Magnetic Susceptibility ?
Degree of attraction or repulsion to external
magnetic field
?M molar ?para paramagnetic
?ferro ferromagnetic
? depends on electron spin spin-orbit
coupling magnetic moment alignment
4
Magnetic Moment ?eff
--Resultant of number of unpaired electrons on
each metal
S total spin (1/2 per unpaired e )
g magnetogyric ratio (Landé g-factor, 2)
Substitute
n unpaired e
meff moment in Bohr magnetons (mB) mB 9.27 x
10-24 J / T
5
Spin-Orbit Coupling
--Resultant of electron spin and orbital angular
momentum
Electron spin quantum number ms ?1/2
Magnetic quantum number m 0, ?1, ?2, .? l
For d-orbitals, l 2, so m -2, -1, 0, 1,
2 Gives orientation of orbitals
--Transition metal complexes quenched by
ligands bound to d-orbitals, approaches zero
contribution to ?eff or ?M.
--use ?M depends on ?eff(S.O.)
6
Magnetic Moment Alignment
paramagnetism (disordered spins)
ferromagnetism (co-aligned spins)
antiferromagnetism (anti-aligned spins)
Moderate ?M
Very strong ?M
Weak ?M
7
Diamagnetism
--No unpaired electrons slight repulsion of
paired spins to external magnetic field
?eff 0 ?M 0
Superconducting levitation of a 320 pound sumo
wrestler standing on a 60 kg magnet.
8
Measuring Molecular Magnetism Evans Balance
Sample in vial on block
NdFeB magnett
Balance pan
-0.114g
9
Experimental
--Try not to move holder between runs changes
C --If holder isnt moved before temperature
experiments, no need to re-calculate
C --Ethanol is flammable --In all complexes
MSO4 xH2O, all ligands are oxygen-donors