Transcript Magnetic Susceptibility Synthesis of Mn(acac)3

Magnetic Susceptibility
Synthesis of Mn(acac)3
Synthesis 12
Reasons for Determining Number
of Unpaired Electrons
• Related to the oxidation state of the metal.
• Helpful in assigning geometry.
• Information provided about metal-metal
bonding.
• Information provided about the bonding
between the metal and its ligands.
Octahedral Metal Complexes
• Crystal field theory predicts that the five d
orbitals split.
– 3 orbitals of low energy, t2g
– 2 orbitals of high energy, eg
• The energy ‘gap’ between the two sets of
orbitals depends on the ligands.
– I-<Br-<Cl-<F-<OH-<H2O<NH3<NO2<PPh3<CH3-<CN-<CO (the spectrochemical
series)
Octahedral Metal Complexes
• For octahedral complexes that possess between
4 and 7 d electrons, there are two different ways
to distribute the electrons.
– Depends on the energy ‘gap’.
– Illustrate for Fe(H2O)63+ (five electrons).
• High-spin versus low-spin.
– If the energy gap is large enough, all the electrons will
be placed in the t2g (low-spin).
– If the energy gap is small, five electrons will be paired
in each orbital first (low-spin and high-spin).
Obtaining the Mass Susceptibility
• Packing the sample tube
– Page 7 in the instruction manual
• Operating the balance
– Pages 8 and 9 in the instruction manual.
• Calibration of the instrument, CBal
– Use the MKI standard to do this (Sherwood
Scientific printout).
• Obtain the magnetic susceptibility (mass)
of your sample(s)
Magnetic Susceptibility
g 
C Bal  l  (R  R o )
109  m
Mass susceptibility
l = sample length (cm)
m = sample mass (g)
R = reading for tube place sample
Ro = empty tube reading
CBal = balance calibration constant
 M   g  MW
Molar susceptibility
 M   M'   M (metal core electrons )   M (ligands )   M (other )
1
  T  n ( n  2)
8
'
M