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Magnetism - Coggle Diagram
Magnetism
Evans method (NMR)
- paramagnetic materials in NMR we can see their electrons allign with the NMR.
When collecting H1 NMR Data we can meke the following observations:
- lines are considerably broadend for solvent protons
- there is no coupling (splitting) observed. But resonances are comparably sharp
- paramagnetic reagents (aka shift reagents in organic chemistry) disperse proton shifts over a large frequency (ppm) range
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Relating to the equation = " the change in chemical shift of an inter refrence compound in the presence and absence of paramagnetic transtion metal complex is correlated to the magnetic suseptability of the transition metal complex".
spin only formula
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- spin angular momenta gives rise to a magnetic moment & both contribute to paramagnetism. - when the atom/ ion is part of a complex - can be quenched -> basically states that it's only spin that is important.
- All we need to know is the no. of unpaired electron (n) and from there we can work out the magnetic moment.
uB (MB) = Bohr Magneton, a physical constant - uB = eh(bar)/2MeC where e= elementry charge (constant), h(bar) = reduced planks constant, Me = mass of electron (constant), c = speed of light. Ub = 9.27x10 ^(-27) JT-1
- measurment of magnetic momentum usually interpreted in terms of the no. of unpaired electrons.
- can therefore be used to determine between low and high spin states
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2 types of Magnetism
Diamagnetism (induced)
- a magnetic field will induce a current in a material such that the resulting field Opposes the applied field - basically repulsion
- the sample is slightly repelled by the applied field ---> will tend to move out of the magnetic field
- all substrates exhibit this behavior
- for such a substance, the magnetic field inside the sample (B) is slightly less than the applied field
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Gouve Balance
- this is an instrument that is used to measure magnetism
- observed changes by placing the solid between 2 magnets and depending on whether it moves inward or outwards we will have a difference in weight.
- but there is a better method called the Evans Method
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Spin Equilibria
- ions with d4 and d7 configuration in octahedral fields may give high or low spin complexes
- if we choose a field strength close to Cross-over point between high and low spin, and the energy separation between the 2 states is of the order kT, temp will have a marked effect on the position of the high spin-low spin equilibria.
- low spin form = diamagnetic
- high spin form = paramagnetic
Graph drawn below:
Definition: the experimental distinction between high and low spin complexes is based on the determination of their magnetic properties.