The document discusses the magnetic properties of materials. Magnetism arises from the spin and orbital angular momentum of electrons. Diamagnetic materials have paired electrons and are weakly repelled by magnetic fields. Paramagnetic materials have unpaired electrons and are weakly attracted to magnetic fields. Magnetic susceptibility measures a material's magnetization in a magnetic field, providing information about its electronic configuration and orbital energies based on paired vs unpaired electrons.

1. Magnetic properties
GD Tuli page 258

2. Course Outlines
Chemistry of d-Block Elements and Coordination Complexes
• Back ground of coordination chemistry → Done
• General chemical and physical properties of transition elements →
Done
• Comparison of the elements of first transition series (3d) with
those of second (4d) and third (5d) series → Done
• Nomenclature and Structure of coordination complexes with
coordination number 2-6 → Done
• Chelates and chelate effect → Done
• Theories of coordination complexes
• Werner's Theory → Done
• Valence Bond Theory (VBT)
• Crystal Field Theory (CFT)
• Molecular Orbital Theory (MOT)
• Sidgwick’s electronic interpretation
of coordination → Done
• Effective atomic number (EAN)
• Jahn-Teller theorem
• Magnetic properties →
Continue
• Spectral properties
• Isomerism
• Stereochemistry
• Stability constants of
coordination complexes

3. Magnetochemistry
• Magnetochemistry is the study of the magnetic properties
of materials.
• By "magnetic properties" we mean not only whether a
material will make a good bar magnet, but whether it will
be attracted or repelled by a magnet.
• Magnetism arises from moving charges, such as an
electric current in a coil of wire.
• Magnetic properties also arise from the spin and orbital
angular momentum of the electrons contained in a
compound.
• In a material which does not have a current present, there
are still magnetic interactions.
• Atoms are made of charged particles (protons and
electrons) which are moving constantly.

4. • The processes which create magnetic fields in an atom
are:
Nuclear spin
• Some nuclei, such as a hydrogen atom, have a net spin
which creates a magnetic field.
Electron spin
• An electron has two intrinsic spin states (similar to a top
spinning) which we call up and down or alpha and beta.
Electron orbital motion
• There is a magnetic field
due to the electron moving
around the nucleus.

5. • Each of these magnetic fields interact with one another
and with external magnetic fields.
• However, some of these interactions are strong and others
are negligible.
• Measurement of interactions with nuclear spins are used
to analyze compounds in nuclear magnetic resonance
(NMR) and electron spin resonance (ESR) spectroscopy.
• In most other situations, interaction with nuclear spins is a
very minor effect.
• Interactions between the intrinsic ( ‫اندرونی‬‫۔‬‫يدائشی‬َ‫پ‬‫۔‬‫تی‬َ‫در‬ُ‫ق‬‫۔‬
‫قيقی‬َ‫ح‬‫۔‬‫ر‬َ‫د‬‫ان‬ ) spin of one electron and the intrinsic spin of
another electron are strongest for very heavy elements
such as the actinides.
• This is called spin-spin coupling.
• For these elements this coupling can shift the electron
orbital energy levels.

6. • The interaction between an electron's intrinsic spin and it's
orbital motion is called spin-orbit coupling.
• Spin-orbit coupling has a significant effect on the energy
levels of the orbitals in many inorganic compounds.
• Macroscopic effects, such as the attraction of a piece of
iron to a bar magnet are primarily due to the number of
unpaired electrons in the compound and their
arrangement.
• The various possible cases are called magnetic states of
matter.

7. Origin of magnetism (Source of magnetism)
• If an electric current which is a flow of electron is allowed
to flow through a wire coiled around core, a field is
produced which behaves as if it were due to a magnet, i.e.
magnetic field is produced.
• Now we know that, according to classical model of an
atom the electron has two types of motion:
i) Orbital motion which is due to the motion of the electron
round the nucleus in an orbit.
• Orbital motion can be compared to the flow of electric
current through a coiled wire.
• The orbital motion, therefore, like an electric current
flowing in a coiled wire, also produces magnetic field or
magnetic moment which is called orbital magnetic moment
or simply orbital moment of the electron.

8. ii) Spin motion which is due to the spinning of the electron round
its own axis.
• This spin motion also produces magnetic field or magnetic
moment which is called spin magnetic moment or simply spin
of the electron.
• These two magnetic moments (i.e. orbital magnetic moment
and spin magnetic moment) make an atom behave like a small
magnet, i.e. it is these two magnetic moments which produce
magnetic properties in substances.
• Now we know that when one magnet is placed in the field of
another magnet, the magnetic field produced by one magnet
will interact with that produced by the other.
• This in other words means that when a substance (which behaves as
a magnet due to orbital and spin motion of its electrons as we have
seen above) is placed between the poles of a magnet, the magnetic
field produced by the orbital and spin motion of the electrons
interacts with the externally applied magnetic field.

9. • It is interesting to note that when the various substances are
placed between the poles of a magnet (i.e. in a magnetic
field), they do not behave in a similar way, i.e. they show
different behaviours which are known as magnetic
behaviours.
• These are classified as diamagnetism, paramagnetism;
ferromagnetism antiferrornagnetism and ferrimagnetism.
• Of these the last three are of rare occrrence and will,
therefore, not be considered in detail.
• On the other hand, paramagnetism and diamagnetism are
of great importance.
• If all of the electrons in an atom are paired up and share
their orbital with another electron, then the total spin in
each orbital is zero and the atom is diamagnetic.
• Diamagnetic atoms are not attracted to a magnetic field,
but rather are slightly repelled.

11. Diamagnetic (all spins are paired)
• Weakly repelled by the external magnetic field.
• These substances have fully-filled orbitals.
• Magnetic moment of an electron with spin in one
direction is cancelled by that of other electron with spin in
opposite direction.
• The compounds are diamagnetic when they contain no
unpaired electrons.
• A diamagnetic compound has all of it's electron spins
paired giving a net spin of zero.
• Diamagnetic compounds are weakly repelled by a
magnet.
"The substances which, when placed in a magnetic field, decrease
the intensity of the magnetic field than in vacuum are called
diamagnetic substances and the property due to which they show
this behaviour is called diamagnetism".

12. • The magnetic lines of force tend to avoid such substances
and as such diamagnetic substances are repelled by the
magnetic field and such substances set themselves at right
angles to the magnetic field (see following figure).
• Examples: TiO2, V2O3, NaCl, benzene, etc.
Figure: Effect of
magnetic field on
diamagnetic
substances.

13. Origin of diamagnetism
• If two electrons with opposite spins are paired in the same
orbital, the magnetic field produced by one electron is
cancelled by that caused by the other electron, because
each of the two electrons has equal and opposite magnetic
moment.
• Thus the substance having only paired electrons give zero
resultant magnetic moment and consequently are
diamagnetic.
• Diamagnetic is temperature-independent and is shown by all types
of substances (even by paramagnetic substances).
• Since diamagnetism is much weaker than paramagnetism (1 to 100
times weaker) and both act opposite to each other, it is difficult for
the substances having unpaired electrons to show diamagnetism, i.e.
the substances having unpaired electrons show a net
paramagnetism.

14. Properties of diamagnetic materials
Some important properties are:
• When suspended in a uniform magnetic field they set
their longest axis at right angles to the field as shown:

15. • In a non-uniform magnetic material, these substances
move from stronger parts of the field to the weaker parts.
• For e.g., when diamagnetic liquid is put in a watch glass
placed on the two pole pieces of an electromagnet and
current is switched on the liquid accumulates on the sides.
[Note on increasing the distance between the pole, the
effect is reversed]
• A diamagnetic liquid in a U shaped tube is depressed,
when subjected to a magnetic field.

16. • The lines of force do not prefer to pass through the
specimen, since the ability of a material to permit the
passage of magnetic lines of force through it is less.
• The substance loses its magnetization as soon as the
magnetizing field is removed.
• Such specimen cannot be easily magnetized and so their
susceptibility is negative.
• Example: Bismuth (-1.4 x 10-6 e.m.u), antimony, copper,
gold, quartz, mercury, water, alcohol, air, hydrogen etc.

17. Paramagnet (Paramagnetism)
• A paramagnetic compound will have some electrons with
unpaired spins.
• Paramagnetic compounds are attracted by a magnet.
"The substances which, when placed in a magnetic field,
allow the magnetic lines of force to pass through them
rather than through vacuum, are called paramagnetic
substances and the property due to which they show this
behaviour is called paramagnetism".
• A paramagnetic substance tends to set itself with its length
parallel to the magnetic field (see following figure).
• Thus a paramagnetic substance is attracted into a
magnetic field.

18. Figure: Effect of magnetic
field on paramagnetic
substances.
Origin of paramagnetism
• Paramagnetism of a substance consisting of atoms, ions or
molecules is caused by the presence of unpaired electrons
in the substance.
• The greater the number of unpaired electrons, the greater
will be paramagnetism shown by the substance.

19. • In substances containing one or more unpaired electrons
the magnetic fields caused by these unpaired electrons are
not mutually cancelled, since each of the unpaired
electrons has equal magnetic moment and thus some
permanent and definite value of resultant magnetic
moment is obtained.
• This resultant magnetic moment which is a combination
of spin and orbital magnetic moments is sufficiently of
high magnitude to overcome the small magnetic moments
induced by the externally applied magnetic field.
• Such a substance, therefore, instead of experiencing
repulsion like diamagnetic substance, experiences
attraction in a magnetic field, i.e. it shows paramagnetic
behaviour.

20. Properties of paramagnetic materials
Some important properties are:
• The paramagnetic substance develops a weak
magnetization in the direction of the field.
• When a paramagnetic rod is suspended freely in a
uniform magnetic field, it aligns itself in the direction of
magnetic field.

21. • As soon as the magnetizing field is removed the
paramagnetics lose their magnetization.
• In a non-uniform magnetic, the specimen move from
weaker parts of the field to the stronger parts (that is it
accumulates in the middle).
• A paramagnetic liquid in U tube placed between two
poles of a magnet is elevated.

22. • The magnetization of paramagnetism decreases with
increase in temperature.
• This is because the thermal motion of the atoms tend to
disturb the alignment of the dipoles.
• Example: Aluminum, platinum, chromium, manganese,
copper sulphate, oxygen etc.,

23. Experiment for determining the magnetic properties of a
sample
• The sample is first weighed in the absence of a magnetic
field (figure a).
• When a field is applied, a diamagnetic sample tends to
move out of the field and thus appears to have a lower
mass (figure b).
• A paramagnetic sample is drawn into the field and thus appears to
gain mass (figure c).
• Paramagnetism is a much stronger effect than is diamagnetism.

24. Why are the substances paramagnetic or diamagnetic?
• It is due to the presence of one or more unpaired electrons
in the molecules (or atoms or ions) of a substance that the
substance shows paramagnetic character.
• Similarly the presence of all the electrons in the paired
state make the substance diamagnetic.
Explanation
• This can be explained as follows:
• We know that an electron is a charged particle and has
orbital motion (i.e., motion of an electron in orbitals) and
spin motion (i.e., spining of the electron about its own
axis).
• Due to these two types of motions, an electron creates a
magnetic field, i.e., each unpaired electron in an atom, an ion
or a moelcule of a substance may be regarded as a
micromagnet which has a definite value of magnetic moment.

25. • If a substance has many unpaired electrons, these
electrons obviously will have the same spin and hence the
magnetic moment of each electron will be equal and in
the same direction.
• Thus the magnetic moment of each unpaired electron will
not be cancelled by the magnetic moment of the other
unpaired electrons present in the substance.
• Consequently if such a substance is placed in the
magnetic field, it experiences attraction and hence shows
paramagnetic character.
• The molecules (or atoms or ions) of a paramagnetic
material has a definite value of magnetic moment.
• Now, consider the case of a substance in which one or
more orbitals contain paired electrons only.

26. • Since the two paired electrons residing in the same orbital
have opposite spins, the spin magnetic moment of one
electron will be equal and opposite to that of the other
electron occupying the same orbital.
• This will result in that the magnetic moment of one
electron will be cancelled by that of the other electron
residing in the same orbital and consequently, if such a
substance is placed in the magnetic field, it experiences
repulsion and hence shows diamagnetic behaviour.
Electronic configuration of Nickel (Ni) is 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d8.

27. Square planar complexes
dsp2 hybridization - square planar
Diamagnetic - No unpaired electrons.

29. • Determine the number of unpaired electrons expected
for [Fe(NO2)6]3− and for [FeF6]3− in terms of crystal
field theory.
• [Fe(NO2)6]3− is a d5 strong-field complex, with the
electrons pairing up in the t2g orbitals.
• The number of unpaired electrons would be one (i.e., t2g).
• The [FeF6]3− is a d5 weak-field complex, and the electrons
will be distributed unpaired throughout the t2g and eg
orbitals (i.e., t2g and eg).
• Therefore, this complex has five unpaired electrons.

31. Magnetic susceptibility
• Just as in the diatomic molecules, the magnetic properties
of a coordination compound can provide indirect evidence
of the orbital energy levels.
• Hund's rule requires the maximum number of unpaired
electrons in energy levels with equal, or nearly equal,
energies.
• Diamagnetic compounds, with all electrons paired, are
slightly repelled by a magnetic field.
• When there are unpaired electrons, the compound is
paramagnetic, and is attracted into a magnetic field.
• The measure of this magnetism is called the magnetic susceptibility.
• Magnetic properties are measured in terms of magnetic moment but
for various substances magnetic moment cannot be measured
directly so we can find first magnetic susceptibility and then it is
converted into magnetic moment.

32. • So, chemically useful information can be obtained by
proper interpretation of the measured values of magnetic
moment.
• Magnetic moment cannot be measured directly but first
find the magnetic susceptibility of a substance then it is
possible to calculate the magnetic moment of a
paramagnetic atom or ion.
Useful information
Ligand nature
• Particular metal oxidation state.
Complex nature
• Paired or unpaired electron.
Definition of magnetic susceptibility
"Magnetic susceptibility is a measure of capacity of a
substance to take up magnetization in a magnetic field".

33. • Greater the magnetization of a substance, greater will be
magnetic susceptibility.
• When a substance is placed in magnetic field of strength
H, the magnetic flux B (i.e. the electromagnetic lines of
force in a region) within a substance is given by:
B = H + 4πI
where
– I = Intensity of magnetization
• Dividing both sides of above equation by H:
B/H = H/H + 4π I/H
where
– B/H = P = Magnetic permeability (means how much
substance is allowed)
– I/H = χv = Magnetic susceptibility per unit volume or
volume susceptibility

34. • Mathematically becomes as:
P = 1 + 4πχv
• The permeability B/H is just the ratio of intensity of lines
of force (magnetic field) within the substance to the
density of such lines.
• Magnetic lines of force greater if paramagnetic substance
present.

35. • This region have its own magnetic flux and if
paramagnetic then density of magnetic lines of force will
be increased.
• In case of diamagnetic substance, the magnetic lines of
force are less.
• If the substance is diamagnetic then density of magnetic
lines of force will be decreased.

36. Atom → Fe
Complex → A B
B.M. → 5.9 4.9
Unpaired electron → 5 4
Oxidation state → +3 +2
In short:
B.M. → Magnetic moment → Magnetic susceptibility →
Oxidation state
Bond type
Stereochemistry
Elucidation of structure with
the help of magnetic moment

37. Measurement of magnetic susceptibility
• Gouy’s method is used for measuring magnetic
susceptibility
Gouy’s method
• It is based on weighing balance (chemical balance).
Principle
• The apparent weight of a substance in air is greatest in the
presence of applied magnetic field than its weight in the
absence of applied magnetic field.
• The difference in weights denotes the force "f” acting on
sample to draw it into field.
• This force can be related to volume susceptibility.
• If greater the weight of substance, greater it will be
attracted by magnetic field.
• So paramagnetic substances have greater weight.

38. Parts of Gouy’s balance
– Electromagnet
– Sensitive balance
– Glass tube
• Magnetic property depends on glass tube.
• If sample is uniformly placed then we get better results.
Working of Gouy’s balance
• The specimen (pure substance-substance whose magnetic
property to be find) in the form of solution, liquid or
powder solid (finally divided solid) is filled in the tube to
known volume (particular volume).
• This tube is supplied in such a way that lower end of
sample is in the center of magnetic poles where a fairly
uniform and constant magnetic field is maintained.

39. • When a magnetic field (H) is applied to sample, it is
either attracted or repelled by magnet and its weight is
apparently changed (i.e. the tube becomes heavier if the
substance is paramagnetic or lighter if it is diamagnetic).
• The force of attraction or repulsion experienced by a
sample can be counter balance with the weight in the
other pan of balance.
• This force can be given by the following expression:
f = 1/2 χvA (H²-Ho²)
Where:
– f = Force acting on the sample
– χv = Volume susceptibility
– A = Cross-sectional area of tube (sample tube)
– Ho = Magnetic field at end of poles which is negligible
– H = Magnetic field at center

40. • If Ho is neglected then expression becomes:
f = 1/2 χvAH²
• This force is counter balance by an apparent change in balance.
• Greater force in case of paramagnetic and greater weight
changes as:
f = ΔW . g
Where
– ΔW = Change in weight
– g = Gravitational force
• By comparing these two equations:
1/2 χvAH² = ΔW . g
• So
H² = 2g ΔW / χvA
• These values are comparatively not absolute (so calibration
required here.
• Calibration therefore required so it done by standard sample).
• The strength of applied field H is difficult to measure (not
accurately).

42. Measurement of susceptibility of paramagnetic solids
• In the Gouy’s method of susceptibility measurement, the
solid sample in the form of a long cylinder (area of cross
section A) is hung from the pan of a balance and is placed
such that one end of the sample is between the pole-pieces
of the magnet (field H ) and the other one is outside the
field.
• The force exerted on the sample by the inhomogeneous
magnetic field is obtained by measuring the apparent
change in the mass of the sample.
• If the sample is in the form of powder, it is filled in a long
nonmagnetic tube which is then suspended from the pan
of the balance.

43. Calibration process
• The calibration done as below:
H² = 2g . ΔW / χvA
H = Strength of applied magnetic field (can not be directly
measure).
• It is difficult to measure applied magnet field accurately.
• In order to overcome this difficulty, the magnetic balance
is first calibrated with a standard compound whose
susceptibility is accurately known and then used for
unknown sample.
• The susceptibility of sample (unknown substance) may be
obtained by comparing force of attraction (in terms of
weight changes) in standard and unknown sample.
Relationship for standard
H² = 2g . (ΔW)S / χsA
S = Stand for standard

44. Relationship for sample
H² = 2g . (ΔW)x / χxA
x = Sample (unknown) substance
• Since magnetic field remains constant during these
measurements and the same tube has been used for the
two samples.
• Hence, by comparing above both equations:
2g . (ΔW)S / χsA = 2g . (ΔW)x / χxA
• Finally we get
χx = χs(ΔW)x / (ΔW)s
χs = Volume susceptibility of standard sample
ΔW = Weight changes find by balance
• This relationship enables us to calculate volume
susceptibility of unknown sample by recording weight
changes for celebrants (used as standard) and sample in
magnetic field.

45. • This relationship holds good if the sample and standard
are filled in the same volume, same glass tube and placed
in fairly uniform and constant field.
• Due to these conditions Gouy’s method should give
relatively good results.
• This method is not absolute method because it is
comparative method as here use known standard sample.

46. Precautions for measurement of magnetic properties by
using Gouy’s method
Sample tube
• The sample tube length (must be 3 to 10 cm) is of Pyrex
glass (quality wise special glass), flat and closed at the
bottom and should have uniform diameter (means same
thickness).
Test substance/sample
• The test substance/ sample is packed in the form of
powder, uniformly in the tube.
Sample should be capped
• The sample tube may be capped to prevent air contents.
Solid standard
• Copper sulphate pentahydrated CuSO4.5H2O or
Hg[Co(NSC)4] mercury (II) tetrathiocyanatocobaltate (II)
can be used as solid standard.

47. Liquid standard
• The liquid sample [nickel chloride NiCl2(aq) first make its
solution] can be used as standard.
Some other standards
Pt
• Pt metal used as standard when use metals.
H2O
• Water also used as standard.
Mohr salt (NH4)2Fe(SO4)2·6H2O
• Mohr salt (double salt) also used for calibration.
Organic solvent
• In organic solvents benzene is used as a solvent.

48. Advantages of Gouy’s method
• Simple apparatus is required.
• Since the amount of sample is quite large even a chemical
balance can measure the weight changes.
• Simple chemical balance may be used rather than
sensitive balance.
Disadvantages of Gouy’s method
• A large amount of sample is required.
• Packing of large tube is crucial for solid samples.

49. The End