represents a silvery-white metal with a cubic crystal structure, which belongs
to the group of transition metals. Such elements can take up several oxidation
states, and for the case of nickel, they can be 4, 3, 2, 1, -1 and -2. This
property of the transition metals is due to their ability to “do chemistry” with
their d-orbitals. In this experiment the structural and magnetic properties of
dichlorobis(triphenylphosphine)nickel(II) (NiCl2P(C6H5)32)
were investigated. The compound represents a tetracoordinate Ni(II) complex,
which can exist in two different form, tetrahedral and square planar, which can
both exist simultaneously when in solutions. The structure of the Ni(II)
complex plays a huge role in determining its magnetic properties. When in
tetrahedral form, the complex exhibits paramagnetism, meaning the material is
weakly attracted to an externally applied magnetic field. This phenomena is
caused by the unpaired electrons which reside in the outermost d-orbital of the
metal centre. These electrons can have magnetic moments in all directions and
because of this property, they form induced magnetic field in the direction of
the applied field.

On the other
hand, if the molecule takes up the square planar form, it would have
diamagnetic properties. Such compounds are not attracted by a magnetic field,
since they do not have any unpaired electrons, meaning that the spins of
electrons will align in opposite directions, cancelling out each other’s
magnetic field. The reason behind the difference in magnetic properties depending
on the structure has to do with the energy levels of the d-orbitals in each of
the cases. When the complex adopts the tetrahedral structure, the de orbitals take up a lower energy level, while the dt2 orbitals
– the higher energy level, as shown in Figure 1.1. Since the number of d
electrons in nickel are 8, following Hund’s rule, two are left unpaired which
are responsible for the paramagnetic properties. The d-orbitals of the square
planer structure have a different energy level configuration, since there are
no ligands along the z-axis and electron repulsion is minimized in this region.
This difference in the displacement of the energy levels allows all eight electrons
to form pair, giving the molecule its diamagnetic character.


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