Nickelrepresents a silvery-white metal with a cubic crystal structure, which belongsto the group of transition metals.
Such elements can take up several oxidationstates, and for the case of nickel, they can be 4, 3, 2, 1, -1 and -2. Thisproperty of the transition metals is due to their ability to “do chemistry” withtheir d-orbitals. In this experiment the structural and magnetic properties ofdichlorobis(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 canboth exist simultaneously when in solutions. The structure of the Ni(II)complex plays a huge role in determining its magnetic properties. When intetrahedral form, the complex exhibits paramagnetism, meaning the material isweakly attracted to an externally applied magnetic field.
This phenomena iscaused by the unpaired electrons which reside in the outermost d-orbital of themetal centre. These electrons can have magnetic moments in all directions andbecause of this property, they form induced magnetic field in the direction ofthe applied field.On the otherhand, if the molecule takes up the square planar form, it would havediamagnetic properties. Such compounds are not attracted by a magnetic field,since they do not have any unpaired electrons, meaning that the spins ofelectrons will align in opposite directions, cancelling out each other’smagnetic field. The reason behind the difference in magnetic properties dependingon the structure has to do with the energy levels of the d-orbitals in each ofthe 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 delectrons in nickel are 8, following Hund’s rule, two are left unpaired whichare responsible for the paramagnetic properties. The d-orbitals of the squareplaner structure have a different energy level configuration, since there areno 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 electronsto form pair, giving the molecule its diamagnetic character.