Q. Explain about Molecular orbital theory?

Molecular orbital theory is a completely different approach. It starts with identifying the metal orbitals and the ligand orbitals (hybridised) which have the correct symmetry and energies for combination to yield molecular orbitals. The total electrons from the ligands and metal ion are placed into these molecular orbitals and the bond order, which is a measure of the covalency. is determined. Once the energy sequence of molecular orbitals in a complex is known. The properties of the complex can be all explained. It does not start with any assumption regarding the type of bond involved in the complex; rather it comes out as a natural consequence of the theory. Further, it IS much more comprehensive yet the theory has not become very popular. The reason for this is that the quantum mechanical calculations involved are too tedious and many a time cannot be solved. We shall not go into the details of this theory but would like to emphasise that this is the best and comprehensive approach; in all those cases where precise calculations have been possible, the results are in almost 'perfect agreement with the experimental observations.