# Why transition elements show tendency to form large number of complexes??

Aug 12, 2017

It is because the transition metals have variable oxidation states.

#### Explanation:

The transition elements span from group 3 to 11.They show variable oxidation states according to the catalyst, reacting element or compound, and the conditions of the reaction they are participating in.Thus, they can form a large number of complex compounds

They also form coordination compounds which have ${d}_{\pi} - {d}_{\pi}$ overlap of orbitals.

Aug 13, 2017

It's because they have $d$ orbitals, which are naturally oriented along all the coordinate axes in ways that are convenient for forming many $\sigma$ bonds and some $\pi$ bonds.

Some examples...

• The ${d}_{{z}^{2}}$ and ${d}_{{x}^{2} - {y}^{2}}$ are useful for $\sigma$ bonding along the coordinate axes.

• The ${d}_{x y}$, ${d}_{x z}$ and ${d}_{y z}$ can be used for $\pi$ bonding on octahedral complexes.

The right-hand side of the diagram illustrates $\pi$ bonding with ethene using a ${d}_{x y}$ orbital, and the left-hand side is a $\sigma$ bond with ethene using a ${d}_{{x}^{2} - {y}^{2}}$ orbital.

This kind of bond is known to rotate at low temperatures, and thus, variable-temperature NMR is useful in identifying such complexes.