Why do d block elements form coordination compound?

Coordination compounds are the compounds in which the central transition metal atom is linked to a number of ions or neutral molecules called ligands by donation of lone pairs of electrons by these ligands to the central metal atom to form coordinate bonds e.g., [Ni(CN)₄]^2-.

Transition elements form coordination compounds because of the following reasons:

1. They have small size due to which distance between the nucleus of metal atom and the ligands is less so, strong coordinate bonds are formed between them and a stable coordinate complex is formed.
2. They have large effective nuclear charge.
3. They have greater polarizing power due to large charge /size ratio because of small size and large effective nuclear charge. Because of this property transition metal distorts the electron cloud around the ligands and holds them to a greater extent by sharing their lone pair and forms a stable complex.
4. They have vacant d-orbitals to accept lone pairs of electrons donated by ligands.