Low oxidation states are found when a complex compound has lights capable of -acceptor character in addition to the -bonding . For example in Ni(CO)4 and Fe(CO)5. The oxidation state of nickel and iron is zero.
EXPLANATION:
It means the that ligands which have capacity to accept the electron from the central atom.
Question based on the asked topic:
Actually it is a d-block element and consists of vacant d orbitals which accepts the pair of electrons from the Carbonyl molecules and forms coordinate bond and hence coordination complex of Ni.
Ground state electronic configuration of Ni :
In Ni(CO)4, Ni is in the zero oxidation state i.e., it has a configuration of 3d84s2.
CO is a strong field ligand. Therefore, it causes the pairing of unpaired 3d electrons. Also, it causes the 4s electrons to shift to the 3d orbital, thereby giving rise to sp3 hybridization.
.png)
It means the that ligands which have capacity to accept the electron from the central atom.
Question based on the asked topic:
In [Ni(CO)4] the Oxidation State of Ni is zero then why and how the coordination compound is formed ?
Ni in [Ni(CO)4] is in zero oxidation state. This does not mean that it does not accepts a pair of electrons from ligand and forms coordinate bond.Actually it is a d-block element and consists of vacant d orbitals which accepts the pair of electrons from the Carbonyl molecules and forms coordinate bond and hence coordination complex of Ni.
Ground state electronic configuration of Ni :
In Ni(CO)4, Ni is in the zero oxidation state i.e., it has a configuration of 3d84s2.
CO is a strong field ligand. Therefore, it causes the pairing of unpaired 3d electrons. Also, it causes the 4s electrons to shift to the 3d orbital, thereby giving rise to sp3 hybridization.