Coordination number of cobalt in ${\left[ {Co{{\left( {{C_2}{O_4}} \right)}_3}} \right]^{3 - }}$ is-
(A) 2
(B) 6
(C) 5
(D) 4

Answer Verified Verified
Hint: The ligand is an ion or molecule (functional group), connected to a central metal atom, which would become a coordinating complex in the field of coordination chemistry. Binding of metals typically implies that one or two electron pairs of a ligand are formally donated.

Complete step by step solution:
The nature of the metal-ligand may range from covalent to ionic. In fact, the order for binding metal-ligand can be around one and three. Ligands are used as Lewis bases, while Lewis acidic "ligands" are considered to exist in unusual situations.
Coordination number, also known as the Ligancy, the number of atoms, ions or molecules retained in or in a crystal by a single atom or ion as its nearest neighbors.
In the given complex the number of coordinated ligand sites is equal. Since in ${\left[ {Co{{\left( {{C_2}{O_4}} \right)}_3}} \right]^{3 - }}$ the ${C_2}O_4^{2 - }$ ligand is present which is a bidentate ligand and the coordinating number is therefore 6.
Bidentate ligands are Lewis bases that contribute electrons to the metal atom by two pairs ("bi").
Bidentate ligands are also labeled chelating ligands, because a metal atom may be "grabbed" in two positions. A chelating ligand compound is called a chelate.

Hence, it is clear that option B is the correct option.

Note: The Latin term ligand implies "to attach or bind." Ligands can be neutral compounds, cations and anions. The ligands serve as Lewis bases (electron pairs) and Lewis acid (electron pair acceptor) central metal atoms. The properties of connecting metal to ligand range from covalent to ionic.