Bidentate Ligands

Co-ordination or complex compound refers to a compound in which a metal atom or ion is coordinated to two or more anions or neutral molecules. In most cases, a coordination compound contains one or more complicated ions. For example, K₄[Fe(CN)₆]⁴⁺ is made up of a complex ion, [Fe(CN)₆]⁴⁺.  A ligand is a chemical or ionic species that becomes directly linked to the central metal atom during complex compound formation. Coordinate bonds connect the ligands to the central atom or central ion. As a result, ligands are sometimes referred to as the coordinating group, molecule, or ion in a complex ion.

Bidentate ligands are substances or anions that can form two coordinate covalent bonds with an atom. There are two donor atoms in a bidentate ligand. This signifies that there are two atoms present that are capable of donating their lone electron pairs. 

What is Ligand? 

1. A ligand is a chemical species that becomes directly linked to the central metal atom or central ion during complex compound formation.
2. Coordinate bonds connect the ligands to the central atom or central ion. As a result, ligands are sometimes referred to as the coordinating group, molecule, or ion in a complex ion.
3. The atom in the ligand that can give the electron pair is referred to as the donor atom or the coordinating atom. In ammonia, for example, nitrogen is the donor atom, whereas, in water, oxygen is the donor atom.
4. To form a complex, electron pairs given by ligands are accommodated in empty orbitals of the central metal atom.

Types of Ligands

One or more donor sites can be detected in a ligand. Ligands can be one of the following categories, depending on the number of donor sites:

1. Monodentate or unidentate ligands
2. Bidentate ligands
3. Polydentate ligands 

A ligand is said to be monodentate if it can only establish one coordinate covalent bond per molecule. If there are two donor sites, the ligand is a bidentate ligand. This classification is described by the denticity of ligands. Because the ligand in a chelate is linked to the central metal atom via two or more donor sites, the ligand is either bidentate or polydentate. The ligand of a chelate is usually cyclic or ring in structure. Chelating agents are another name for these ligands.

Bidentate ligands

Bidentate ligands are substances or anions that can form two coordinate covalent bonds with an atom. When an electron-rich chemical species, such as positively charged metal atoms, offers lone electron pairs to an electron-deficient chemical species, a coordinate covalent connection is formed. A coordination compound is generated when ligands and cations bind in this manner. The coordination centre is the atom to which the ligands are bound. There are two donor atoms in a bidentate ligand. This signifies that there are two atoms present that are capable of donating their lone electron pairs. 

Example of Bidentate ligands 

We know that there are two donor atoms in a bidentate ligand. This signifies that there are two atoms present that are capable of donating their lone electron pairs. 

Bidentate ligands include : 

1,2-iaminoethane (H₂NCH₂CH₂NH₂) also known as, ethylenediamine (en) 

Ethanedioate ion (C₂O₄²⁻ ) also known as oxalate ion (ox).

Similarities Between Bidentate and Ambidentate Ligands

The following are the similarities between the Bidentate Ligands and the Ambidentate Ligands:-

1. Both have two donor atoms.
2. Both contain at least two atoms that have lone electron pairs.

Difference Between Bidentate and Ambidentate Ligands

The following are some primary differences between Bidentate Ligands and Ambidentate Ligands:-

1. Bidentate ligands are molecules having two coordinate covalent bonds that can attach to an atom. While Ambidentate ligands have two donor atoms but can only attach to one atom at a time.

2. Bidentate ligands can create two coordinate covalent bonds simultaneously. whereas, Ambidentate ligands can only make one coordinate covalent bond at once.

1. Bidentate ligands examples: ethylenediamine and oxalate ion

Ambidentate ligands examples: thiocyanate ion and nitrate ion.

Conclusion

It is reasonable to conclude that ligands are the fundamental building blocks of coordination molecules. A chemical ligand in coordination is a molecule or ions that connect with the central metal atom and produce a coordination complex as a result. It functions as an electron-pair donor, whereas the centre atom functions as an electron pair acceptor. Bidentate ligands are substances or anions that can form two coordinate covalent bonds with an atom. The primary distinction between bidentate and ambidentate ligands is that bidentate ligands can create two bonds with a central atom simultaneously, whereas ambidentate ligands can establish two bonds with a central atom but only form one bond at once. The Lewis bases that can contribute their two pairs of electrons to a metal atom are known as bidentate ligands. Bidentate ligands are also referred to as chelating ligands because they may be attached to a metal atom in two different locations.