Question

A ligand can also be regarded as:
A.Lewis acid
B.Bronsted base
C.Lewis base
D.Bronsted acid

Answer 1

Hint: ligands are the type of molecules or ions which are attached to the central metal ion with a coordination bond. Since the metal ion is a cation, it accepts a lone pair of electrons to form a coordinate bond.

Complete step by step answer:
First let us understand what are lewis acids , lewis bases , bronsted acids and bronsted bases .
A Lewis acid can be defined as a compound or an ionic species which can accept a lone pair of electrons from the donor atom. Examples of Lewis acid include hydronium ion, aluminium cation, etc. The Lewis base is just the opposite, as in it donates a lone pair of electrons to the acceptor. Some examples of Lewis bases are ammonia, water, hydroxyl ion etc. therefore the Lewis acid and base theory is based on electron pairs.
Bronsted bases on the other hand, are the bases which can accept protons from a molecule. For example ammonia can accept one proton to form ammonium ion. Similarly, water can accept a proton in order to form hydronium ions. Whereas, bronsted acids are those which releases protons from a molecule, to the acceptor molecule or ion. Example of bronsted acid could be hydrochloric acid, which is a strong acid so it readily releases its proton in the solution.
In coordination chemistry, a ligand can be defined as an ion or molecule (functional group) which binds to the central metal atom or ion in order to form a coordination complex. The bonding with the metal generally involves formal donation of one or more electron pairs of the ligand. Since the ligand donates electron pairs to the metal atom, therefore, we could say it is acting as a Lewis base, as the definition of Lewis base also says that it donates lone pairs of electrons to the acceptor atom or ions.
So the correct option is C.

Note:
The term ligand is derived from the latin word ligare, which means to bind. It was first used by Alfred Stock in 1916 in relation to silicon chemistry.
Ligands can be cations, anions or neutral molecules. Ligands can further be characterized as monodentate, bidentate, tridentate etc. Ligands which are polydentate are also called chelating ligands.