Question

Which of the following has flexidentate character ?
A. EDTA
B. en
C. Py
D. Ox

Answer 1

Hint: There are several ligands that have two or more donor atoms. The ligands then can coordinate with metal atoms or ions either through one donor atom forming a non-chelated complex or two donor atoms forming a chelate.

Complete step-by-step answer:
Before proceeding to ligands, let us have an insight on what a coordinate bond is,
A co-ordinate bond can be defined as an alternate covalent bond that is formed by the sharing of electron pairs from a single atom. The same atom is responsible for sharing both the atoms. It is also called dative bond or dipolar bond.
Coordinate covalent bonds are usually formed in reactions that involve two non-metals such as a hydrogen atom or during bond formation between metals ions and ligands.
In coordinate bonds, a ligand is an ion or molecule that connects to a central metal atom to form a coordination complex. The bonding with the metal usually involves a formal donation of one or more of the ligand's electron pairs.
Denticity refers to the number of atoms with which a ligand binds to a metal ion. Now, a ligand can be monodentate, which means it connects through a lone pair in a single atom. A ligand can also be bidentate, meaning it unites through lone pairs on two different atoms. It could even be tridentate, with three atoms bearing their own lone pairs, tetradentate, and so on. The words, polydentate and multidentate, are two general terms for ligands that bind through more than one atom.
Now coming to the question where it has been asked that which has flexidentate character.
As already discussed for a ligand to be flexidentate it should have more than 2 donor sites.
en, Ox(oxalate) are bidentate ligands ,Py is monodentate and hence cannot act as flexidentate ligands. EDTA has many forms, one is hexadentate, pentadentate, so it becomes a flexidentate ligand.
Hence, the correct option is A (EDTA).

Note: A chelate ligand is formed when a polydentate ligand connects itself to the same central metal atom through two or more donor atoms. Denticity thus can be comprehended as the atoms that ligate to the metal ion.