Question

The maximum possible denticities of a ligand given below towards a common transition and inner-transition metal ion, respectively are:

(A) 6 and 8
(B) 8 and 6
(C) 8 and 8
(D) 6 and 6

Answer 1

Hint: The term denticity determines the total number of donor atoms in a molecule and on the basis of the property denticity ligands can be classified as monodentate, bidentate, etc. By finding the coordination number of the complex towards a common transition element and inner transition element we could find the maximum possible denticities of the ligand.

Complete step by step solution:
- Let’s start with the concept of coordination compounds .They are the molecules that possess one or multiple metal centers which are bound to ligands. Ligands bind to a transition metal and donate a pair of its electrons to the metal atom, thus creating a metal-ligand bond.
- The term denticity refers to the number of atoms with which a ligand binds to a metal ion. A ligand could be monodentate, bidentate, tridentate, tetradentate, polydentate and multidentate. The monodentate ligand means that it binds through a lone pair on a single atom and a bidentate ligand means that it binds through lone pairs on two different atoms or it could even be tridentate, with three atoms bearing their own lone pairs, tetradentate, and so on.
- The terms, multidentate and polydentate, are two general names for ligands which can bind through more than one atom. Also the words chelating ligand and chelator are general names used to refer to these ligands.
- The coordination number (denticity) of the complex towards a common transition element is 6 and the co-ordination of inner transition element is 8.
- From the above discussions it’s clear that the maximum possible denticities of the given ligand towards inner transition metal ion is 8 and towards transition metal ion is 6.

Therefore the answer is option (A) 6 and 8.

Note: Do not confuse the terms denticity and hapticity. Hapticity denotes exclusively to the ligands where the coordinating atoms are contiguous and is usually represented by the 'eta' ($\eta $) notation whereas the term denticity can be described as the number of atoms with which a ligand binds to a metal ion.