Match the type of ligands given in List-I with appropriate examples given in List-II
|
List-I (Ligands) |
List-II (Examples) |
|
(A). Ambidentate |
(I). thiocyanato |
|
(B). Unidentate |
(II). water |
|
(C). Didentate |
(III). oxalate |
|
(D). Polydentate |
(IV). ethylenediaminetetraacetate |
Choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
Ligands are classified by the number and kind of donor atoms through which they bind the metal: one donor atom (unidentate), two (didentate), several (polydentate), or two different possible donor atoms of which only one binds at a time (ambidentate).
(A) Ambidentate — This matches (I) thiocyanato. The thiocyanate ion can bind through sulphur (M–SCN, thiocyanato-S) or through nitrogen (M–NCS, thiocyanato-N), but only one of them at a time. This is the origin of linkage isomerism.
(B) Unidentate — This matches (II) water. \( \ce{H2O} \) binds through a single lone pair of its oxygen atom, as in \( \ce{[Co(H2O)6]^2+} \).
(C) Didentate — This matches (III) oxalate. \( \ce{C2O4^2-} \) binds through two oxygen atoms and forms a five-membered chelate ring, as in \( \ce{[Fe(C2O4)3]^3-} \).
(D) Polydentate — This matches (IV) ethylenediaminetetraacetate. EDTA4− binds through two nitrogen and four oxygen atoms, so it is a hexadentate ligand.
Shortcut: (A)-(I) appears only in Options (1) and (2), and (B)-(II) then leaves only Option (1).
NCERT (2026-27 edition):
Definitions of Some Important Terms Pertaining to Coordination Compounds – “… When a ligand is bound to a metal ion through a single donor atom, as with Cl–, H2O or NH3, the ligand is said to be unidentate. When a ligand can bind through two donor atoms as in H2NCH2CH2NH2 (ethane-1,2-diamine) or C2O42– (oxalate), the ligand is said to be didentate and when several donor atoms are present in a single ligand as in N(CH2CH2NH2)3, the ligand is said to be polydentate. Ethylenediaminetetraacetate ion (EDTA4–) is an important hexadentate ligand. It can bind through two nitrogen and four oxygen atoms to a central metal ion.”
Definitions of Some Important Terms Pertaining to Coordination Compounds – “… NO2– ion can coordinate either through nitrogen or through oxygen to a central metal atom/ion. Similarly, SCN– ion can coordinate through the sulphur or nitrogen atom.”