An ambidentate ligand is a ligand that has two different donor atoms, but it uses only ONE of them at a time to bond the metal. For example, the nitrite ion NO2- can bond through nitrogen (nitrito-N) or through oxygen (nitrito-O). Memory hook: "ambi = both ends, but pick one door."
The nitrite ion NO2- is ambidentate: it can bond the metal (M) through its nitrogen atom (nitrito-N) or through an oxygen atom (nitrito-O). Only one atom bonds at a time, giving two linkage isomers.
Your doubts, answered
What exactly is an ambidentate ligand?
It is a monodentate ligand (donates through one atom at a time) that has TWO different atoms that could donate. It can attach to the metal through either atom, but never both at once. So it still counts as monodentate. The word 'ambi' means 'both' and 'dentate' means 'tooth' - it has two possible teeth but bites with only one.
What is the difference between ambidentate and bidentate?
A bidentate ligand (like ethane-1,2-diamine 'en') uses TWO donor atoms at the SAME time to grip the metal, forming a ring. An ambidentate ligand has two possible donor atoms but uses only ONE at a time. So bidentate = grips with both hands together; ambidentate = has two hands but uses one. This is a very common NEET trap.
Why is SCN- (thiocyanate) called ambidentate?
The thiocyanate ion has both a sulphur (S) atom and a nitrogen (N) atom that can donate. If it bonds through S it is called thiocyanato-S (or just thiocyanato). If it bonds through N it is called thiocyanato-N (isothiocyanato). Because it can choose either S or N, it is ambidentate.
What is the difference between nitrito-N and nitrito-O?
NO2- can bond in two ways. When the nitrogen atom donates, it is called nitrito-N (older name: nitro), written as -NO2. When an oxygen atom donates, it is called nitrito-O (older name: nitrito), written as -ONO. Same ion, two names, based on which atom touches the metal.
Is CN- an ambidentate ligand?
Yes. The cyanide ion CN- can bond through carbon (cyanido-C, older name cyanido) or through nitrogen (cyanido-N, isocyanido). It usually bonds through carbon, but because both atoms can donate, CN- is ambidentate. NCERT lists CN- along with NO2- and SCN- as the main ambidentate examples.
How does an ambidentate ligand cause linkage isomerism?
Because the same ligand can bond through two different atoms, you get two different compounds with the same formula. For example [Co(NH3)5(NO2)]Cl2 can be nitrito-N (metal-N) or nitrito-O (metal-O). These two forms are called linkage isomers. So ambidentate ligands are the CAUSE of linkage isomerism - NEET asks this a lot.
⚠️ The NEET trap ✗ SCN- and NO2- are bidentate ligands because they have two donor atoms. ✓ Having two possible donor atoms does NOT make a ligand bidentate. Bidentate means both atoms donate at the SAME time to form a ring. SCN-, NO2- and CN- use only one atom at a time, so they are monodentate but AMBIdentate. 🧠 Two donor atoms available is not the same as two donor atoms used together. Ambidentate = two doors, walk through one.
Real NEET questions
2026
Which one of the following is an ambidentate ligand?
A · Ethane-1,2-diamine
B · Ethylenediaminetetraacetate ion
C · Thiocyanate ✓
D · Oxalate
Solution: Ambidentate means two different donor atoms, only one used at a time. Ethane-1,2-diamine (en) is bidentate (two N donors together). EDTA is hexadentate (4 O + 2 N). Oxalate is bidentate (two O donors together). Thiocyanate (SCN-) can bond through S or through N, so it is the ambidentate ligand. Answer: C.
2024
Match List-I (Complex) with List-II (Type of isomerism): (a) [Co(NH3)5(NO2)]Cl2 (b) [Co(NH3)5(SO4)]Br (c) [Co(NH3)6][Cr(CN)6] (d) [Co(H2O)6]Cl3. List-II: (i) Solvate isomerism (ii) Linkage isomerism (iii) Ionization isomerism (iv) Coordination isomerism.
A · (a)-(i), (b)-(iii), (c)-(iv), (d)-(ii)
B · (a)-(i), (b)-(iv), (c)-(iii), (d)-(ii)
C · (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
D · (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i) ✓
Solution: NO2- is an ambidentate ligand, so [Co(NH3)5(NO2)]Cl2 shows LINKAGE isomerism (nitrito-N vs nitrito-O) -> (a)-(ii). [Co(NH3)5(SO4)]Br can swap SO4 and Br between inside and outside the sphere -> ionization -> (b)-(iii). [Co(NH3)6][Cr(CN)6] has metals that can swap ligands -> coordination -> (c)-(iv). [Co(H2O)6]Cl3 has water that can move in/out of the lattice -> solvate -> (d)-(i). Answer: D.
2026
Match List-I with List-II: (a) [Pt(NH3)2Cl2] (b) [Co(en)3]^3+ (c) [Co(NH3)5(NO2)]Cl2 (d) [Cr(H2O)6]Cl3. List-II: (i) Optical (ii) Solvate (iii) Geometrical (iv) Linkage.
A · (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
B · (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
C · (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
D · (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii) ✓
Solution: [Pt(NH3)2Cl2] is square planar -> cis/trans -> geometrical (iii). [Co(en)3]^3+ has three bidentate 'en' rings -> chiral -> optical (i). [Co(NH3)5(NO2)]Cl2 contains the ambidentate NO2- -> linkage (iv). [Cr(H2O)6]Cl3 has water that can shift into the lattice -> solvate (ii). So (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii). Answer: D.
Solved Coordination Compounds NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What are the three main ambidentate ligands in NCERT?
NCERT lists NO2- (nitrite: bonds through N or O), SCN- (thiocyanate: bonds through S or N), and CN- (cyanide: bonds through C or N). Remembering these three is enough for NEET.
Are ambidentate ligands monodentate or bidentate?
They are monodentate. They donate through only one atom at a time. They just have a second possible donor atom to choose from, which makes them ambidentate as well.
How do we write the name for each bonding mode?
For NO2-: nitrito-N (through N) and nitrito-O (through O). For SCN-: thiocyanato-S and thiocyanato-N (isothiocyanato). For CN-: cyanido-C and cyanido-N (isocyanido). The italic letter shows the donor atom.
Why do ambidentate ligands matter for NEET?
They are the reason behind linkage isomerism, which appears in NEET match-the-column questions almost every year (2024, 2026). If a complex contains NO2-, SCN- or CN- as a single-atom donor, expect linkage isomerism as the answer.
