What NEET Asks
- Direct definition and examples of ambidentate and bridging ligands are frequently asked.
- Questions on linkage isomerism (due to ambidentate ligands) are common.
- Identifying bridging ligands in polynuclear complexes and their effect on coordination number/oxidation state.
Key Points
- Ambidentate Ligands: Ligands possessing two different donor atoms, but only one of which can form a coordinate bond at a time with the central metal atom. Examples: NO2- (nitro/nitrito), SCN- (thiocyanato/isothiocyanato), CN- (cyano/isocyano).
- Linkage Isomerism: Arises due to ambidentate ligands, where the same ligand can bind through different donor atoms, leading to isomers with different metal-ligand bonds (e.g., M-NO2 vs M-ONO).
- Bridging Ligands: Ligands that coordinate to two or more central metal atoms simultaneously, forming a bridge between them. This leads to the formation of polynuclear complexes.
- Examples of common bridging ligands: OH-, Cl-, O2-, CN-, CO (in specific complexes like Co2(CO)8).
- Unlike polydentate ligands, which bind to one metal through multiple sites, ambidentate ligands bind to one metal through one of two possible sites. Bridging ligands bind to multiple metals.
Must-Know Formula / Reaction
- Linkage Isomerism Example:
[Co(NH3)5(NO2)]Cl2(Pentaammine-nitrocobalt(III) chloride) - Co-NO2 bond[Co(NH3)5(ONO)]Cl2(Pentaammine-nitritocobalt(III) chloride) - Co-ONO bond- Here, NO2- is the ambidentate ligand, capable of coordinating through nitrogen (nitro) or oxygen (nitrito).
Common Mistakes
- Students often confuse ambidentate ligands with polydentate (chelating) ligands. Ambidentate ligands are always monodentate to a single metal center.
- Don't confuse the donor atoms in ambidentate ligands (e.g., N vs O for NO2-), which leads to incorrect IUPAC naming.
- Forgetting to identify bridging ligands in complex structures, which can affect the perception of coordination number around individual metal centers or the overall charge distribution.
Rapid Revision
Ambidentate ligands have two donor sites, one used at a time (e.g., NO2-, SCN-), causing linkage isomerism. Bridging ligands connect two or more metal centers (e.g., OH-, Cl-), forming polynuclear complexes. Always check donor atoms and coordination modes.