Sample 1Medium
Two structures of the octahedral ion [CoCl2(en)2]⁺ are drawn. In X the two Cl atoms are on adjacent corners, 90° apart; in Y they are on opposite corners, 180° apart. Each ethane-1,2-diamine (en) spans two adjacent corners. Which statement is correct?
- A
Y is optically active; X is optically inactive
- B
Both X and Y are optically active
- C
X and Y are linkage isomers
- D
X is optically active and exists as a pair of enantiomers; Y is optically inactive
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The answer is D.X is the cis isomer and Y the trans isomer of [CoCl2(en)2]⁺. The cis form has no plane of symmetry and exists as two non-superimposable mirror images, while the trans form is optically inactive.
- A.
The trans form Y has a mirror plane through the Co and both Cl atoms, so it is optically inactive.
- B.
Only the cis form lacks a mirror plane; the trans form is superimposable on its mirror image.
- C.
Linkage isomers differ in which atom of an ambidentate ligand binds; X and Y are geometrical (cis–trans) isomers.
NCERT: Class 12 Chemistry, Chapter 5
Sample 2NEET level
Match the pairs of compounds in List I with the type of isomerism they show in List II. List I: A. [Co(NH3)5(NO2)]Cl2 and [Co(NH3)5(ONO)]Cl2 B. [Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6] C. [Co(NH3)5(SO4)]Br and [Co(NH3)5Br]SO4 D. [Cr(H2O)6]Cl3 and [Cr(H2O)5Cl]Cl2·H2O List II: I. Ionisation isomerism II. Solvate isomerism III. Linkage isomerism IV. Coordination isomerism
- A
A-IV, B-III, C-I, D-II
- B
A-III, B-IV, C-II, D-I
- C
A-III, B-IV, C-I, D-II
- D
A-I, B-IV, C-III, D-II
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The answer is C.NO2⁻ binding through N or O gives linkage isomers, and interchange of ligands between cationic and anionic complexes gives coordination isomers. Exchange of a ligand with a counter ion (SO4²⁻/Br⁻) gives ionisation isomers, and water as ligand or as free solvent gives solvate (hydrate) isomers.
- A.
Swaps linkage and coordination isomerism.
- B.
Swaps ionisation and solvate isomerism.
- D.
Swaps linkage and ionisation isomerism.
NCERT: Class 12 Chemistry, Unit 5 (Coordination Compounds), Isomerism in Coordination Compounds: Structural Isomerism