Question 1

What is ionisation isomerism in coordination compounds?

Accepted Answer

Ionisation isomerism occurs when a ligand and a counter-ion exchange places. For example, [Co(NH₃)₅Br]SO₄ contains a [Co(NH₃)₅Br]²⁺ complex ion with SO₄²⁻ outside, while [Co(NH₃)₅SO₄]Br contains a [Co(NH₃)₅SO₄]⁺ complex ion with Br⁻ outside.

Question 2

What is the difference between nitro and nitrito linkage isomers?

Accepted Answer

They contain the same ambidentate NO₂⁻ ligand, but it coordinates through a different atom. In the nitro form, NO₂⁻ bonds to cobalt through nitrogen; in the nitrito form, ONO⁻ bonds through oxygen.

Question 3

How do hydrate isomers differ?

Accepted Answer

Hydrate isomers have the same overall composition but distribute water differently between the coordination sphere and the crystal lattice. The forms of CrCl₃·6H₂O are [Cr(H₂O)₆]Cl₃, [Cr(H₂O)₅Cl]Cl₂·H₂O and [Cr(H₂O)₄Cl₂]Cl·2H₂O, containing six, five and four coordinated water molecules respectively.

Question 4

What is coordination isomerism?

Accepted Answer

Coordination isomerism occurs in compounds containing both cationic and anionic complex ions. The metal centres exchange coordination spheres, producing [Co(NH₃)₆][Cr(CN)₆] and [Cr(NH₃)₆][Co(CN)₆].

Question 5

What are fac and mer isomers?

Accepted Answer

Fac and mer describe the two geometrical arrangements of an octahedral MA₃B₃ complex. In fac, the three identical ligands occupy one face and are mutually cis; in mer, they lie in a plane through the metal and include a trans pair.

Same Formula, Different Complex: Four Faces of Isomerism

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