Test: Isomerism in Coordination Compounds - I - NEET MCQ

Octahedral complexes of formula [Ma₄b₂] in which the two ligands b may be oriented cis or trans to each other, e.g.

Geometrical isomers (cis and trans) of [Co(NH₃)₄CI₂]⁺.

Ligand which can ligate through two different atoms is called ambidentate ligand. NO₂^- ion can coordinate either through nitrogen or through oxygen to a central metal atom/ion.

Hence, ligand show linkage isomerism, e.g. the complex [Co(NH₃)₅(NO₂)]CI₂ which is obtained as the red form, in which the nitrite ligand is bound through oxygen (—ONO) and as the yellow form, in which the nitrite ligand is bound through nitrogen (— NO₂). 

The complex [Co(NH₃)₄Br₂]CI show geometrical and ionisation isomerism.

Due to symmetry in the complex [Co(NH₃)₃CI₃], it failed to show optical isomerism. The type of coordination entity show fac and mer isomerism or geometrical isomerism.

The facial (fac) and meridional (mer) isomers of [Co(NH₃)₃CI₃]. 

Ionisation isomerism is due to the exchange of groups between the complex ion and the ions outside it, e.g. [Cr(H₂O)₄CI(NO₂)CI] and [Cr(H₂O)₄CI₂]NO₂ show ionisation isomerism. 

[CoNH₃CI₃] do not exhibit optical isomerism. Optical isomerism is shown by M(AA)₂X₂ type, M(AA)₃ type , [M(AA) B₂X₂] type complexes containing hexadentate ligand and ML_a L_b L_c L_d Left type.

Coordination isomerism is possible when both positive and negative ions of a salt are complex ions and two isomers differ in distribution of ligands in the cation and the anion.

All the three compounds, i.e. [PtCI₂(NH₃)₂], [PdCl₂Brl] and [Pt(NH₃)(py)(CI)(Br)] exhibit cis and trans isomerism.

cis platin is used as anticancer drug.

Linkage isomerism occurs when two or more atoms in a monodentate ligand may function as a donor, i.e. when an ambidentate ligand is present. e.g. , CN^- and SCN^-.

K[Ag(CN)₂]show linkage isomerism.
[CrCI(NH₃)₅] I₂ show ionisation isomerism.
[PtCI₄I₂] show geometrical isomerism.

This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex.

Due to symmetry in the complex [Cu(NH₃)₄]CI₂, it fails to show geometrical isomerism but all others show.

Geometrical isomerism is not observed in complexes of coordination number 4 having tetrahedral geometry. The platinumglycinato complex [ Pt(gly)2 show geometrical isomerism (cis and trans form).

For O.S:

X + 0 + 2(-1) = 1

X = 3

Coordination number is the number of molecules linked to the central atom.

Hence B is the correct answer.

Structure (a) = structure (c) and, structure (b) = structure (d)

[Co(NH₃)₄CI₂]⁺ exhibits geometrical isomerism.
cis-[Co(en)₂CI₂]⁺ because of the absence of symmetry elements exhibit optical isomerism.
[Co(NH₃)₅(NO₂)]CI₂ because of the presence of ambidentate (NO₂) ligand exhibit linkage isomerism. [Co(NH₃)₆][Cr(CN₎6] exhibits coordination isomerism because here, cation and anion both are complex.

(i) → (s), (ii) →(p), (iii) → (t), (iv) → (r)

(i) → (r,s), (ii) → (p,q,t), (iii) → (p,q,t), (iv) → (r,s)

For a complex of the type MABCD, three geometrical isomers are possible.

The complex has cis and trans isomers. The c/s has non-superimposable mirror images. Hence, total are 3.

[Cu(NH₃)₃CI][Pt(NH₃)CI₃], [Cu(NH₃)CI₃][Pt(NH₃)₃CI]
[Cu(NH₃)₄] [PtCI₄], [Pt(NH₃)₄] [CuCI₄]

This is [Ma₃b₃] type of complex and this has two geometrical isomers called facial (fac isomer) and meridional (mer isomer).

[Mabcd] type complexes exist in three isomeric forms. 

MX₆ and MX₅L type complexes do not exhibit geometrical isomerism, cis [Co(en)₂CI₂]⁺ because of the absence of symmetry elements exhibit optical isomerism.
[Co(NH₃)₅(NO₂)]CI₂ because of the presence of ambidentate (NO₂) ligand exhibit linkage isomerism. [CoNH₃)₆][Cr(CN)₆] exhibits coordination isomerism because here cation and anion both are complex.