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Identify the pair of coordination complexes in which both complexes exhibit the same type of structural isomerism and also have the same number of geometrical isomers.

1. [Co(NH3)4Cl2]Br and [Ni(en)2(NH3)2]Cl2
2. [Pt(NH3)4Cl2]Br2 and [Fe(gly)3]
3. [Pt(NH3)4Br2]Cl2 and Na2[CoBr2Cl2]
4. [Co(NO2)2(NH3)4]Cl and [Fe(NH3)4(CN)2]Br

Correct answer: [Co(NO2)2(NH3)4]Cl and [Fe(NH3)4(CN)2]Br

Solution

Structural isomerism in coordination complexes includes ionisation, linkage, coordination, solvate, etc. Both complexes in option D are octahedral with formula MA4B2X type: [Co(NO2)2(NH3)4]Cl (4+2 coordination) and [Fe(NH3)4(CN)2]Br. Each is of the MA4B2 type in the coordination sphere and hence shows exactly 2 geometrical isomers (cis and trans). Both show ionisation isomerism (the Cl/Br can exchange with the B-type ligand NO2/CN). Options A, B, C either differ in type of isomerism or number of geometrical isomers.

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