Solveeit Logo
Login

Question

Question: Number of isomers of Co(NH3)5NO2NO32...

Number of isomers of Co(NH3)5NO2NO32

Answer

3

Explanation

Solution

The given coordination compound is Co(NH3)5NO2NO32. This formula is likely a typo and should be interpreted as [Co(NH3)5NO2](NO3)2.

Let's analyze the complex:

  • The central metal ion is Cobalt (Co).
  • The ligands are Ammine (NH3) and Nitrito/Nitro (NO2-).
  • The counter ions are Nitrate (NO3-).

To determine the oxidation state of Co:

Let the oxidation state of Co be x.

  • NH3 is a neutral ligand (charge = 0).
  • NO2- is a uninegative ligand (charge = -1).
  • NO3- is a uninegative counter ion (charge = -1).

The complex ion is [Co(NH3)5NO2]. The overall charge of the compound is 0. Since there are two NO3- counter ions, their total charge is -2. Therefore, the complex ion [Co(NH3)5NO2] must have a charge of +2. So, x + 5(0) + (-1) = +2 x - 1 = +2 x = +3 Thus, Cobalt is in the +3 oxidation state, i.e., Co(III).

The coordination number of Co is 5 (from NH3) + 1 (from NO2-) = 6. This indicates an octahedral geometry. The complex ion is of the type MA5B.

Now, let's identify the possible types of isomerism:

  1. Geometrical Isomerism: For an octahedral complex of the type MA5B, there is only one possible arrangement of ligands. Thus, no geometrical isomers are possible.

  2. Optical Isomerism: Since MA5B complexes possess planes of symmetry (e.g., a plane containing the central metal and the five A ligands, and bisecting the B ligand), they are achiral and do not exhibit optical isomerism.

  3. Linkage Isomerism: This type of isomerism arises when a ligand can coordinate to the central metal through more than one different donor atom. The NO2- ligand is an ambidentate ligand, meaning it can coordinate through:

    • The nitrogen atom: forming a nitro complex (-NO2, Co-N bond).
    • An oxygen atom: forming a nitrito complex (-ONO, Co-O bond).

    This leads to two linkage isomers:

    • Isomer 1 (Nitro form): [Co(NH3)5(NO2)](NO3)2 (Pentaammine-nitro-cobalt(III) nitrate)
    • Isomer 2 (Nitrito form): [Co(NH3)5(ONO)](NO3)2 (Pentaammine-nitrito-cobalt(III) nitrate)

  4. Ionization Isomerism: This occurs when an anion inside the coordination sphere exchanges places with an anion outside the coordination sphere (counter ion). In our complex [Co(NH3)5NO2](NO3)2, the ligand inside is NO2- and the counter ion is NO3-.

    If one NO3- enters the coordination sphere and NO2- leaves, we get an ionization isomer:

    • Isomer 3 (Nitrato form): [Co(NH3)5(NO3)](NO2)(NO3) (Pentaammine-nitrato-cobalt(III) nitrite nitrate)

      • Let's verify the charge: [Co(III) + 5(NH3) + (NO3-)] = [+3 + 5(0) + (-1)] = +2. The counter ions are NO2- and NO3-, which sum to -2. So, the formula is consistent.

Other types of isomerism (hydrate, coordination, ligand, solvate) are not applicable to this complex.

Summary of distinct isomers:

  1. [Co(NH3)5(NO2)](NO3)2 (Nitro form, original complex)
  2. [Co(NH3)5(ONO)](NO3)2 (Nitrito form, linkage isomer of 1)
  3. [Co(NH3)5(NO3)](NO2)(NO3) (Nitrato form, ionization isomer of 1 and 2)

These three compounds are chemically distinct isomers.

Explanation of the solution:

The complex [Co(NH3)5NO2](NO3)2 exhibits two types of isomerism:

  1. Linkage Isomerism: The ambidentate NO2- ligand can bond through nitrogen (nitro form) or oxygen (nitrito form), giving [Co(NH3)5(NO2)](NO3)2 and [Co(NH3)5(ONO)](NO3)2.
  2. Ionization Isomerism: The NO2- ligand inside the coordination sphere can exchange with the NO3- counter ion, leading to [Co(NH3)5(NO3)](NO2)(NO3).

No geometrical or optical isomers are possible for this MA5B type complex.

Therefore, a total of 3 distinct isomers exist.