Question:

The octahedral diamagnetic low spin complex among the following is

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In octahedral complexes, the ligand field strength determines whether the com plex will be high spin or low spin.

Updated On: Mar 21, 2025
  • [CO(NH3)6]3+
  • [COF6]3-
  • [COCl6]3- 
  • [Fe(H2O)6]3+
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The Correct Option is A

Solution and Explanation

Step 1: Understanding Coordination Complexes 

The coordination number (CN) for [Co(NH3)6]3+ is 6, indicating an octahedral geometry. Ammonia (NH3) is a strong field ligand (SFL) as per the spectrochemical series.

Step 2: Electron Configuration of Co3+

  • Atomic configuration of Co: \([Ar] 3d^7 4s^2\)
  • Configuration of Co3+ (after losing 3 electrons): \([Ar] 3d^6\)

Step 3: Effect of Strong Field Ligand

Due to the strong field nature of NH3, it causes pairing of electrons in the 3d orbitals. The electronic configuration of Co3+ in the presence of NH3 becomes:

\[ t_{2g}^6 \, e_g^0 \]

This configuration indicates:

  • All electrons are paired, making the complex diamagnetic.
  • It is a low-spin octahedral complex.

Conclusion:

[Co(NH3)6]3+ is a diamagnetic, low-spin octahedral complex.

Final Answer: [Co(NH3)6]3+ is the correct option.

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Concepts Used:

Coordination Compounds

A coordination compound holds a central metal atom or ion surrounded by various oppositely charged ions or neutral molecules. These molecules or ions are re-bonded to the metal atom or ion by a coordinate bond.

Coordination entity:

A coordination entity composes of a central metal atom or ion bonded to a fixed number of ions or molecules.

Ligands:

A molecule, ion, or group which is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is commonly called a ligand. It may be either neutral, positively, or negatively charged.