The octahedral diamagnetic low spin complex among the following is

CONCEPT:

Diamagnetism and Low Spin Complexes

• Diamagnetic complexes have all paired electrons, resulting in no net magnetic moment.
• In octahedral complexes, the electronic configuration can be influenced by the nature of ligands, leading to high spin or low spin configurations.
• Strong field ligands such as CN^- and NH₃ cause pairing of electrons, resulting in low spin complexes.

EXPLANATION:

• [NiCl₄]^2-:
  • Nickel (Ni²⁺) has a d⁸ configuration.
  • Chloride (Cl^-) is a weak field ligand, leading to a high spin complex.
  • High spin d⁸ configuration in a tetrahedral field does not result in a diamagnetic complex.
• [CoCl₆]^3-:
  • Cobalt (Co³⁺) has a d⁶ configuration.
  • Chloride (Cl^-) is a weak field ligand, leading to a high spin complex.
  • High spin d⁶ configuration in an octahedral field does not result in a diamagnetic complex.
• [CoF₆]^3-:
  • Cobalt (Co³⁺) has a d⁶ configuration.
  • Fluoride (F^-) is a weak field ligand, leading to a high spin complex.
  • High spin d⁶ configuration in an octahedral field does not result in a diamagnetic complex.
• [Co(NH₃)₆]³⁺:
  • 
    
  • Cobalt (Co³⁺) has a d⁶ configuration.
  • Ammonia (NH₃) is a strong field ligand, leading to a low spin complex.
  • Low spin d⁶ configuration in an octahedral field results in all paired electrons, making it diamagnetic.

Therefore, the octahedral diamagnetic low spin complex among the given options is [Co(NH₃)₆]³⁺.