Question

Which of the following statements are true about [CoF₆]^3- ion?
I. The complex has octahedral geometry.
II. Coordination number of Co is 3 and oxidation state is + 6.
III. The complex is sp³d² hybridised.
IV. It is a high spin complex.

• A. I,II and IV
• B. I,III and IV
• C. II and IV
• D. II,III and IV

Answer 1

The Correct Option is B

• I. The complex has octahedral geometry: This statement is false for [CoF₆]³⁻. The geometry of this complex is octahedral only if it has a coordination number of 6, but the correct coordination number in this case is 3 (as per statement II).
• II. Coordination number of Co is 3 and oxidation state is +6: This statement is false. The oxidation state of Co in [CoF₆]³⁻ is +3, and the coordination number is 6, not 3.
• III. The complex is sp³d² hybridised: This statement is true. Since the complex has a coordination number of 6, the cobalt ion uses sp³d² hybridisation for octahedral geometry.
• IV. It is a high spin complex: This statement is true for [CoF₆]³⁻. Since it is a 3d⁶ configuration and in the absence of strong field ligands like F⁻, it forms a high spin complex.

Therefore, the correct answer is (B) I, III, and IV.

Answer 2

I. The complex has octahedral geometry:
The\( [CoF_6]^{3−}[CoF_6]^{3-}[CoF6​]^{3−}\) complex has a coordination number of 6 because it is coordinated to 6 fluoride ions. Thus, the complex will have octahedral geometry.
This statement is true.

II. Coordination number of Co is 3 and oxidation state is +6:
The coordination number of \( [CoF_6]^{3−}[CoF_6]^{3-}[CoF6​]^{3−}\) is 6, as it is bonded to 6 fluoride ions. The oxidation state of cobalt is calculated as follows:
The charge of the fluoride ion is -1, and there are 6 fluoride ions, so the total charge contributed by fluoride is -6. The overall charge on the complex is -3, so the charge on Co must be +3.
Therefore, the oxidation state of Co is +3, not +6.
This statement is false.

III. The complex is sp³d² hybridised:
The coordination number of 6 indicates that the central metal ion is involved in six bonds, which leads to sp³d² hybridisation in an octahedral arrangement.
This statement is true.

IV. It is a high-spin complex:
Cobalt in the +3 oxidation state has an electron configuration that typically results in a low-spin complex when paired with ligands like fluoride. However, fluoride is a weak field ligand, which does not favor spin pairing, and the complex will not be high-spin.
This statement is false.

Thus, the correct answer is (B) I, III and IV.