Question

For octahedral Mn(II) and tetrahedral Ni(II) complexes, consider the following statements:

(I) both the complexes can be high spin.
(II) Ni(II) complex can very rarely be low spin.
(III) with strong field ligands, Mn(II) complexes can be low spin.
(IV) aqueous solution of Mn(II) ions is yellow in colour.

The correct statements are :

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

Hint:

Recall that \(\mathrm{Mn^{2+}}\) (d5) can be high or low spin in an octahedral field, tetrahedral \(\mathrm{Ni^{2+}}\) (d8) is nearly always high spin, and aqueous \(\mathrm{Mn^{2+}}\) is pale pink.

Answer 1

The Correct Option is D

(I) True: octahedral Mn(II) (d5) is high spin with weak field ligands; tetrahedral Ni(II) (d8) complexes are high spin because \(\Delta_t\) is small.
(II) True: low spin tetrahedral Ni(II) complexes are very rare.
(III) True: with strong field ligands (e.g. \(\mathrm{CN^-}\)) octahedral Mn(II) forms low spin (\(t_{2g}^5\), one unpaired electron) complexes.
(IV) False: aqueous \(\mathrm{Mn^{2+}}\) is pale pink (nearly colourless), not yellow, since its d-d transitions are spin forbidden.
Correct statements: (I), (II) and (III) only.
Answer: (4) (I), (II) and (III) only