Question

The configurations of the complexes of manganese A, B respectively are t$_{2g}^3$ e$_g^1$, t$_{2g}^4$ e$_g^0$. Then A, B are:

• A. [Mn(H$_2$O)$_6$]$^{2+}$, [Mn(CN)$_6$]$^{3-}$
• B. [Mn(H$_2$O)$_6$]$^{3+}$, [Mn(CN)$_6$]$^{4-}$
• C. [Mn(H$_2$O)$_6$]$^{3+}$, [Mn(CN)$_6$]$^{4-}$
• D. [Mn(H$_2$O)$_6$]$^{3+}$, [Mn(CN)$_6$]$^{3-}$

Hint:

Remember the spectrochemical series: weak field ligands (like H$_2$O) lead to high spin complexes, and strong field ligands (like CN$^-$) lead to low spin complexes, especially for d$^4$ to d$^7$ configurations in octahedral fields.

Answer 1

The Correct Option is D

Step 1: Determine the oxidation state of Mn in each complex and the nature of the ligands.
Manganese (Mn) has an electronic configuration of [Ar] 3d$^5$ 4s$^2$. Complex A: [Mn(H$_2$O)$_6$]$^{n+$}
Water (H$_2$O) is a weak field ligand, leading to a high spin complex. The configuration is given as t$_{2g}^3$ e$_g^1$. This means there are 4 unpaired electrons.
If Mn is in the +2 oxidation state (Mn$^{2+}$), its configuration is 3d$^5$. In a weak field octahedral complex, the configuration would be t$_{2g}^3$ e$_g^2$ (5 unpaired electrons).
If Mn is in the +3 oxidation state (Mn$^{3+}$), its configuration is 3d$^4$. In a weak field octahedral complex, the configuration would be t$_{2g}^3$ e$_g^1$ (4 unpaired electrons), which matches the given configuration for A. Therefore, A is likely [Mn(H$_2$O)$_6$]$^{3+}$.
Complex B: [Mn(CN)$_6$]$^{m-$}
Cyanide (CN$^-$) is a strong field ligand, leading to a low spin complex. The configuration is given as t$_{2g}^4$ e$_g^0$. This means there are 2 unpaired electrons.
If Mn is in the +2 oxidation state (Mn$^{2+}$), its configuration is 3d$^5$. In a strong field octahedral complex, the configuration would be t$_{2g}^5$ e$_g^0$ (1 unpaired electron).
If Mn is in the +3 oxidation state (Mn$^{3+}$), its configuration is 3d$^4$. In a strong field octahedral complex, the configuration would be t$_{2g}^4$ e$_g^0$ (2 unpaired electrons), which matches the given configuration for B. Therefore, B is likely [Mn(CN)$_6$]$^{3-}$.
Step 2: Match the complexes with the given configurations.
Complex A ([Mn(H$_2$O)$_6$]$^{3+}$) corresponds to the t$_{2g}^3$ e$_g^1$ configuration (high spin d$^4$).
Complex B ([Mn(CN)$_6$]$^{3-}$) corresponds to the t$_{2g}^4$ e$_g^0$ configuration (low spin d$^4$).
Final Answer: \[ \boxed{[\text{Mn(H}_2\text{O)}_6]^{3+}, [\text{Mn(CN)}_6]^{3-}} \]