Question

Which of the following complexes exhibit(s) magnetic moment close to 2 Bohr Magneton?
[\(\text{Fe}(\text{H}_2\text{O})_6\)](\(\text{NO}_3\))\(_2\), \(\text{K}_2\)[\(\text{MnCl}_4\)], \(\text{K}_4\)[\(\text{Mn}(\text{CN})_6\)], and [\(\text{Ni}(\text{CO})_4\)]

• A. Only \(\text{K}_4\)[\(\text{Mn}(\text{CN})_6\)]
• B. \(\text{K}_2\)[\(\text{MnCl}_4\)] and \(\text{K}_4\)[\(\text{Mn}(\text{CN})_6\)]
• C. [\(\text{Fe}(\text{H}_2\text{O})_6\)](\(\text{NO}_3\))\(_2\) and \(\text{K}_2\)[\(\text{MnCl}_4\)]
• D. \(\text{K}_4\)[\(\text{Mn}(\text{CN})_6\)] and [\(\text{Ni}(\text{CO})_4\)]

Hint:

If the magnetic moment is close to a whole number, that whole number minus one or the digit before the decimal point usually represents the number of unpaired electrons.
For example, a magnetic moment of 1.73 BM (\(\approx 2\) BM) indicates 1 unpaired electron.
A magnetic moment of 5.92 BM indicates 5 unpaired electrons.

Answer 1

The Correct Option is A

To determine which of the given complexes exhibit a magnetic moment close to 2 Bohr Magneton, we need to analyze the electron configuration and oxidation states of the central metal ions in each complex.

1. [\(\text{Fe}(\text{H}_2\text{O})_6\)](\(\text{NO}_3\))\(_2\):
   • Oxidation state of Fe: +2 as \(\text{Fe}^{2+}\).
   • Electronic configuration of \(\text{Fe}^{2+}\): \([Ar] 3d^6\).
   • The complex is typically high-spin because \(\text{H}_2\text{O}\) is a weak field ligand, resulting in 4 unpaired electrons.
   • Magnetic moment (\(\mu\)) is calculated using the formula: \(\mu = \sqrt{n(n+2)}\) BM, where \(n\) is the number of unpaired electrons.
   • For 4 unpaired electrons, \(\mu = \sqrt{4(4+2)} = \sqrt{24} \approx 4.9\) BM, much larger than 2 BM.
2. \(\text{K}_2\)[\(\text{MnCl}_4\)]:
   • Oxidation state of Mn: +2 as \(\text{Mn}^{2+}\).
   • Electronic configuration of \(\text{Mn}^{2+}\): \([Ar] 3d^5\).
   • Being a high spin complex with chloride ligands, it typically possesses 5 unpaired electrons.
   • For 5 unpaired electrons, \(\mu = \sqrt{5(5+2)} = \sqrt{35} \approx 5.9\) BM, which is also much larger than 2 BM.
3. \(\text{K}_4\)[\(\text{Mn}(\text{CN})_6\)]:
   • Oxidation state of Mn: +2 as \(\text{Mn}^{+4}\).
   • Electronic configuration of \(\text{Mn}^{4+}\): \([Ar] 3d^3\).
   • As \(\text{CN}^-\) is a strong field ligand, it leads to pairing up of electrons resulting in a low spin complex.
   • This provides 1 unpaired electron in this configuration.
   • For 1 unpaired electron, \(\mu = \sqrt{1(1+2)} = \sqrt{3} \approx 1.73\) BM, close to 2 BM.
4. [\(\text{Ni}(\text{CO})_4\)]:
   • Oxidation state of Ni: 0 as \(\text{Ni}^{0}\).
   • Electronic configuration of \(\text{Ni}^{0}\): \([Ar] 3d^{10}\ 4s^{0}\). All electrons are paired in the d-subshell.
   • Magnetic moment for 0 unpaired electrons is 0 BM, indicating it’s diamagnetic.

Based on the above analysis, only \(\text{K}_4\)[\(\text{Mn}(\text{CN})_6\)] has a magnetic moment close to 2 Bohr Magneton.