Question

Number of paramagnetic complexes among the following is _______. \[ [\text{MnBr}_4]^{2-}, \, [\text{NiCl}_4]^{2-}, \, [\text{Ni(CN)}_4]^{2-}, \, [\text{Ni(CO)}_4], \, [\text{CoF}_6]^{3-}, \, [\text{Fe(CN)}_6]^{4-}, \, [\text{Mn(CN)}_6]^{3-}, \, [\text{Ti(CN)}_6]^{3-}, \, [\text{Cu(H}_2\text{O)}_6]^{2+}, \, [\text{Co(C}_2\text{O}_4)_3]^{3-} \]

Answer 1

Correct Answer: 7

\textcolor{red}{Step 1: Understand the concept of paramagnetism.}
A complex is paramagnetic if it has unpaired electrons. Paramagnetic complexes have unpaired d-electrons in their metal ion. \textcolor{red}{Step 2: Analyze each complex.}
- \([ \text{MnBr}_4 ]^{2-}\) contains \(\text{Mn}^{2+}\), which has 5 unpaired electrons, so it is paramagnetic.
- \([ \text{NiCl}_4 ]^{2-}\) contains \(\text{Ni}^{2+}\), which has 2 unpaired electrons, so it is paramagnetic.
- \([ \text{Ni(CN)}_4 ]^{2-}\) contains \(\text{Ni}^{2+}\), but cyanide is a strong field ligand that pairs electrons, making this complex diamagnetic.
- \([ \text{Ni(CO)}_4 ]\) contains \(\text{Ni}^{0}\), and carbon monoxide is a strong field ligand, so it pairs electrons, making it diamagnetic.
- \([ \text{CoF}_6 ]^{3-}\) contains \(\text{Co}^{3+}\), which has 6 unpaired electrons, so it is paramagnetic.
- \([ \text{Fe(CN)}_6 ]^{4-}\) contains \(\text{Fe}^{2+}\), and cyanide is a strong field ligand, so it pairs electrons, making it diamagnetic.
- \([ \text{Mn(CN)}_6 ]^{3-}\) contains \(\text{Mn}^{3+}\), which has 4 unpaired electrons, so it is paramagnetic.
- \([ \text{Ti(CN)}_6 ]^{3-}\) contains \(\text{Ti}^{3+}\), which has 1 unpaired electron, so it is paramagnetic. - \([ \text{Cu(H}_2\text{O)}_6 ]^{2+}\) contains \(\text{Cu}^{2+}\), which has 1 unpaired electron, so it is paramagnetic.
- \([ \text{Co(C}_2\text{O}_4)_3 ]^{3-}\) contains \(\text{Co}^{3+}\), which has 6 unpaired electrons, so it is paramagnetic.
\textcolor{red}{Step 3: Count the number of paramagnetic complexes.}
The paramagnetic complexes are: \[ [\text{MnBr}_4]^{2-}, \, [\text{NiCl}_4]^{2-}, \, [\text{CoF}_6]^{3-}, \, [\text{Mn(CN)}_6]^{3-}, \, [\text{Ti(CN)}_6]^{3-}, \, [\text{Cu(H}_2\text{O)}_6]^{2+}, \, [\text{Co(C}_2\text{O}_4)_3]^{3-} \] There are 7 paramagnetic complexes.