MCQ
Which among the following is a paramagnetic complex?

$($At. No. $Mo = 42, Pt = 78)$

  • A
    $[Co(NH_3)_6]^{3+}$
  • B
    $[Pt(en)Cl_2]$
  • $[CoBr_4]^{2-}$
  • D
    $Mo(CO)_6$

Answer

Correct option: C.
$[CoBr_4]^{2-}$
c
Magnetic Moments (spin only)- $\sqrt{n(n+2)}$

where $n=$ number of unpaired electron.

Number of unpaired $e^{-} s$ and corresponding magnetic moments

$1 \rightarrow 1.7$

$2 \rightarrow 2.8$

$3 \rightarrow 3.9$

$4 \rightarrow 4.9$

$5 \rightarrow 5.9$

since $B r^{-}$ is a weak feild ligand, so electrons in $C o^{2+}$ will not pair up.

the complex has $3$ unpaired electrons leaving it paramagnetic in nature.

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