Question

The pair(s) of complexes wherein both exhibit tetrahedral geometry is(are)
(Note: $py =$ pyridine
Given: Atomic numbers of $Fe , Co , Ni$ and $Cu$ are $26,27,28$ and $29$ , respectively)

• A. $\left[ FeCl _{4}\right]^{-}$and $\left[ Fe ( CO )_{4}\right]^{2-}$
• B. $\left[ Co ( CO )_{4}\right]^{-}$and $\left[ CoCl _{4}\right]^{2-}$
• C. $\left[ Ni ( CO )_{4}\right]$ and $\left[ Ni ( CN )_{4}\right]^{2-}$
• D. $\left[ Cu ( py )_{4}\right]^{+}$and $\left[ Cu ( CN )_{4}\right]^{3-}$

Answer 1

Answer: (A), (B), (D)

(A) $\left[ FeCl _{4}\right]^{-}$
$Fe ^{+3}=3 d ^{5}, Cl ^{-}$ weak field liganol $sp ^{3}$
$\left[ Fe ( CO )_{4}\right]^{-2}$
$Fe ^{-2} =3 d ^{8} 4 s ^{2}$
$CO$ strong field liganol pairing occurs
$Fe ^{-2}=3 d ^{10}$
hence $sp ^{3}$
(B) $\left[ Co ( CO )_{4}\right]^{-}$
$Co =3 d ^{8} 4 s ^{2} $
due to $CO$ pairing occurs
Hence $=3 d ^{10}$
$\left[ CoCl _{4}\right]^{-2}$
$Co ^{+2}=3 d ^{7}$,
$Cl ^{-}$ weak field liganol $sp ^{3}$
(D) $\left[ Cu ( Py )_{4}\right]^{+1}$
$Cu ^{+1}=3 d ^{10}, sp ^{3}$
$\left[ Cu ( CN )_{4}\right]^{-3}$
$Cu ^{+1}=3 d ^{10}, sp ^{3}$