Coordination Compounds 2 Question 5
5. The incorrect statement is
(2019 Main, 10 April II)
(a) the gemstone, ruby, has $Cr^{3+}$ ions occupying the octahedral sites of beryl
(b) the color of $\left[CoCl\left(NH _3\right) _5\right]^{2+}$ is violet as it absorbs the yellow light
(c) the spin only magnetic moments of $\left.Fe\left(H _2 O\right) _6\right]^{2+}$ and $\left[Cr\left(H _2 O\right) _6\right]^{2+}$ are nearly similar
(d) the spin only magnetic moment of $\left[Ni\left(NH _3\right) _4\left(H _2 O\right) _2\right]^{2+}$ is $2.83$ $ BM$
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Answer:
Correct Answer: 5. (a)
Solution:
- The explanation of given statements are as follows :
(a) Ruby, a pink or blood-red coloured gemstone belongs to corundum $\left(Al _2 O _3\right.$, alumina) system which has trigonal crystalline lattice containing the repeating unit of $Al _2 O _3-Cr^{3+}$. So, ruby does not belong to beryl lattice $\left(Be _3 Al _2 Si _6 O _{18}\right)$.
Thus, statement (a) is incorrect.
(b) $\left[Co(Cl)\left(NH _3\right) _5\right]^{2+}$ is a low spin octahedral complex of $Co^{3+}$. It absorbs low energy yellow light and high energy complementary violet light will be shown off. Thus, statement (b) is correct.
(c) $\left[Fe\left(H _2 O\right) _6\right]^{2+}$ and $\left[Cr\left(H _2 O\right) _6\right]^{2+}$ are the high-spin octahedral complexes of $Fe^{2+}\left(3 d^{6}, n=4\right)$ and $Cr^{2+}\left(3 d^{5}, n=5\right)$ ions and weak field ligand, $H _2 O$ respectively. So, spin-only magnetic moment $=\sqrt{n(n+2)}$ of the complexes.
${\left[Fe\left(H _2 O\right) _6\right]^{2+}, } \mu _1 =\sqrt{4(4+2)} $
$\quad(n=4),\quad \quad =\sqrt{24}=4.89 BM $
${\left[Cr\left(H _2 O\right) _6\right]^{2+}, } \mu _2 =\sqrt{5(5+2)} $
$\quad(n=5),\quad \quad =\sqrt{35}=5.92 BM$
So, $\mu _1 \approx \mu _2$. Thus, statement (c) is correct.
(d) $\left[Ni\left(NH _3\right) _4\left(H _2 O\right) _2\right]^{2+}$ is also a high-spin octahedral complex of $Ni^{2+}\left(3 d^{8}, n=2\right)$
$ \mu=\sqrt{2(2+2)}=\sqrt{8}=2.83 $ $BM $
Thus, statement $(d)$ is correct.
BETA
