Question

Among the following species, identify the isostructural pairs
$N{F}_3,N{O}_3^{-},B{F}_3,H_3{O}^{+},H{N}_3$

• A. $[N{F}_3,N{O}_3^{-}]$ and $[B{F}_3,H_3^{+}O]$
• B. $[N{F}_3,H{N}_3],[N{O}_3^{-},B{F}_3]$
• C. $[N{F}_3,H_3{O}^{+}]$ and $[N{O}_3^{-},B{F}_3]$
• D. $[N{F}_3,H_3^{+}O]$ and $[H{N}_3,B{F}_3]$

Answer 1

Answer: (C)

For species to be isostructural they should have same hybridized state same number of $b.p.$ and $l.p.$

Hybridized state	L. p.
$N{F}_{3}H=\frac{1}{2}(5+3)=4$ $\Rightarrow N$ is $s{p}^3$ hybridised	1
$N{O}_3^{-}H=\frac{1}{2}(5+1)=3$ $\Rightarrow N$ is $s{p}^2$ hybridised	1
$B{F}_{3}H=\frac{1}{2}(3+3)=3$ $\Rightarrow B$ is $s{p}^2$ hybridised	0
$B_3{O}^{+}H=\frac{1}{2}(6+3-1)=4$ $\Rightarrow O$ is $s{p}^3$ hybridised	0

These three $s{p}^2$-hybrid orbitals are attached to each other trigonally with an angle of $120^{\circ }$ and they are overlapped with three $p$-orbitals of three $F$-atoms on their axes. Hence the geometry of $B{F}_3$ molecule is trigonal planar.

Thus isostructural pairsare $[N{F}_3,H_3{O}^{+}]$ and $[N{O}_3^{-},B{F}_3]$