Question

what are trhe conditions for the two species to be isostructural?

Answer 1

They should have same hybridisation with same number of lone pair to have the same structure. For ex.,
Find the hybridisation and lone pair using the following formula.

$$\begin{gathered} H=\frac{1}{2}[Valence{e}^{-}ofthecentralatom+Noofmaonvalentatom-cation+anion] \\ Lonepair=H-Noofsuuroundingatom. \end{gathered}$$

If there is mismatching in the values for any one of the molecules given you can say they are not isostructural.

1. CO₃^2- and NO₃^{-
$$\begin{gathered} C{O_3}^{2-}:H=\frac{1}{2}[4+0-0+2] \\ =\frac{6}{2} \\ =3\left(s{p}^2\right) \\ Lonepair=3-3=0 \\ N{O_3}^{-}:H=\frac{1}{2}[5+0-0+1] \\ =\frac{6}{2} \\ =3\left(s{p}^2\right) \\ Lonepair=3-3=0 \\ Thusbothareisostructural:Trigonal\left(s{p}^2\right) \\ 2.PC{l_4}^{+}:H=\frac{1}{2}[5+4-1+0] \\ =\frac{8}{2} \\ =4\left(s{p}^3\right) \\ Lonepair=4-4=0 \\ SiC{l}_4:H=\frac{1}{2}[4+4-0+0] \\ =\frac{8}{2} \\ =4\left(s{p}^3\right) \\ Lonepair=4-4=0 \\ Thusbothareisostructural:Tetrahedral\left(s{p}^3\right) \\ 3.P{F}_5:H=\frac{1}{2}[5+5-0+0] \\ =\frac{10}{2} \\ =5\left(s{p}^{3}d\right) \\ Lonepair=5-5=0 \\ Ithastrigonalbipyramidalstr. \\ Br{F}_5:H=\frac{1}{2}[7+5-0+0] \\ =\frac{12}{2} \\ =6\left(s{p}^3{d}^2\right) \\ Lonepair=6-5=1 \\ Ithasdistortedoctahedralstructure \\ 4.Al{F_6}^{3-}:H=\frac{1}{2}[3+6-0+3] \\ =\frac{12}{2} \\ =6\left(s{p}^3{d}^2\right) \\ Lonepair=6-6=0 \\ S{F}_6:H=\frac{1}{2}[6+6-0+0] \\ =\frac{12}{2} \\ =6\left(s{p}^3{d}^2\right) \\ Lonepair=6-6=0 \\ Thusbothareisostructural:Octahedral \end{gathered}$$}