Question

Bond lengths of all the bonds between the central atom and the monovalent atom are equal in:

• A. $PC{l}_5$
• B. $P{F}_5$
• C. $B_2{H}_6$
• D. $I_{2}C{l}_6$

Answer 1

The correct option is B $P{F}_5$

• $B_2{H}_6$ and $I_{2}C{l}_6$ both are dimerized molecules of $B{H}_3$ and $IC{l}_3$ respectively.

• $B-H\left(bridged\right)bondlength=131pm$ & $B-H\left(terminal\right)bondlength=119pm$ in $B_2{H}_6$

• $I-Cl\left(bridged\right)bondlength=270pm$ & $I-Cl\left(terminal\right)bondlength=230pm$ in $I_{2}C{l}_6$

• $PC{l}_5$ has geometry trigonal bi-pyramidal and axial bonds are longer than equatorial bonds.

• $P{F}_5$ shows Berry pseudorotation.

This is a type of vibration causing molecules of certain geometries to isomerise by the exchange of two axial ligands for two of the equatorial ligands.

In $P{F}_5$ axial bonds & equatorial bonds inter-conversion occurs rapidly as shown below.
Thus, all the bonds are of equal bond length.