Question

$AC{l}_3$ is trigonal pyramidal and $EC{l}_3$ is trigonal planar. These two combine to give $AEC{l}_6$. Crystallographic studies and structural analysis reveal that $AEC{l}_6$ is an ionic compound. If the anion has a see-saw shape, then the shape of the cation is:

• A. Linear
• B. Bent
• C. Pentagonal bipyramidal
• D. Trigonal planar

Answer 1

The correct option is A

Linear

The anion has a see-saw shape – much like $S{F}_4$:

As you can see, there needs to be a lone pair and 4 ligands. This can happen if a chloride is abstracted from $EC{l}_3$ and given to $AC{l}_3$. That would make $EC{l}_3$ into $EC{l}_2^{+}$ - a linear molecule given there is an evident absence of a lone pair in the central atom E.