Question

Statement 1: $N{Me}_3$ and $N{\left(Si{Me}_3\right)}_3$ are not isostructural.
Statement 2: $N{Me}_3$ and $N{\left(Si{Me}_3\right)}_3$ have the same steric number.

Regarding the above statements which of the following is/are correct?

• A. Both the statements are true
• B. Both the statements are false
• C. Only statement 1 is true
• D. Only statement 2 is true

Answer 1

The correct option is C Only statement 1 is true

$N{\left(Si{Me}_3\right)}_3$ is trigonal planar in shape because of $p\pi -d\pi$ back bonding between the vacant d- orbital of $Si$ and the filled $2p$ orbital (or lone pair) of $N$ atom. All the bond lenghts are equal having a partial double bond character and the structure is shown below.
So, the steric number of$N{\left(Si{Me}_3\right)}_3$ is 3.

In $N{Me}_3$, there is no such $p\pi -d\pi$ back bonding as carbon does not have vacant $d$-orbitals.
The steric number of $N{Me}_3$ is 4 and its structure is pyramidal with lone pair at its apex.