Question

Among the following, the correct statement is :

• A. $AlC{l}_3\text{can't form dimeric structure}$
• B. $\text{The Lewis acidity of}BC{l}_3\text{is lesser than that of}AlC{l}_3$
• C. $AlC{l}_3\text{has the three-centre two-elecron bonds in its dimeric structure}$
• D. $B{H}_3\text{has the three-centre two-electron bonds in its dimeric structure}$

Answer 1

The correct option is D $B{H}_3\text{has the three-centre two-electron bonds in its dimeric structure}$

(b) $BC{l}_3$ is stronger Lewis acid than $AlC{l}_3$ due to greater extent of $p_{\pi }-p_{\pi }$ back bonding in $AlC{l}_3$.
Thus, statement (b) is wrong
(a) $AlC{l}_3$ can form dimer through halogen bridging and exists as $A{l}_{2}C{l}_6$ because it has vacant d-orbitals which can accommodate electron from chlorine atom. Thus it does not form 3-centre 2- electrons bond.
Thus, statement (a) and (c) are wrong.

(d) The four terminal B-H bonds are​ regular two centre-two electron bonds. The two bridge (B-H-B) bonds are three​ centre-two electron bonds.​

Thus, statement (d) is correct.