Given below are the statements about diborane.
(A) Diborane is prepared by the oxidation of NaBH4 an

Q: Why is diborane an electron-deficient molecule?

Because it does not have enough valence electrons to form standard 2-centre-2-electron bonds between all its atoms. It uses 3-centre-2-electron bonds to compensate.

Q: What is a 3-centre-2-electron bond?

It is a type of chemical bond where three atoms share two electrons. In diborane, the B-H-B bridge is a classic example, often called a banana bond.

Q: Why is the hybridization of boron in diborane sp3 and not sp2?

Even though boron has only three valence electrons, in diborane, it forms four bonds (two terminal and two bridging). This requires four hybrid orbitals, hence sp3 hybridization.

Q: Are the terminal and bridging B-H bonds in diborane identical?

No, the terminal B-H bonds are standard 2-centre-2-electron bonds and are shorter and stronger. The bridging B-H bonds are 3-centre-2-electron bonds and are longer and weaker.

Q: Why is diborane non-planar?

The two boron atoms and four terminal hydrogen atoms lie in one plane, but the two bridging hydrogen atoms lie in a perpendicular plane (one above and one below), making the entire molecule non-planar.

Question

Given below are the statements about diborane.
(A) Diborane is prepared by the oxidation of $	ext{NaBH}_4$ and $	ext{I}_2$.
(B) Each boron atom is in $	ext{sp}^2$-hybridised state.
(C) Diborane has one bridged 3 centre -2 - electron bond.
(D) Diborane is a planar molecule.
The option with correct statement(s) is

Options:

(A) (C) and (D) only

(B) (A) only

(C) (C) only

(D) (A) and (B) only

Sigma Percentile · Accepted Answer

### The Enigma of Diborane

Diborane ($	ext{B}_2	ext{H}_6$) is one of the most fascinating molecules in inorganic chemistry. It defies the traditional rules of bonding and forces us to think outside the box.

In this problem, we are given four statements about diborane, and we need to act as chemical detectives to separate the facts from the fiction. Let's break them down one by one.

### Synthesizing the Beast

Let's start with Statement (A), which talks about the preparation of diborane. How do we actually make this stuff in the lab?

The most common laboratory method involves the oxidation of sodium borohydride ($	ext{NaBH}_4$) using iodine ($	ext{I}_2$). This reaction is typically carried out in a solvent called diglyme.

The chemical equation is:

$$2	ext{NaBH}_4 + 	ext{I}_2 \xrightarrow{	ext{Diglyme}} 	ext{B}_2	ext{H}_6 + 2	ext{NaI} + 	ext{H}_2$$

As we can see, this reaction perfectly matches the description in Statement (A). **Therefore, Statement (A) is absolutely correct.**

### Unraveling the Structure

Now, let's dive into the structural statements: (B), (C), and (D). To evaluate these, we need to visualize the unique geometry of diborane.

Imagine two boron atoms. Each boron is bonded to two terminal hydrogen atoms. These terminal $	ext{B-H}$ bonds are standard 2-centre-2-electron bonds.

But what holds the two boron atoms together? They are connected by two bridging hydrogen atoms. Each $	ext{B-H-B}$ bridge is a special type of bond where three atoms share only two electrons. This is the famous **3-centre-2-electron (3c-2e) bond**, often affectionately called a "banana bond".

Since there are two bridging hydrogens, there are **two** such 3c-2e bonds. Statement (C) claims there is only one bridged bond, which is clearly false. **Thus, Statement (C) is incorrect.**

### Hybridization and Geometry

Let's look at the boron atoms again. Each boron atom is surrounded by four electron domains: two from the terminal bonds and two from the bridging bonds.

A steric number of 4 corresponds to **$	ext{sp}^3$ hybridization**. Statement (B) claims the boron atoms are $	ext{sp}^2$ hybridized, which would imply a planar, trigonal geometry. This is not the case here. **Therefore, Statement (B) is incorrect.**

Finally, what about the overall shape? The two boron atoms and the four terminal hydrogen atoms all lie in the same plane.

However, the two bridging hydrogen atoms lie in a plane perpendicular to this one—one above the plane and one below it. Because not all atoms lie in the same plane, **diborane is a non-planar molecule**. Statement (D) claims it is planar, so **Statement (D) is also incorrect.**

### The Final Verdict

After a thorough investigation, we have found that only Statement (A) holds true. The structure of diborane is non-planar, features $	ext{sp}^3$ hybridized boron atoms, and contains two 3c-2e banana bonds.

This leads us to our final answer. The option containing only the correct statement is option (b).

Select Answer:

Visualized Solution

$Preparation of Diborane$

$Hybridization of Boron$

$Bridged Bonds$

$Planarity of Diborane$

$Conclusion$

The Sigma Insight: Group 13 Elements

The Enigma of Diborane

Synthesizing the Beast

Unraveling the Structure

Hybridization and Geometry

The Final Verdict

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