Understanding B2H6 (Diborane)

B2H6, commonly known as diborane, is a chemical compound containing boron and hydrogen. It is a dimer of BH3. Diborane is an important reagent in organic chemistry and is known for its unique structure involving 3-center-2-electron bonds.

Analyzing Statements about B2H6 Molecule

Let's evaluate each given statement regarding the B2H6 molecule to determine its correctness.

Statement A: B2H6 Synthesis

Statement A says that the addition of Et2O•BF3 to NaBH4 in a polyether solvent produces B2H6. This is a common laboratory method for the synthesis of diborane. Sodium borohydride (NaBH4) acts as a source of hydride ions, and boron trifluoride etherate (Et2O•BF3) provides the boron. The reaction proceeds as follows:

\(3\text{NaBH}_4 + 4\text{BF}_3 \xrightarrow{\text{Ether solvent}} 2\text{B}_2\text{H}_6 + 3\text{NaBF}_4\)

This statement is correct.

Statement B: B2H6 Symmetry

Statement B claims that B2H6 has D2d symmetry. The structure of diborane involves two bridging hydrogen atoms and four terminal hydrogen atoms. The two boron atoms and the four terminal hydrogen atoms lie in one plane, while the two bridging hydrogen atoms lie in a plane perpendicular to the first plane, symmetrically positioned above and below the B-B axis. This structure possesses a center of inversion. The correct point group symmetry for diborane (B2H6) is D2h, not D2d. The D2d point group lacks a center of inversion, which is present in B2H6.

This statement is incorrect.

Statement C: B2H6 Reaction with NMe3

Statement C states that the reaction of B2H6 with NMe3 gives Me3N•BH3. Trimethylamine (NMe3) is a strong Lewis base. Diborane reacts with Lewis bases, undergoing cleavage. Strong Lewis bases like NMe3 cause symmetric cleavage of the diborane dimer, forming adducts with the monomeric borane (BH3) unit.

\(\text{B}_2\text{H}_6 + 2\text{NMe}_3 \rightarrow 2\text{Me}_3\text{N} \cdot \text{BH}_3\)

This statement is correct.

Statement D: B2H6 Magnetic Property

Statement D claims that B2H6 is diamagnetic. A substance is diamagnetic if all its electrons are paired. Boron has 3 valence electrons, and hydrogen has 1. In B2H6, all 12 valence electrons (2×3 + 6×1) are involved in bonding, including the terminal B-H sigma bonds and the bridging 3-center-2-electron B-H-B bonds. All these electrons exist as pairs. Since there are no unpaired electrons in the B2H6 molecule, it is diamagnetic.

This statement is correct.

Conclusion on B2H6 Statements

Based on the analysis:

• Statement A is correct (Synthesis).
• Statement B is incorrect (Symmetry is D2h).
• Statement C is correct (Reaction with NMe3).
• Statement D is correct (Diamagnetic property).

Therefore, the correct statements for the B2H6 molecule are A, C, and D.