Diborane Structure

Diborane is defined as a chemical compound which consists of hydrogen and boron, with the formula B2H6. It is prophetic gas and colourless with a repulsively sweet odour. Diborane synonyms include boron hydride, bromoethane and die borohydride. Boron’s key compound is diborane with a variety of applications. Diborane has attracted wide attention for its electronic structure and its derivatives are also very useful reagents. 

It can be basically defined as a structure made up of boron and hydrogen atoms. This substance is said to be highly unstable at room temperature with a sweet odour. The compounds which consist of boron and hydrogen atoms are called boranes. One of the simplest boron hydrides is diborane. 

The boron hydride when mixed well with the air forms an explosive mixture. At room temperature, this substance can ignite easily. An extensive study of this particular substance has led to the development of multiple syntheses. The initial reaction of hydrides donors with boron halides or alkoxide mostly preparation takes this. The diborane industry synthesis of diborane involves the reaction of BF3 by sodium hydride, lithium aluminium hydride or lithium hydride.


Bonding and Structure

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The diborane structure has D2h symmetry. Four of the hydrides are terminal, while two others bridge between the boron centres. The B-H bridge bond and the B-H terminals are 1.33 and 1,19 Armstrong respectively. This bond length difference reflects the difference in their strengths and the B-H bond being relatively weaker.

The weakness of the B-H terminal and B-H bond is indicated by their vibrational structures in the infrared spectrum being approx 2100 and 2500 cm. The molecular determined theory determines the bond between boron and the terminal hydrogen atoms as two centres and two electron covalent bonds. 


The bonding between the bridging hydrogen atom between the boron atoms is however different from that in molecules such as hydrocarbons. For bonding to terminal hydrogen atoms, each boron uses two electrons and has one valence electron remaining for additional bonding. The bridging hydrogen atoms provide one electron from each of them. These types of bonds sometimes form banana bonds.


History

In the 19th century, diborane was first synthesised by hydrolysis of metal boroids but it was never analysed. From 1912 to 1936, the major pioneer in the field of chemistry of boron hydride Alfred Stock undertook his research which led to the method for the handling and synthesis of the higher volatile, reactive and often toxic boron hydride.

He proposed the first ethane like diborane structure electron diffraction measurement by S.H Bauer, who initially appeared to support his structure. Because of the structure of L. Pauling, H.I Schlessinger and A.B  Burg did not specifically discuss 3 centres and 2 electrons in their classic reviews earlier in early 1940.

However, the review does discuss the bridged structure of D2h in some depth. It is to recognise that this formulation easily accounts for many diborane properties.

Longuet Higgins in 1943, when he was still an Oxford undergraduate, was the first man to explain the bonding and structure of the boron hydrides.


Reactions

Diborane is a versatile and highly reactive reagent. Diborane dominating reactions pattern involves the formation of adducts with sluice base. Such initial adducts often proceed rapidly to give other products. Borane reacts with ammonia to form the diammoniate of diborane, DABA with the lesser quantity of ammonia borne depending on conditions used. 

It also readily reacts with alkanes to form substituted alkanes products which will readily undergo further addition reaction. Borane as a pyrophoric substance it reacts exothermically with oxygen to form water and boron trioxide so much that it was considered as a possible ramjet propellant or a rocket but discarded because back then it was very dangerous to handle and expensive. 

2B2H6 + 6O2 2B2O3+ 6H2O

Diborane also reacts with water violently to form hydrogen and boric acid. 

B2H6 + 6H2O2B(OH)3 +6H2.


Uses

As a rocket propellant diborane has been tested, the complete combustion is considered as strongly exothermic. In the rocket engine, however, the combustion is not complete, as some boron monoxide BO is produced. These incomplete combustion mirrors of hydrocarbons produce carbon monoxide CO. as rubber vulcanizer also diborane is used as a catalyst for hydrocarbon polymerization, as a doping agent for the semiconductor production of highly pure boron for semiconductor production. It is also used to colour or coat the walls of tokamaks to reduce the amount of the impurities of the heavy metal in the core amount of plasma. 

The diborane toxic effects are primarily due to the irritant properties.

A short term exposure to diborane can cause a feeling of tightness of chest and shortness of breath, wheezing and coughing. These symptoms and signs can occur immediately or be delayed up to 24 hours. Eye and skin irritation can also occur. Animal studies have shown that diborane causes the same type of effects which are observed in humans.

FAQ (Frequently Asked Questions)

Q1. What is the diborane deficiency of Electrons?

Ans: Diborane is said to be electron deficient structure as boron requires 5 electrons to complete its octet. But in this molecule, each atom of boron is bonded with 2 terminal hydrogen atoms each. Also, both the boron atoms are held together by two hydrogen atoms. Therefore, it is known as an electron-deficient molecule.

Q2. What is the significance of Diborane?

Ans: There are many uses of diborane. It is used as a rocket propellant, as a reducing agent, like a rubber vulcanizer, as a catalyst for hydrocarbon polymerization, as a flame-speed accelerator and as a doping agent as well. It is used in electronics to impart electrical properties in pure crystals.

Q3. Which type of bonds is present in Diborane?

Ans: B2H6 forms covalent banana bonds and are also known as three centres and two electron bonds. In the diborane atom, two types of H atoms are present. The hydrogen terminal atoms form covalent bonds with B which are normally two centres and two electron bonds. The H bridged atom forms a banana bond of three centres and two electron bonds.

Q4. What is Diborane’s Formula?

Ans: B2H6 is the formula of diborane.