DIBORANE-PREPARATION:

Boranes are hydride of Boron and diborane is famous borane. It is gas and is highly inflammable in air and poisonous Diborane is used for preparing substances such as high energy fuel and propellants.

Other Methods:

Structure of “Borazine/Borazole”/inorganic Benzene:

(1) Borazine is an inorganic compound with the chemical formula  (B₃N₃H₆).and also called Borazole. It is a heterocyclic compound, containing the 3-(BH) units and 3-(NH) units alternate.

(2) Borazine formed by reaction of B₂H₆ and NH₃ in the ratio of 1:2 at room temperature.

(3) Borazine is isoelectronic and isostructural with benzene. For this reason borazine is known as “inorganic benzene”. Like benzene borazine has delocalized electrons and aromatic character. And it is a colourless liquid.

(4) In Borazine molecule nitrogen is more electro negative than the boron. Nitrogen acquires partial negative charge and boron acquires partial positive charge and back bonding take place between boron and nitrogen.

(5) As compared with Benzene, Borazole/borazine is less stable and more reactive toward Electrophilic Aromatic Substitution reactions due to presence of polar B-N bond in it while in benzene all the C-C bonds are non polar.

(6) Borazine is a highly polar molecule due to high Electronegativity difference between Boron and Nitrogen.

Even though Borazine/Borazole  and Benzene have same stricture their chemical properties are different.

(1) Organic benzene is C₆H₆ while Inorganic benzene is Borazine having chemical formula B₃N₃H₆

(2) The pi bonds in borazine are highly polarized than pi bonds in benzene due to high polarity (B-N polar bond) of Borazine molecules. Thus borazine is more nucleophillic (Negative) hence more reactive than benzene with respect to “Electrophic addition reactions”.

Here protonation(H⁺) take place at nitrogen atoms due to more electron density (more negative)  and  chlorine attack at boron atoms.

(3) Aromaticity of borazine is less than benzene because some delocalization in Borazine/Borazole is not complete as benzene. One reason is that nitrogen atom has more electronegativity than boron ,the electron density is higher at nitrogen atoms then boron. The electron density is determined by both sigma and pi bonds, both of which have polarity, but opposite directions,   hence it is less reactive  toward “Electrophilic  substitution reactions” than Benzene. 

(4) Borazine undergo polymerization when strongly heated under vacuum and yield biborazonyl and naphthazine whose structure are similar to biphenyl and naphthalene.

Structure of "Borazon" (Cubic boron nitride):

Structure of "Inorganic Gaphite";

Related Questions: 

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why Ga has small size than Al exceptionally

Why aqueous solution of borax reacts with two moles of acids ?

What is structure of solid Ortho Boric acid ?

What is the structure of trimetaboric acid and trimetaborate ion?  

Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?

Why Borazine (B3N3H6) is also known as inorganic benzene ?.

Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.

Why B-F do not exist as dimer?. Explain.

Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?

Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?

Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:

What is the molecular formula of Borax ?

What is the difference between the structure of AlCl3 and diborane?

STRUCTURE OF DIBORANE :

(1)  B₂H₆ contains 4-Terminal H are bonded by Sigma bond and  remaining 2-H are bridging hydrogen’s and of these are broken then dimer become monomer.

(2) Boron undergoes sp3 hybridisation 3 of its sp³ hybridised orbitals contain one( e¯) each and fourth sp³ hybrid orbital is vacant.

(3) 3-(Three) of these sp³ hybrid orbitals get overlapped by s orbitals of 3-hydrogen atoms.

(4) One of the sp3 hybrid orbitals which have been overlapped by s orbital of hydrogen gets overlapped by vacant sp³ hybrid orbital. Of 2^nd Boron atom. And it’s vice versa.

(5) By this two types of overlapping take place 4 (sp3– s) overlap bonds and 2(sp² – s – sp³) overlap bonds.

(6) H is held in this bond by forces of attraction from B and This bond is called 3 centred two electron bonds (3C-2e bond) . Also called Banana bonds. Due to repulsion between the two hydrogen nuclei, the delocalised orbitals of bridges are bent away from each other on the middle giving the shape of banana.

(7) The two bridging hydrogens are in a plane and perpendicular to the rest four hydrogen..

ILLUSTRATED EXAMPLE (1): In Diborane

(A) 4 bridged hydrogens and two terminal hydrogen are present

(B) 2 bridged hydrogens and four terminal hydrogen are present

(C) 3 bridged and three terminal hydrogen are present

(D)None of the above

ILLUSTRATED EXAMPLE (2): Which one of the following statements is not true regarding diborane?

(A) It has two bridging hydrogens and four perpendicular to the rest.

(B) When methylated, the product is Me₄B₂H₂.

(C) The bridging hydrogens are in a plane and perpendicular to the rest.

(D ) All the B–H bond distances are equal

ILLUSTRATED EXAMPLE (3): The structure of diborane (B₂H₆) contains

(A) Four (2C–2e–) bonds and two (2C–3e–) bonds

(B) Two (2C–2e–) bonds and two (3C–2e–) bonds

(C) Four (2C–2e–) bonds and four (3C– 2e–) bonds

(D )None of these

ILLUSTRATED EXAMPLE (4): The molecular shapes  of diborane is shown:

Consider the following statements for diborane:

1. Boron is approximately sp3 hybridised

2. B–H–Bangle is 180°

3. There are two terminal B–H bonds for each boron atom

4. There are only12 bonding electrons available

Of these statements:

(A ) 1, 3 and 4 are correct                  (B) 1, 2 and 3 are correct

(C) 2, 3 and 4 are correct                    (D) 1, 2 and 4 are correct

STRUCTURE OF DIAMOND :

(1) Each carbon is linked to another atom and there is very closed packing in structure of Diamond.

(2) Density and hardness is very much greater for diamond because of closed packing in diamond due to sp3 hybrid and are tetrahedrally arranged around it. And C-C distance is 154pm

(3) Diamond has sharp cutting edges that's why it is employed in cutting of glass.

(4) Diamond crystals are bad conductor of electricity because of absence of mobile electron.

(5) 1 carat of diamond = 200 mg.

(6) Diamond powder if consumed is fatal and causes death in minutes.

STRUCTURE OF GRAPHITE:

(1) In Graphite Carbons are sp² hybridised out of the four valence electrons, three   involved in (sp²-sigma) covalent bonds form hexagonal layers and fourth unhybridised p– electron of each carbon forms an extended delocalized p-bonding with carbon atoms of adjacent layers

(2) Each carbon is linked with 3 carbons and one carbon will be left and form a two dimensional shed like structure.

(3) Distance between two layers is very large so no regular bond is formed between two layers. The layers are attached with weak vander waal force of attraction.

(4) The carbon have unpaired electron so graphite is a good conductor of current.

(5) The C-C bond length within a layer is 141.5 pm while the inter layer distance is 335.4 pm shorter than that of Diamond (1.54 Å).

(6) Due to wide separation and weak interlayer bonds, graphite is sift , greasy and a lubricant character and low density.

(7) Graphite marks the paper black so it is called black lead or plumbago and so it is used in pencil lead.

(8) Composition of pencil lead is graphite plus clay .the percentage of lead in pencil is zero .

 (9) Graphite has high melting point so it is employed in manufacture of crucible.

(10) Graphite when heated with oxidizing agents like alkaline KMnO4 forms mellatic acid 

                                                 (Benzene hexa carboxylic acid).

(11) Graphite on oxidation with HNO₃ gives acid i.e. known as Graphite acid C₁₂H₆O₁₂