1. DIBORANE

2. Methods Of Preparetion It is prepared by treating boron Trifluoride with LiAlH4 in diethyl ether 4BF 3 + 3LiAlH 4 2B 2 H 6 +3LiF + 3ALF 3 In a laboratory the diborane is prepared by the oxidation of sodium borobhydride with iodine 2NaBH 4 + I 2 B 2 H 6 +2NaI +H 2 In industry it is prepared by the reaction of BF3 with sodium hydride 2 BF3 + 6 NaH 450 K B 2 H 6 + 6 NaF

3. Properties 1) Diborane is a colorless, highly toxic gas. It has boiling point ok 180 K 2) Diborane catches fire spontaneously when it is exposed to atmospheric air it burns with oxygen. The reaction is exothermic releasing a lager amount of energy B 2 H 6 + 3O 2 B 2 O 3 + 3H 2 O ΔH= - 1976 K J mol -1 3) it is readily hydrolyzed by water to form boric acid B 2 H 6 + 6H 2 O 2B(OH) 3 + 6H 2

4. 4) With Lewis bases, diborane first undergoes cleavage (breaking) to form borane (BH3) which then reacts to form adducts B 2 H 6 + 2NMe 2BH 3. NMe B 2 H 6 + 2CO 2BH 3. CO 5) with ammonia an addition product B 2 H 6.NH3 which then decomposes on heating at 473K to give a volatile compound called borazole (Borazine) B 2 H 6 + NH 3 B 2 H 6. NH 3 3 B 2 H 6 + 6NH 3 473K 2B 3 N 3 H 6 + 12H 2 ( borazole) B 2 H 6 + 6NH 3 (BN) n Boron nitride

5. B undergoes sp 3 hybridization and 3 hybridized orbitals have one electron each and one orbital is vacant. Each Boron form two sigma bonds by overlapping with s orbital of H and a normal 2e2c covalent bond is formed. These are coplanar. Two more bonds are formed by overlapping of one boron sp 3 orbital with one electron, one hydrogen s orbital with one electron and another boron sp3 with no electron. Thus a 2e3c bond is formed, also called banana or tau bond. Structure B in GSES Sp 3 H 2s 2p B H H HH H H 1S

6. Types of Bonds in Boranes 1. Normal covalent bonds -2c-2e - B-H 2. Normal covalent bonds - 2c-2e - B-B 3. Bridge bonds -3c-2e - B-H-B 4. Bridge bonds - 3c-2e - B-B-B 5. Closed bridge bonds - 3c-2e - B B B Structure of Higher Boranes

7. 1. Tetraborane – B 4 H 10 Bonds – (i)Four bridging (3c-2e) B-H-B bonds viz, B 1 –H-B 3, B 2 -H – B 3, B 1 -H-B 4 and B 2 - H-B 4 (ii)One direct (2c-2e) B-B bond (B 1 -B 2 bond) (iii)Six terminal (2c-2e) B-H bonds namely B 3 -H, B 3 -H, B 2 -H, B 2 -H, B 4 -H and B 4 -H bonds.

8. 2.Pentaborane – B 5 H 9 Bonds – 1. Five terminal B-H bonds (viz., B 1 -H, B 4 -H, B 2 -H, B 3 -H and B 5 -H bonds) 2.Four bridging B-H-B bonds (namely B 1 -H-B 2, B 2- H-B 3, B 3 - H-B 4, and B 4 -H-B 1 bonds), 3. Two B-B bonds (B 1 -B 5 and B 5 -B 4 bonds) 4.One closed (3c-2e) B 5 -B 3 -B 2 bonds.

9. 3. Decaborane – B 10 H 14 Bonds – 1.Four bridging (3c-2e) B-H- B bonds namely B 5 -H-B 6, B 6 - H-B 7, B 8 -H-B 9 and B 9 -H-B 10. 2. Each of B-atoms is linked with one H-atom by terminal B-H bonds. Thus the molecule has ten terminal B-H bonds viz., B 1 -H, B 2 -H, B 3 -H, B 4 -H, B 5 -H, B 6 -H, B 7 -H, B 8 -H, B 9 -H and B 10 -H bonds. 3.Four B-B bonds (B 2 -B 5, B 2 - B 7, B 4 -B 8, B 4 -B 10 ) 4.Four closed (3c-2e) B-B-B bonds (B 1 -B 2 -B 3, B 1 -B 3 -B 4, B 1 - B 5 -B 10 and B 3 -B 7 -B 8 bonds) +

10. BORAZINE – BORAZOLE – INORGANIC BENZENE (HBNH) 3

11. PREPARATION

12. PROPERTIES