A SEMINAR ON BORANES AND CARBORANES.pptx

A Seminar topic on Boranes and Carboranes.

1. PRESENTED BY Name:-Muktikanta Samal Roll No:-CH/12/23 M.Sc. 3 rd Semester Department of Chemistry Fakir Mohan University, Balasore BORANES AND CARBORANES A SEMINAR ON

2. CONTENTS:- Introduction Methods Of Preparation Bonding and Structure in Boranes Types of Boranes Carboranes Types Of Carboranes Wade’s Rule Applications Conclusion

3. INTRODUCTION:- The binary compounds of boron and hydrogen are called boranes. Boranes were first prepared between 1912 and 1936, by Alfred Stock. The molecules of these compounds are electron deficient. The parent member BH 3  is called borane. All boranes are diamagnetic and colourless and highly reactive.

4. General formula is B X H Y The number of boron atoms in a compound is indicated with prefixes of Latin such mono-, di, tri-, etc. The Latin prefixes are used before borane. The number of hydrogen atoms in boranes is written in Arabic numeral. These numeral is enclosed in parenthesis. Ex:- BH 3 = Borane(3) , B 2 H 6 = Diborane(6) , B 5 H 11 = Pentaborane(11)

5. Methods of Preparation:- When Magnesium Boride(Mg 3 B 2 ) reacts with dil. HCl, Then it gives mixture of boranes, magnesium salt of the acid and H 2 . This method is known as Stock’s method. 2Mg 3 B 2 + 12HCl 6MgCl 2 + B 4 H 10 + H 2 When Boron trichloride(BCl 3 ) reacts with hydrogen gas(H 2 ) at low pressure, the formation of Diborane takes place as the result of the reduction. 2BCl 3 + 6H 2 B 2 H 6 + 6HCl

6. BONDING AND STRUCTURE IN BORANES:- In Boranes 4 types of bonds are present 3c-2e B-H-B 3c-2e B-B-B 2c-2e B-H 2c-2e B-B For e.g. Diborane Diborane is a compound of two atoms of boron, and with these two atoms of boron, six atoms of hydrogen are also present. Two hydrogen bridges are present. Each boron atom is present in sp 3 hybridization, that means boron atoms have four hybrid orbitals.

7. The diborane molecule has 2 type of bonds. 1. four terminal (2c-2e) B-H bonds. 2. two bridged (3c-2e) B-H-B bonds. Four terminal (2c-2e) B-H bonds Each of these bonds are formed by sharing of 2 electrons between boron and terminal hydrogen atoms. It’s a normal covalent bond. 2. two bridged (3c-2e) B-H-B bonds Each of these bond is formed by sharing of 2 electrons between 2 B and 1 H atoms . It is also called as banana bond.  

8. TYPES OF BORANES:- 1. CLOSO BORANES:- Closed, triangulated polyhedra structure. All corners of triangulated polyhedra are occupied. General formula: B n H n+2 Example: B 6 H 8 , B 4 H 6

9. 2. NIDO BORANES:- Nido boranes are formed when one corners of the polyhedra is removed. Nest like, non-closed structure. General formula: B n H n+4 Example: B 5 H 9, B 2 H 6

10. 3. ARACHNO BORANES:- These boranes are formed when two corners of the polyhedra is removed . Web like ,non-closed polyhedra structure. General formula: B n H n+6 Example: B 4 H 10 , B 9 H 15

11. 4 . HYPhO BORANES:- Hypo- net like structure. These have most open clusters of borane. General formula: B n H n+8 These boranes are having complex structures. Example : B 8 H 16 , B 10 H 18 These boranes formed by linking of two or more other type of boranes. These structures are very complex. General formula : B n H n+10 5 . CONJUnCTO BORANES:-

12. CARBORANES:- Carboranes are mixed hydrides of boron and carbon in which carbon and boron atoms occupy the vertices of triangulated polyhedron. Carboranes are most important heteroboranes. Carboranes are member of a class of organometallic compounds containing carbon (C), boron (B), and hydrogen (H). General formula of carboranes is C 2 B n H n+m , where m is an integer. Boranes and carboranes have same number of electrons in their bonding framework , will have similar structure.

13. TYPES OF CARBORANES:- CLOSO CARBORANES:- Closed-cage structural arrangement of the carbon and boron atoms where all boron and carbon atoms occupy all vertices of the polyhedron . General formula: C 2 B n H n+2, Example:- C 2 B 8 H 10

14. One corner of triangulated polyhedra is removed. It’s structure is “nest” like appearance. General formula: C 2 B n H n+4, Example- C 2 B 4 H 8 , [C 2 B 9 H 12 ] - NIDO CARBORANES:- ARACHNO CARBORANES:- Two corners of triangulated polyhedra is removed. General formula: C 2 B n H n+6, Example- C 2 B 7 H 13

15. WADE’S RULE :- This rule provides electron counting rule useful for predicting the structure of boranes and carboranes. Structure H atoms (n+m) Closo n+2 Nido n+4 Arachno n+6 Hypho n+8 Conjuncto n+10 n= number of boranes m= number of excess hydrogens (m= total H - n) Count boranes, n Then count hydrogen (H) If charge is there, count as hydrogen one negative charge = one hydrogen 4. Find excess of hydrogen (m= H - n) 5. Predict n+m If other atoms are present like C, N, O, etc Then Element Equivalent B Group(B, Al,Ga,In, Tl) B C Group(C, Si, Ge, Sn, Pb) BH N Group(N, P, As, Sb, Bi) BH 2 O Group(O, S, Se, Te, Po) BH3 Count Valence electron = write B + Hydrogen atom

16. For example:- C 2 B 7 H 11 =(BH) 2 B 7 H 11 (C=BH) =B9H13 n=9 Total hydrogen= 13 Excess Hydrogen (m) = total H – n = 13 – 9 = 4 hydrogen = n + m = n + 4 For n+4 , The structure is Nido.

17. APPLICATIONS OF BORANES AND CARBORANES:- Boranes are used as rocket fuels in supersonic aeroplanes. Used as catalyst in polymerisation reaction. Used as reducing agent in organic reactions. Boranes can be used as vulcanising agent for natural and synthetic rubber. Carboranes are used in cancer drug development.

18. CONCLUSION:- Boranes are colourless and gaseous at room temperatures. Boranes are highly reactive and reacts violently with water. In boranes 3c-2e bonds are present; It is unique type of bond present in boranes only. Carboranes are mixed hydrides of boron and carbon. And have same structure like boranes. Carboranes derived from pyrolysis of boranes.