CD212 Aug 2013 Inorganic Chemistry
E. D. Jemmis, Department of Inorganic and Physical Chemistry
Indian Institute of Science Bangalore 560012
BORON SLIDES
1
Tetrahedral Carbon 1874 Van’t Hoff and LeBel
Sp3 Hybridisation
Diamond (Bragg, 1920s)
C C C
H
H H H
H
H H
H H
H
H H
C
2 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
3 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
2-D Aromaticity
Hückel’s 4n + 2 π Electron Rule
E. Hückel
2л 2л 6л
6л 6л 6л
+2 + -
+ +2
4 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Condensed Aromatics and Hückel Rule
Sp2 Hybridisation Mixed Condensation
14π 6π 10π
- + - - -
5 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
RULES OF CARBON CHEMISTRY-sp2
CARBYNE CCCCCCCCCC sp
6 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
A SIMILAR UNDERSTANDING IN THE CHEMISTRY OF BORON NEEDED
What are the modes of understanding? What are the equivalents of sp2 & sp3 hybridizations, and Hückel 4n+2 Rule? Is it possible to relate boranes to elemental boron à la benzene to graphite, methane to diamond and sp2 hybridisation to carbon nanotubes? Boron-rich solids vs boranes
7 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
REST OF THE LECTURE Molecular Chemistry of Boron compared to carbon Polyhedral Boranes and Wade’s Rule Condensed Polyhedral Boranes - mno Rule Elemental Boron and Boron Rich Solids
8 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
9
A preview of things to come - structures from boron chemistry
BB B
B
BB
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
10
B
B
C
C C
B B
B B
B B
CC
C C
- +
+2
C
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
C
CC
B
C C
C
B B
B
B
B
B B
B
BB
B
+ + +
(4n+2) π electrons The Diphenylcyclopropenyl Cation.
Ronald Breslow, Joyce Lockhart, Hai Won Chang J. Am. Chem. Soc., 1961, 83 (10), pp 2375–2379
11 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
E.D. Jemmis, G. Subramanian and G.N. Srinivas, Boron Analogs of Cyclopropenium Cation: B3H6
+, the First Three Membered Nonplanar 2π Aromatic, J. Am. Chem. Soc., 114, 7939-7941 (1992).
BB
B
+
Schulenberg, N., Wadepohl, H. and Himmel, H.-J. (2011), Synthesis and Characterization of a Doubly
Base-Stabilized B3H6+ Analogue. Angew. Chem. Int.
Ed. Engl. doi: 10.1002/anie.201104834, 2011.
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
13
C
CC
B
C C
C
B B
B
B
B
B B
B
BB
B
+ + +
CC
C
C
BB
B
B
(4n+2) π electrons
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
14
C C
CC
CC CC
CC
C
CC
C
-2
+3
+
(4n+2) π electrons
B B
B
B B
MgB2
XCC
C
CC
+
X-
acid
Stock, 1912
Masamune, 1974
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
15
CC
C
CC
+ C
C
CC
C
-
(4n+2) π electrons
- 2 e
(4n+2) electrons
B B
B
B B
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
16
B B
B
B B
C C
CC
CC CC
CC
C
CC
C
-2
+3
+
(4n+2) π electrons
XCC
C
CC
+
X-
MgB2 acid
Stock, 1912-32
Masamune, 1974
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
17
C
-1
+3
(4n+2) π electrons
CCCC C
C
C
CC
C
CC C
C
C C
+2
+
2 X-
BB B
B
BB
X
X
CC C
C
C C
Hogeveen 1975
2
Stock
MgB2 acid
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
18
+2
(4n+2) π electrons
- 2 e
(4n+2) electrons
C
C
C
C
C
C
CC C
C
C C B
B B
B
BB
BBBBBB
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Li Be B CHHH
+ 2+
3
1 58
o
o
oo
19 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
CC
C
CC
CC C
C
C C
BB B
B
BB
20 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
M
H θ2
CCOO
COθ1
n 3 4 5 6
M Co Fe Mn Cr
θ1
θ2
104.0
25.0
97.0
6.0
92.0
0.0
88.0
-3.0
M M More DiffuseLess Diffuse
CnHnM(CO)3
21 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
22
+2
(4n+2) π electrons
- 2 e
(4n+2) electrons
C
C
C
C
C
C
CC C
C
C C B
B B
B
BB
BBBBBB
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
23
+2
(4n+2) π electrons
- 2 e
(4n+2) electrons
C
C
C
C
C
C
CC C
C
C C
BBBBBB
- 2 e C C
C
C
C C
+4
B
B
B B
B
B
-2
B B
B
C
C B
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
24
The ring – cap matching becomes more crucial when there are two caps interacting from either side of the ring
HHH H
H H
Si2B4 B62- C2B4
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
25
Explanation of relative stability of positional isomers
0.0 35.3 57.1
0.0 9.7
65.8 41.5
0.0
16.6
Relative stabilization energy in kcal/mol
BB
C
C
BBB
B
B
C
CB
B
B
B
CC
C
B
C
BB
BB
B
B
CCB
BBB
B
B
CC
BB
B
B
C
BC
BB B
C
C
B B
B
C
C
B B
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
BB B
B
BB
BB
B
BB B
BB B
B
B B
B B
B
B BB
26 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
26.6
24.2
27 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
COMMONLY FOUND BORANES ARE BASED ON POLYHEDRA. ICOSAHEDRAL B12H12
-2 MOST FAVOURED.
ELEMENTAL BORON HAS MOSTLY ICOSAHEDRAL UNITS
BnHn-2
28 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Longuet-Higgins 1955
B12H12-2
29 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Synthesis, Structure, Bonding, Reactions, Theoretical Studies
styx formalism to predict the structure of boranes s # BHB 3c-2e t # BBB 3c-2e y # BB 2c-2eh x # BH 2c-2e BpHp+q s=p-t, x=q-s, 2y=s-x
W. N. Lipscomb 30 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science,
Bangalore
Rudolf Diagram
R. E. Williams
31 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Wade’s n+1 Skeletal Electron Pair Rule
Mol Formul
a
n ep
BH CH
ep q
B12H12 12 13 12 0 12 -2
B11H11 11 13 11 0 11 -4
C2B9H11 11 13 9 3 12 -2
C3B8H11 11 13 8 4.5
12.5
-1
n + 1 n + 2
Wade, Williams, Mingos, Rudolf
H
H H
n
2n
n-1
n
32 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
C6H6 C6H6+2
C4B2H6 B6H10
C6H6+4
C2B4H6 B6H6
-2
The Organic Connection
33 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
34 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
35 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
36 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
37 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
COMMONLY FOUND BORANES ARE BASED ON POLYHEDRA. ICOSAHEDRAL B12H12
-2 MOST FAVOURED. THIS IS CHANGED WHEN OTHER ELEMENTS ARE INTRODUCED. THE BRICKS ARE NOT THE SAME.
BnHn-2
38 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
39
Structure of some commonly found polyhedral boranes
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
40
1. M(R)-C2B4H6 a) Ga(CH3)-2,3-C2B4H6 b) Ga(CMe3)-2,3-(CSiMe3)2B4H4 (c) Ga(CMe3)-2,4-(CSiMe3)2B4H4 d) Ga(C10N2H8)(tBu)-2,3-(CSiMe3)2B4H4. 2C6H6 e) Ga(C10N2H8)(tBu) -2,4-(CSiMe3)2B4H4. 2C6H6 f) Ga(C8N4H6)(tBu)-2,4-(CSiMe3)2B4H4 g) Ga(Cl)(CH2NMe2)2-2,3-(CSiMe3)2B4H4.C6H6 h) Ga(Cl)(CH2NMe2)2-2,4-(CSiMe3)2B4H4.C6H6 i) In(CH3)-2,3-C2B4H6 j) In(CHMe2)-2,3-(CSiMe3)B4H4 k) In(CHMe2)-2,4-(CSiMe3)B4H4 l) In(C10N2H8)(CHMe2)-2,3-(CSiMe3)2B4H4 m) In(C10N2H8)(CHMe2)-2,4-(CSiMe3)2B4H4 n) In(C8N4H6) (CHMe2)-2,3- (CSiMe3)2B4H4
CBBBGaBC
CB
B
B
Ga
BC
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
41
2. M(R)-C2B9H11 a) Ga(C2H5)-2,3-C2B10H11 b) [Al (Me) B11H11]2-. [AsPh3]2 c) Al(Me)-2,3-C2B9H11 d) Al(C2H5)-2,3-C2B9H11 e) Al(Me)2-2,3-C2B9H11 f) Al(Et)(PEt3)2-2,3-C2B9H11 g) Tl-2,3-C2B9H11. PPh3
CBBBGaBC
BB
C B
B
B
BB
Ga
C
B
B
Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Elemental boron - B12 units Condensed polyhedral Boranes What are the electronic requirements? Electron Counting Rules for Condensed polyhedral boranes
42 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
B12H12-2
N+1 electron pairs - Wade
B20H16
B30H24
43 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
The mno Rule for Polycondensed Boranes, Metallaboranes, and Metallocenes
m+n+o skeletal electron pairs m à number of polyhedra n à number of vertices o à number of single atom bridging
44 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
m+n+o = 2+21+0 = 23 ep 18BH + 3B à 18+4.5 = 22.5 ep -1 charge B12H12
2- m=1, n=12, o=0 à Wades n+1 Rules
B21H18-
m = # polyhedra n = # vertices o = # single atom bridges
45 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
B30H24 m+n+o = 3+30+0 = 33 ep 24BH + 6B à 24 + 9 =33 ep.
neutral
46 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
m + n + o =2 + 20 +0 = 22ep 16BH + 4B 16 + 6 = 22ep, Neutral
Synthesised 40 years ago by Lipscomb and Muettertties. Neutral Molecule.
B20H16
47 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Co(C2B9H11)2-1
3 + 12 + 36 +1 = 52 e
m+n+o2+23+126 epairs52e
Examples for Single atom bridge (single vertex sharing)
48 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
C & E News
49 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
B19H22-1 and
not B19H20-1
m+n+o = 2+19+0+2 = 23ep
(BH)17B2H3- =
17+3+1.5+0.5 = 22ep
J. A. Dopke, D. R. Powell, D. Gaines, Inorganic Chemistry, 39, 463 (2000), J. T. Spencer etal, Inorg. Chem. Commun. 5, 274, (2002).
The two electron deficiency is not noticed because it was not anticipated. The X-ray structure was refined assuming B19H20
-.The Mass spectra gave
consistently two mass units higher than calculated. The structure should be B19H22
-
50 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
B12H16 B13H19
B16H20 B18H20
2-
n-B18H22 iso-B18H22
51 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
52 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
53 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
54 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
55 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
C6H6 C6H6+2
C4B2H6 B6H10
C6H6+4
C2B4H6 B6H6
-2
The Organic Connection
56 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Hückel 4n+2 p Electron Rule A subset of the mno Rule
B14H12 -2, two hexagonalbipyramids sharing an edge
m+n +o =2+14 =16ep 12(BH) + 2B =12+3 =15ep -2 charge
57 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
m+n+o+p = 2+12+0+2 = 16 ep 10(BH) +2(B) = 10+ 3 = 13ep -6 charge
m+n+o+p = 2+10+0+4=16ep
8(BH) +2B =8 + 3 =11ep -10 charge
B12H10-6, C4B8H10
-2
B10H8-10 ,C10H8
(4n+2)π =10e + 22 C-C bonding electrons =16ep 58 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science,
Bangalore
26.6
24.2
-2
59 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
If Buckminster Fuller had his way, boron would have the structure
Everything in the universe seems to be made up of icosahedron, including viral capsids.
60 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Even the universe is of icosahedral symmetry?
61 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
α-Rhombohedral Boron - B12
6 borons from 2c-2e B-B bonds 6 borons from 3c-2e B-B-B bonds. This leaves 6-(2/3)6 = 2 electrons for the B12 skeletal bondings
62 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
Ideally elemental boron should have each B12 surrounded by 12 B12 , but this creates problem in space filling; this is present in Y24B1584 but with many defects. (YB66)24 will not be discussed today - we do not understand it enough. Structure of beta-rhombohedral boron and related slides will be in another presentation.
63 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
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