Ch 13. Group 13

2

Element properties

3

Elemental forms

Boron has 3 polytypes, all contain B12 icosahedra.Two major sources of B are in the Mohave desert, Turkey.

Al to Tl All are cp metal structures (except Ga - mp 30°C, bp 2403°C)

4

Ellinghamdiagram

Al3+ is abundant in the crust, but Al is very electropositive

Al(0H)4¯ / Al E0 = −2.3 V

Reduction with C or CO requires t > 2000 °C

Al metal

5

Al (m) production by electrolysis

Na3AlF6(liq)

Hall Herault process (1888)

Al2O3 Al (m)

+e¯ , ~5V

Price $ / kg Al1852 12001886 171890 51950 0.42004 1.6

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HalidesBX3 : Lewis acidity BBr3 > BCl3 > BF3

This is the opposite of expected inductive effect

B(s) + 3/2 F2(g) BF3(g) −11093F(g) 3/2 F2(g) −3/2 D(F-F) = −233B(g) B(s) −406B(g) + 3 F(g) BF3(g) −1748

So Davg (B-F) = 583 note for comparison that D(C-F) ~ 490 kJ/mol

But ΔH (BF3(g) + F− (g) BF4− (g)) = −380

The lower LA is attributed to loss of π-bonding upon D3h Td geometry change

Only BF3 is stable in aqueous solution:BCl3 + 3H2O B(OH)3 + 3HCl

Similarly, BF4− is stable in aqu acid, but not BCl4−,BBr4

−

AlF4− Td

AlF63 − Oh (only

period 3 and higher can be hypervalent

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Borates

B(OH)3 + 2H2O → H3O+ + B(OH)4− pK ~ 9 (weak BA and LA)

B3O3(OH)4− 2 B with CN=3, 1 B with CN=4

Borate esters B(OR)3 ex: B(OCH3)3 a weak LA

8

Graphite / BN structures

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BN compoundsCl3B = :NH3 Cl3B−NH3 (s)

1/3 B3N3H3Cl3 (s) + 2 HCl (g) (trichloroborazine)

BN (s) + HCl (g)

Note: there are also cubic BN and BN analogs to fullerenes, nanotubes

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Heavier congeners

11

Borides

CaB6

AlB2

12

Borohydride clusters

13

Wade’s rules

14

11B NMR for nido [B11H14]-

15

Geometric isomers

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Cluster chemistry

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Stack compounds

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Organoaluminum compoundsAl2R6 dimeric except for large R groups

Al2R6 ↔ 2 AlR3

K ~ 10-8 for R = CH3

K ~ 10-4 for R = C4H9

K > 1 for R = C6H3(CH3)3

Al2Me6 + 2 HCl Al2Cl2Me4 + 2 CH4

+ 2 ROH Al2(OR)2Me4 + 2 CH4

preference for bridging sites is OR- ~ X- > H- > Ph- > R-

Need good e- donor and small size to bridge

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Organometallic compounds

Al(iso-C4H9)3 Al2H2(iso-C4H9)4 + 2 H2C=C(CH3)2 alkene elimination

3 Al2Cl2Me4 + 6 Na 2 Al2Me6 + 2 Al + 6 NaCl

Tl(CH3)3 Tl(CH3)2+ is linear, stable in aqu base, isoelectronic w/ Hg(CH3)2

(η5-C5H5)Tl is air stable monomeric in gas phase, chain structure in solid state

Δ

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Ziegler-Natta catalysis

½ Al2R6 + C2H4 R2Al(CH2CH2)R

R2Al(CH2CH2)R + C2H4 R2Al(CH2CH2)2R

etc..

3n C2H4 Al[(CH2CH2)n(CH2CH3]3 NaO(CH2CH2)nCH3

n C2H4 (C2H4)n (HDPE)

n CH2=C(H)CH3 (CH2C(H)CH3)n PP (isotactic)

HDPE = 50 x 106 tons/yr ≈10 lbs / person

≈500 x 106 barrels oil / yr (US consumes 720 x 106 barrels / day)

n=7-10detergents, soaps

Al2R6 H2O, NaOH

Al2Et6, TiCl4

heptane