Greenwood & Earnshaw
2nd Edition
Chapter 7
Aluminium, Gallium,
Indium and Thallium
Observations
Aluminum is the most common metal, 8.3% wt.
of the earth’s crust. Ga, In, Tl are relatively rare.
Aluminum is monoisotopic, excellent heat and
electrical conductor.
Gallium has anomalous melting point (but not
boiling point) and anisotropic electrical resistivity:
a 17.5, b 8.20, c 55.3; liquid is 25.8 F ohm-cm.
Thallium has a very stable oxidation state of one
and is very electropositive, corrodes in moist air.
I : III oxidative equilibria dominates its chemistry.
The Trihalides of Aluminum
polymeric solids, CN = 6, µ X || dimeric CN = 4, 2 µ X
Halides once hydrated cannot be dehydrated. AlF3 alone
does not form a hexahydrate.
AlCl 3
H2O
[Al(H2O)6]3+ 3 Cl -
AlF3
H2O
AlF3C nH2O n = 1, 3, 9
heat
AlO(OH)CCH2O + 3HCl
heat
Al 2O3
the affinity of Al for F ≅ O
1
Complex Halides – Cryolite Structure
AlF3 + 3 NaF
Aluminum Smelting
Na3AlF6
Synthetic cryolite has the perovskite structure (CaTiO3) a face-centered cubic
structure. No AlF63- ions occur. The is not clearly ionic since the Na-F and
Al-F distances are nearly equal. All Al occupy octahedral sites; 1/3 Na occupy
octahedral sites, 2/3 occupy 12 coordinate sites.
Trihalides of Ga, In, Tl & Complex Halides
The trichloride of Al is important as Friedal Crafts & isomerization Catylist.
The trihalides of Ga resemble those of Al with some structural differences.
The trihalides become less stable as one goes down the group.
103.9E
E
GaCl4
InCl 4
-
Cl
2-
242 pm
Td
Other adducts vary
between sq. pyd. &
trig. bipyd. geometry.
Cl In Cl
Cl 246 pm Cl
InCl52-
square pyramidal
The trihalides of Tl are chemically quite distinct from the rest of the group.
H2O
TlF3
mpd 550 C
[Tl 2Cl 9]3-
NaTlF4 Fluorite Str.
Na3TlF6 Cryolite Str.
Tl(OH)3 + 3 HF
hydrolyses rapidly
Two regular TiCl6 octahedra sharing a common face.
Cl
Ga(II) ~ In(II)
vs. Ga(I)Ga(III)
@2dioxane
Ga
Cl
Cl
Tl(I)
Cl
vs
Ga+[GaCl4]-
Tl(III)
is Tl
TlI3
+
-
Cl
Cl
Ga
Cl
Cl
Ga
2-
Cl
Ga
Cl
-
+
but TlI4 is Tl(III); Tl 2I4 is Tl TlI4
I3
Hydrates, Hydroxides and Oxides
Acidity of
[M(H2O)6]3+
B(OH)3
Al
4.95
M
pKa
In
3.7
Ga(OH)3
Amphoteric
~100 C
MO(OH)
layer lattice
~150 C
In(OH)3
TlOH
Basic
Strongly Basic
~KOH
100-1500 atm H2O
~100 C
250-400 C
InO(OH)
~Rutile Str.
Tl2O
black platelets
- O2 ~1000 C
M2O3
In2O3
structurally
very complex
See p 243 text
Basic
SiO2
CaO
Al 2O3
Ca(AlO2)2
Base
Acid
Oxide Acceptor
Oxide Donor
Al 2(SiO3)3
Tl *
1.15
* Needs "non-coordinating anion"
Al(OH)3
Acidic
Ga
2.6
Tl 2O3
OH-
Tl3+
2
Important Aluminum Oxides
α
α-Alumina – Al2O3 – Corundum, Sapphire
including very strong optical glass, “Saffil” fibres.
γγ-Alumina – Al2O3 – “Activated alumina”, a
defect spinel structure.
Sodium-β
β-alumina – NaAl11O17 - Na2O @0.11Al2O3
–a “solid electrolyte” & Na+ conductor, see Na/S
battery applications, p 678 text.
Tricalcium Aluminate – Ca3Al2O6 – Principal
ingredient of “Portland Cement”.
Complex Metal Hydrides
H
H
H
H
H
Al(BH4)3
H
70E
EC
B
H
H
B
H
Al
B
H
H
H
H
H
B
H
H
H
B
H
fluxional
H
H
H
N(CH3)3
H
Al
H
H
H
B
H
H
H
H
B
H
Al
H
H
H
H
H
H
H
H
H
H
B
N(CH3)3
B
- B2H6
H
H
H
H
Al
B
H
Al
H
H
Al2Me6
H
B
CH3
H
H
B
Hydrides: Al, Ga, In, & Tl
Al
+
no reaction
3 /2 H 2
4 AlH3(Et2O)n + 3 LiCl
4 AlCl 3 + 3 LiAlH4
benzene
α-AlH3 has 6 Oh 3c-2e µ-H's
reflux
6 dAl-Al = 324 pm, 6 dAl-Al = 445 pm,
E, no Al-Al bonding.
pAlHAl = 141E
4 AlH3
Td 150-200E
EC
H
(CH3)3N
Al
H
2 N(CH3)3
N(CH3)3
H
GaH3@NMe3
LiGaH4 + Me3N@@HCl
Hydrides of In, Tl too unstable to isolate
LiMH4 M =
EC Tdec =
B
Al
380E
E 100E
E
Ga
50E
E
In Tl
BF3
GaH3
Viscous liq.
Tmp -15E
EC
Tdec ~25E
EC
OE
E
3
Al, Ga, In, & Tl -- Alkyls & Hydrides
3/ 2
Al +
H2 + 2 AlR3
3 AlR2H
+ H2C CH2
AlEt2H
200 atm
CH2 100EEC
2
cat. amts.
Al[CH2CH(CH3)2]3
2 Al + 3 H2 + 6 (CH3)2C
2 Al(CH2CH(CH3)3
6 H2C
6 Et2AlH
2 Al + 3 H2 + 2 Al2Et6
Na
cf. Hydroboration
AlH3 ineffective
AlEt3
dimeric
dimeric
CH2
3 Al2Et6
Al[CH2CH(CH3)2]3
monomeric
Al[CH2CH(CH3)2]3
(CH3)3CHCH2)3Al
2-
mp 40E
EC, diamagnetic
TlX3 + 2 RMgX
R
Tl
+
R
X-
linear cation, isoelectronic with R2Hg
R = Me, soluble and stable in water.
Aluminum Alkyls – The “Growth” Reaction
H2C
CH2
150E
EC
100 atm
AlEt3
Et2AlCH2CH2Et
H2C CH2
150E
EC
100 atm
(CH2CH2)xEt
(CH2CH2)yEt
(CH2CH2)zEt
Al
CH2CH2
H2C CH2
H2C
Al
Et
Et
CH2
Et
Al
Al
Et
Et
Et
Et
H2C
CH2CH2Et
Al
CH2CH2Et
Et
Et
CH2
Al
CH2
Al
CH2
Et
CH2
CH2CH2Et
CH2
Et
Et
CH2
Et
Et
CH2
Et
etc
Aluminum Alkyls – Ziegler-Natta Catalysis
alkane
solvent
TiCl4 + Al 2Et6
H2C CH2
LnTi
Et
H2C
CH2
H2C CH2
LnTi
LnTi
LnTi-Et
Ti(III)EtnCl3-n
brown suspension
Classical Mechanism:
CH2CH2
Et
LnTi
LnTi CH2
CH3
CH2CH3
CH2CH2
Etc.
CH2CH2
LnTi
H2C CH2
CH2CH3
H2C CH2 CH CH
2
3
H2C
CH2CH2
LnTi
LnTi CH2CH2
H2C CH2
CH2CH2
or
Et
CH2
H2C CH2
H2C
CH2CH3
CH2
CH2CH2
LnTi
CH2CH3
H2C CH2
4
Aluminum Alkyls – Ziegler-Natta Catalysis
Classical mechanism requires chain transfer of
an ever increasing length chain, entropy
consideration as polymer chains become very long.
The “concerted pathway” was invoked to counter
the entropy troubles above.
Polypropylene is only “head-to-tail”, most
valuable polymer produced by Z-N catalysis. The
methyl groups alternate along the chain.
Reactivity: terminal > geminal > internal olefins.
Only homopolymerization feasible.
Some Interesting Organometallics
Tl
241 pm
TlOH(aq) + C5H6
Tl
Tl
Trialkyl derivatives of Ga, In, Tl
are all monomeric. Those of Ga
& Tl tend to be liquids or low mp.
H3C
Tl
gas phase
crystalline phase
Indium compound has similar structure
dIn-ring = 285 & 309 pm; pIn3 128E
E; pring 177E
E
3
CH3
In
H3C
H3C
+
H3C
+
Ga CH
CH3
H3C
H3C
CH3
CH3
H3C
+
O
Ga
Br
Br
Ga
Br
Br
O
Me Al O
Me
O
O
5