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Ch 14. Group 14. Elemental forms. Diamond structured metals. E g /eV R/ cm C 5.5 insulator 10 15 Si 1.1 semicon 50 Ge 0.6 semicon 30 Sn small metallic 10 −5. +. Discovery of fullerenes. www.chemistry.oregonstate.edu/courses/ch412/gobeavs/bucky.ppt.

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Diamond structured metals
Diamond structured metals

Eg /eV R/ cm

C 5.5 insulator 1015

Si 1.1 semicon 50

Ge 0.6 semicon 30

Sn small metallic 10−5


Discovery of fullerenes

+

Discovery of fullerenes

www.chemistry.oregonstate.edu/courses/ch412/gobeavs/bucky.ppt

From “Designing the Molecular World” by Phillip Ball, Princeton, 1994


Icosahedral symmetry
Icosahedral symmetry

C60 indicating reactive p-orbitals


Fullerenes
Fullerenes

C60 soln

C70 soln

FCC solid structure


C 60 reduction
C60 reduction

Cyclic

voltammetry


Fullerene derivatives
Fullerene derivatives

[Pt(PPh3)2(C60)]

(h2C70fullerene)carbonylchlorobis(triphenylphosphine)iridium

Balch, Catalano, Lee, Olmstead, Parkin, JACS 113, 8953,1991.


Carbon nanotubes
Carbon Nanotubes

Multi-walled nanotube (MWNT)

End-closed

Sm2O3 in nanotube




Halides
Halides

CF4 not a LA

SiF4

GeF4

SnF4

PbF4

ex SiF4 + 2HF  H2SiF6

Note: PbF4 is a strong oxidant due to inert pair effect

All readily hydrolyze in air - except CF4


Pbf 4 and pbo

PbO

PbF4 and PbO


Carbides
Carbides

CaC2


Polyanion clusters
Polyanion clusters

Zintl ions

Pb52

using Wades’ rules for ecounting

# epairs = ½ (5 (2) + 2) = 6 which is (n+1) or closo

Sn94

# epairs = ½ (9 (2) + 4) = 11 which is (n+2) nido

These are strong reducing agents, prepared in NH3 (anhyd, liq) or H2NCH2CH2NH2 (anhyd, liq)


Graphite structure
Graphite structure

  • C-C in-plane = 1.42 Å

  • Usually (AB)n hexgonal stacking

  • Interlayer distance

    = 3.354 Å

Graphite is a semi-metal, chemically stable, light, strong

A

B

Source: http://www.ccs.uky.edu/~ernst/

A


Graphite intercalation
Graphite Intercalation

Cx → Cx+ + e− E ~ −1.3 V

(so no Cx+An− compounds in aqu solution)

Cx + BF3 + ½F2 CxBF4

Cx +AlCl3+ 1/2Cl2 CxAlCl4

Domain structure


Some acceptor type gic s
Some acceptor-type GIC’s

Blue: obs

Pink: calc

CxSO3C8F17

CxB(O2C2(CF3)4)2


Graphite lithiation
Graphite Lithiation

Expands about

10% along z

Graphite lithiation: approx 0.2-0.3 V vs Li+/Li

Theoretical capacity:

Li metal > 1000 mAh/g

C6Li 370

Actual C6Li formation: 320 – 340 mAh/g reversible;

20 – 40 irreversible


Lithium ion batteries
Lithium ion batteries

Cathode

LiCoO2 Li1-xCoO2 + xLi+ + xe-

Anode

6C + Li+ + e- C6Li

Electrolyte

Organic solvent with LiPF6


Orthosilicates
Orthosilicates

Basic unit is SiO4 (Td) Si4+, O2−

MgxMnyFe2-x-ySiO4 (peridot)

Ortho = isolated SiO44− ions

green color from Fe(II)

hcp O array, Si in 1/8 Td sites

and Mg,Fe,Mn in 1/2 Oh sites


Single chain metasilicates
Single chain metasilicates

NaAl(SiO3)2

Jadeite

(SiO32−)n

shared O has no charge

apical O has 1− charge



Beryl structure
Beryl structure

Si6O1812− = (SiO32−)6 ring

Be3Al2Si6O18 is beryl

Be3Al2−xCrxSi6O18 is emerald


Sheet silicates
Sheet silicates

mica

2:1 clay minerals




3d frameworks

SiO2

3D frameworks

-quartz varieties include amethyst, agate.

Also tridymite, cristobalite

All corner sharing Td

MP ~1700 C

Due to slow rearrangement to crystallize, these readily form amorphous glass (vitreous silica)

Borosilicates – add Na2O, B2O3 as network modifiers (Pyrex)


3d frameworks aluminosilicates
3D frameworks - aluminosilicates

Sodalite cages = (Al3Si)24O48

Zeolite A

corner sharing Td with Al substitution for Si, which gives negative charge on framework

Nax[(AlO2)x(SiO2)] · δ H2O x < 1 (no Al-O-Al links)


Zeolite frameworks

Na2SiO3 (hyd) + NaAlO2 (hyd) → NaAlSiO4(hyd)

N(OEt)3

Zeolite frameworks


Siloxanes
Siloxanes

Si + 2CH3Cl  (CH3)2SiCl2

Controlled hydrolysis to [(CH3)SiO]n + 2 HCl

Si3O3(CH3)6 [(CH3)2SiO]n polydimethylsiloxane (silicone)

Some additives (CH3)3SiCl chain termination

CH3SiCl3 crosslinker

(CH3)(C6H5)SiCl2 phenyl groups increase

crystallinity and modulus


Siloxanes1
Siloxanes

8 CH3SiCl3 + 12 H2O → cyclo-(CH3)8Si8O12 + 24 HCl

Cubic arrangement


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