Ch 14. Group 14

2 Elemental forms

3 Diamond structured metals E g /eVR/ cm C5.5insulator10 15 Si1.1semicon50 Ge0.6semicon30 Snsmallmetallic10 −5

4 Discovery of fullerenes + From “Designing the Molecular World” by Phillip Ball, Princeton,

5 Icosahedral symmetry C 60 indicating reactive p- orbitals

6 Fullerenes C 60 soln C 70 soln FCC solid structure

7 C 60 reduction Cyclic voltammetry

8 Fullerene derivatives (  2 C 70 fullerene)carbonylchlorobis(triphen ylphosphine)iridium Balch, Catalano, Lee, Olmstead, Parkin, JACS 113, 8953,1991. [Pt(PPh 3 ) 2 (C 60 )]

9 Carbon Nanotubes Multi-walled nanotube (MWNT) End-closed Sm 2 O 3 in nanotube

10 Bond enthalpies

11 Heavier congeners

12 Halides CF 4 not a LA SiF 4 GeF 4 SnF 4 PbF 4 ex SiF 4 + 2HF  H 2 SiF 6 Note: PbF 4 is a strong oxidant due to inert pair effect All readily hydrolyze in air - except CF 4

13 PbF 4 and PbO PbO

14 Carbides CaC 2

15 Polyanion clusters Pb 5 2  using Wades’ rules for e  counting # e  pairs = ½ (5 (2) + 2) = 6 which is (n+1) or closo Sn 9 4  # e  pairs = ½ (9 (2) + 4) = 11 which is (n+2) nido These are strong reducing agents, prepared in NH 3 (anhyd, liq) or H 2 NCH 2 CH 2 NH 2 (anhyd, liq) Zintl ions

16 Graphite structure C-C in-plane = 1.42 Å Usually (AB) n hexgonal stacking Interlayer distance = Å Source: A B A Graphite is a semi-metal, chemically stable, light, strong

17 Graphite Intercalation C x → C x + + e − E ~ −1.3 V (so no C x + An − compounds in aqu solution) C x + BF 3 + ½ F 2  C x BF 4 C x + AlCl / 2 Cl 2  C x AlCl 4 Domain structure

18 C x B(O 2 C 2 (CF 3 ) 4 ) 2 Some acceptor-type GIC’s Blue: obs Pink: calc C x SO 3 C 8 F 17

19 Graphite Lithiation Graphite lithiation:approx V vs Li + /Li Theoretical capacity: Li metal> 1000 mAh/g C 6 Li 370 Actual C 6 Li formation: 320 – 340 mAh/g reversible; 20 – 40 irreversible Expands about 10% along z

20 Lithium ion batteries Cathode LiCoO 2  Li 1-x CoO 2 + xLi + + xe - Anode 6C + Li + + e -  C 6 Li Electrolyte Organic solvent with LiPF 6

21 Orthosilicates Mg x Mn y Fe 2-x-y SiO 4 (peridot) Basic unit is SiO 4 (Td) Si 4+, O 2− hcp O array, Si in 1 / 8 Td sites and Mg,Fe,Mn in 1/2 Oh sites green color from Fe(II) Ortho = isolated SiO 4 4− ions

22 Single chain metasilicates NaAl(SiO 3 ) 2 Jadeite (SiO 3 2− ) n shared O has no charge apical O has 1− charge

23 Double chain metasilicates

24 Beryl structure Si 6 O 18 12− = (SiO 3 2− ) 6 ring Be 3 Al 2 Si 6 O 18 is beryl Be 3 Al 2−x Cr x Si 6 O 18 is emerald

25 Sheet silicates mica2:1 clay minerals

26 Clays

27 Clay minerals

28 3D frameworks SiO 2  -quartz varieties include amethyst, agate. Also tridymite, cristobalite All corner sharing T d MP ~1700  C Due to slow rearrangement to crystallize, these readily form amorphous glass (vitreous silica) Borosilicates – add Na 2 O, B 2 O 3 as network modifiers (Pyrex)

29 3D frameworks - aluminosilicates Zeolite A corner sharing Td with Al substitution for Si, which gives negative charge on framework Na x [(AlO 2 ) x (SiO 2 )] · δ H 2 O x < 1 (no Al-O-Al links) Sodalite cages = (Al 3 Si) 24 O 48

30 Zeolite frameworks Na 2 SiO 3 (hyd) + NaAlO 2 (hyd) → NaAlSiO 4 (hyd)  N(OEt) 3

31 Siloxanes Si + 2CH 3 Cl  (CH 3 ) 2 SiCl 2 Controlled hydrolysis to [(CH 3 )SiO] n + 2 HCl Si 3 O 3 (CH 3 ) 6 [(CH 3 ) 2 SiO] n polydimethylsiloxane (silicone) Some additives (CH 3 ) 3 SiCl chain termination CH 3 SiCl 3 crosslinker (CH 3 )(C 6 H 5 )SiCl 2 phenyl groups increase crystallinity and modulus

32 Siloxanes 8 CH 3 SiCl H 2 O → cyclo-(CH 3 ) 8 Si 8 O HCl Cubic arrangement