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Ch 14. Group 14

Ch 14. Group 14

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Ch 14. Group 14

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  1. Ch 14. Group 14

  2. Elemental forms

  3. 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

  4. + Discovery of fullerenes www.chemistry.oregonstate.edu/courses/ch412/gobeavs/bucky.ppt From “Designing the Molecular World” by Phillip Ball, Princeton, 1994

  5. Icosahedral symmetry C60 indicating reactive p-orbitals

  6. Fullerenes C60 soln C70 soln FCC solid structure

  7. C60 reduction Cyclic voltammetry

  8. Fullerene derivatives [Pt(PPh3)2(C60)] (h2C70fullerene)carbonylchlorobis(triphenylphosphine)iridium Balch, Catalano, Lee, Olmstead, Parkin, JACS 113, 8953,1991.

  9. Carbon Nanotubes Multi-walled nanotube (MWNT) End-closed Sm2O3 in nanotube

  10. Bond enthalpies

  11. Heavier congeners

  12. 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

  13. PbO PbF4 and PbO

  14. Carbides CaC2

  15. 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)

  16. 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

  17. 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

  18. Some acceptor-type GIC’s Blue: obs Pink: calc CxSO3C8F17 CxB(O2C2(CF3)4)2

  19. 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

  20. Lithium ion batteries Cathode LiCoO2 Li1-xCoO2 + xLi+ + xe- Anode 6C + Li+ + e- C6Li Electrolyte Organic solvent with LiPF6

  21. 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

  22. Single chain metasilicates NaAl(SiO3)2 Jadeite (SiO32−)n shared O has no charge apical O has 1− charge

  23. Double chain metasilicates

  24. Beryl structure Si6O1812− = (SiO32−)6 ring Be3Al2Si6O18 is beryl Be3Al2−xCrxSi6O18 is emerald

  25. Sheet silicates mica 2:1 clay minerals

  26. Clays

  27. Clay minerals

  28. 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)

  29. 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)

  30. Na2SiO3 (hyd) + NaAlO2 (hyd) → NaAlSiO4(hyd) N(OEt)3 Zeolite frameworks

  31. 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

  32. Siloxanes 8 CH3SiCl3 + 12 H2O → cyclo-(CH3)8Si8O12 + 24 HCl Cubic arrangement