Abstract
Na8Pb2(Ge2S6)2, Na8Sn2(Ge2S6)2, and Na8Pb2(Si2Se6)2 were synthesized by reacting Pb or Sn, Ge, and Na2Sx or Na2Sex flux at 850 °C, 750 °C, and 850 °C respectively. Yellow-orange Na8Pb2(Ge2S6)2 crystallizes in the monoclinic space group C2/m (No. 12) with a=6.839(2) Å, b=11.783(2) Å, c=7.744(2) Å, β= 107.00(2) deg, and V=596.7(4) Å3, Z=1. Dcale = 3.543 g cm-3, number of unique data with F2o>3 σ(F2o), 645, number of variables, 37. The final R/Rw=2.9/3.9. Isostructural ruby-red Na8Sn2(Ge2S6)2 crystallizes in the monoclinic space group C2/m (No. 12) with a=6.849(1) Å, b= 11.777(1) Å, c=7.705(1) Å, β=106.44(1) deg, and V=596.1(3) Å3, Z=1. Dcale= 3.054 g cm-3, number of unique data with F2o>3 σ(F2o), 480, number of variables, 38. The final R/Rw = 2.1/2.7. Isostructural red-orange Na8Pb2(Si2Se6)2 crystallizes in the monoclinic space group C2/m (No. 12) with a=7.070(3) Å, b= 12.214(3) Å, c=7.969(3) Å, β=107.29(3) deg, and V=657.1(4) Å3, Z 1. Dcale=4.190 g cm-3, number of unique data with F2o3 >3 σ(F2o), 494, number of variables, 37. The final R/Rw = 2.4/3.4. The structure of these new materials consists of [Ge2S6]6- or [Si2Se6]6- ethane-like fragments surrounded by metal cationic sites which are occupied either by sodium or by mixtures of sodium and lead or tin. The ordering of Pb on these cationic sites leads to a 2-dimensional "layered" morphology for Na8Pb2(Ge2S6)2 while the ordering of Sn on the cationic sites leads to a 3-dimensional "chunky" morphology for Na8Sn2(Ge2S6)2. The ordering of Pb on the cationic sites in Na8Pb2(Si2Se6)2, is the same as the ordering in Na8Pb2(Ge2S6)2 although the crystal morphology is chunky rather than layered. Raman and vibrational spectroscopic data are consistent with the presence of [Ge2S6]6- fragments in the first two compounds. Single crystal optical spectra indicate that these semiconductors have bandgaps of 2.43 eV for Na8Pb2(Ge2S6)2 and 2.06 eV for Na8Sn2(Ge2S6)2.
Original language | English |
---|---|
Pages (from-to) | 122-128 |
Number of pages | 7 |
Journal | Journal of Alloys and Compounds |
Volume | 259 |
Issue number | 1-2 |
DOIs | |
Publication status | Published - Aug 22 1997 |
Keywords
- Ligand binding
- [GeS] ligands
- [SiSe] ligands
ASJC Scopus subject areas
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry