LITHIUM CATIONS TIGHTLY BOUND TO POLYCHALCOGENIDES - SYNTHESIS AND SOLID-STATE STRUCTURES OF LI2S6(TEEDA)2, LI2S4(PMDETA)2, AND LI2SE5(PMDETA)2

Addition of N,N,N',N'-tetraethylethylenediamine (teeda) and N,N,N',N'' ,N'''-pentamethyldicthylenetriamine (pmdeta) to a toluene suspension o f Li2S2 resulted in a homogeneous orange-red solution, from which we i solated Li2S6(teeda)2 (2) and Li2S4(pmdeta)2 (3), respectively. The se lenide analog of 3, Li2Se5(pmdeta)2 (4), has been obtained from a redd ish-brown toluene solution containing Li2Se2 and pmdeta, while a simil ar treatment of Li2Se2 and N,N,N,N'-tetramethylethylenediamine (tmeda) yielded Li2Se4(tmeda)2 (5). In contrast, the Li2Se2/teeda system depo sited lithium metal as particles or as a mirror. The lithium chalcogen ides 2-4 have been characterized by X-ray structure determinations. Cr ystal data: 2, monoclinic space group P2(1), a = 9.862(4) angstrom, b = 17.337(7) angstrom, c = 10.243(6) angstrom, beta = 115.83(4)-degrees , Z = 2, R = 0.057, and R(w) = 0.083 for 2928 independent reflections; 3, monoclinic space group P2(1)/c, a = 14.04(l) angstrom, b = 14.23(1 ) angstrom, c = 16.007(7) angstrom, beta = 11 1.08(5)-degrees, Z = 4, R = 0.054, and R(w) = 0.058 for 2171 independent reflections with I > 3.0sigma(I); 4, triclinic space group P1BAR, a = 9.808(7) angstrom, b = 18.227(3) angstrom, c = 8.7930(6) angstrom, alpha = 98.092(9)-degree s, beta = 90.13(2)-degrees, gamma = 90.72(4)-degrees, Z = 2, R = 0.044 , and R(w) = 0.055 for 3634 independent reflections with I > 3.0sigma( I). These crystals all consist of discrete molecular units, in which l ithium ions are tightly bound to terminal chalcogen atoms. No strong i ntermolecular interactions were noticed. Molecule 2 has an intriguing bicyclic Li2S6 geometry, while the S4(2-) unit in 3 and the Se5(2-) un it in 4 exhibit zigzag chain structures. The Raman spectra of 2 and 3 and the H-1 NMR spectra of 2-4 are discussed.