Li₄Ln[PS₄]₂Cl: Chloride-Containing Lithium Thiophosphates with Lanthanoid Participation (Ln = Pr, Nd and Sm)

The synthesis and structural analysis of three new chloride-containing lithium thiophosphates(V) Li(4)Ln[PS4](2)Cl with trivalent lanthanoids (Ln = Pr, Nd and Sm) are presented and discussed. Single crystals of Li4Sm[PS4](2)Cl were obtained and used for crystal structure determination by applying X-ray diffraction. The other compounds were found to crystallize isotypically in the monoclinic space group C2/c. Thus, Li4Sm[PS4](2)Cl (a = 2089.31(12) pm, b = 1579.69(9) pm, c = 1309.04(8) pm, beta = 109.978(3)degrees, Z = 12) was used as a representative model to further describe the crystal structure in detail since Li4Pr[PS4](2)Cl and Li4Nd[PS4](2)Cl were confirmed to be isotypic using powder X-ray diffraction measurements (PXRD). In all cases, a trigonal structure in the space group R3 (e.g., a = 1579.67(9) pm, c = 2818.36(16) pm, c/a = 1.784, Z = 18, for Li4Sm[PS4](2)Cl) displaying almost identical building units worked initially misleadingly. The structure refinement of Li4Sm[PS4](2)Cl revealed bicapped trigonal prisms of sulfur atoms coordinating the two crystallographically distinct (Sm1)(3+) and (Sm2)(3+) cations, which are further coordinated by four anionic [PS4](3-) tetrahedra. The compounds also contain chloride anions residing within channel-like pores made of [PS4](3-) units. Eight different sites for Li+ cations were identified with various coordination environments (C.N. = 4-6) with respect to chlorine and sulfur. EDXS measurements supported the stoichiometric formula of Li(4)Ln[PS4](2)Cl, and diffuse reflectance spectroscopy revealed optical band gaps of 2.69 eV, 3.52 eV, and 3.49 eV for Li4Sm[PS4](2)Cl, Li4Nd[PS4](2)Cl, and Li4Pr[PS4](2)Cl, respectively. The activation energy for Li+-cation mobility in Li4Sm[PS4](2)Cl was calculated as E-a(Li+) = 0.88 eV using BVEL, which indicates potential as a Li+-cation conductor.