| Summary: | The synthesis and structural analysis of three new chloride-containing lithium thiophosphates(V) Li<sub>4</sub><i>Ln</i>[PS<sub>4</sub>]<sub>2</sub>Cl with trivalent lanthanoids (<i>Ln</i> = Pr, Nd and Sm) are presented and discussed. Single crystals of Li<sub>4</sub>Sm[PS<sub>4</sub>]<sub>2</sub>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 <i>C</i>2/<i>c</i>. Thus, Li<sub>4</sub>Sm[PS<sub>4</sub>]<sub>2</sub>Cl (<i>a</i> = 2089.31(12) pm, <i>b</i> = 1579.69(9) pm, <i>c</i> = 1309.04(8) pm, <i>β</i> = 109.978(3)°, <i>Z</i> = 12) was used as a representative model to further describe the crystal structure in detail since Li<sub>4</sub>Pr[PS<sub>4</sub>]<sub>2</sub>Cl and Li<sub>4</sub>Nd[PS<sub>4</sub>]<sub>2</sub>Cl were confirmed to be isotypic using powder X-ray diffraction measurements (PXRD). In all cases, a trigonal structure in the space group <i>R</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover><mn>3</mn><mo>¯</mo></mover></mrow></semantics></math></inline-formula> (e.g., <i>a</i> = 1579.67(9) pm, <i>c</i> = 2818.36(16) pm, <i>c/a</i> = 1.784, <i>Z</i> = 18, for Li<sub>4</sub>Sm[PS<sub>4</sub>]<sub>2</sub>Cl) displaying almost identical building units worked initially misleadingly. The structure refinement of Li<sub>4</sub>Sm[PS<sub>4</sub>]<sub>2</sub>Cl revealed bicapped trigonal prisms of sulfur atoms coordinating the two crystallographically distinct (Sm1)<sup>3+</sup> and (Sm2)<sup>3+</sup> cations, which are further coordinated by four anionic [PS<sub>4</sub>]<sup>3−</sup> tetrahedra. The compounds also contain chloride anions residing within channel-like pores made of [PS<sub>4</sub>]<sup>3−</sup> units. Eight different sites for Li<sup>+</sup> cations were identified with various coordination environments (<i>C.N.</i> = 4–6) with respect to chlorine and sulfur. EDXS measurements supported the stoichiometric formula of Li<sub>4</sub><i>Ln</i>[PS<sub>4</sub>]<sub>2</sub>Cl, and diffuse reflectance spectroscopy revealed optical band gaps of 2.69 eV, 3.52 eV, and 3.49 eV for Li<sub>4</sub>Sm[PS<sub>4</sub>]<sub>2</sub>Cl, Li<sub>4</sub>Nd[PS<sub>4</sub>]<sub>2</sub>Cl, and Li<sub>4</sub>Pr[PS<sub>4</sub>]<sub>2</sub>Cl, respectively. The activation energy for Li<sup>+</sup>-cation mobility in Li<sub>4</sub>Sm[PS<sub>4</sub>]<sub>2</sub>Cl was calculated as <i>E</i><sub>a</sub>(Li<sup>+</sup>) = 0.88 eV using BVEL, which indicates potential as a Li<sup>+</sup>-cation conductor.
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