Li9Yb2[PS4]5 and Li6Yb3[PS4]5: two lithium-containing ytterbium(III) thiophosphates(V) revisited

Abstract The lithium ytterbium ortho -thiophosphates Li 9 Yb 2 [PS 4 ] 5 and Li 6 Yb 3 [PS 4 ] 5 were prepared through the reaction of stoichiometric amounts of ytterbium metal, elemental sulfur, red phosphorus and lithium hemisulfide at elevated temperatures in sealed silica tubes. The compounds occur as dark red single crystals which crystallize monoclinically in space group C 2/ c with the lattice parameters a = 1487.98(9), b = 978.63(6), c = 2046.75(12) pm and β = 96.142(3)° for Li 9 Yb 2 [PS 4 ] 5 ( Z = 4) and a = 2814.83(16), b = 997.34(6), c = 3338.52(19) pm and β = 113.685(3)° for Li 6 Yb 3 [PS 4 ] 5 ( Z = 12). Li 9 Yb 2 [PS 4 ] 5 can be assigned to the structure type of Li 9 Nd 2 [PS 4 ] 5 , whereas the structure of Li 6 Yb 3 [PS 4 ] 5 the structure is similar to that of the prototypic Li 6 Gd 3 [PS 4 ] 5 . Both structures feature discrete [PS 4 ] 3– tetrahedra ( d (P–S) = 202–207 pm) and strands of [YbS 8 ] 13− polyhedra ( d (Yb–S) = 271–319 pm) propagating along [010]. When attributed to the general formula (Li 3 [PS 4 ]) x (Yb[PS 4 ]) y , ideas of the dimensionality of both structures can be derived. Whilst the lithium-richer Li 9 Yb 2 [PS 4 ] 5 ( x/y = 1.5) develops planes with the composition ∞ 2 { [ Y b [ P S 4 ] 3 ] 6 − } ${}_{\infty }^{2}\left\{{\left[\mathrm{Y}\mathrm{b}{\left[\mathrm{P}{\mathrm{S}}_{4}\right]}_{3}\right]}^{6-}\right\}$ , Li 6 Yb 3 [PS 4 ] 5 ( x / y = 0.667) exhibits a rather complex three-dimensional network of ytterbium-centered polyhedra connected via [PS 4 ] 3– tetrahedra with lithium cations in the framework structure ∞ 3 { [ Y b 3 [ P S 4 ] 5 ] 6 − } ${}_{\infty }^{3}\left\{{\left[\mathrm{Y}{\mathrm{b}}_{\mathrm{3}}{\left[\mathrm{P}{\mathrm{S}}_{4}\right]}_{5}\right]}^{6-}\right\}$ . These Li + cations are hard to locate in both compounds, but reside in four- to sixfold sulfur coordination ( d (Li–S) = 235–304 pm). Some Li + positions are underoccupied and some Li + cations share sites with Yb 3+ cations in Li 6 Yb 3 [PS 4 ] 5 , and even in Li 9 Yb 2 [PS 4 ] 5 their high displacement values suggest Li + cation mobility. According to the empirical formulae, three Li + cations have to be replaced with one Yb 3+ cation to reach the lithium-poorer compound and structure (Li 6 Yb 3 [PS 4 ] 5 ) starting from the lithium-richer one (Li 9 Yb 2 [PS 4 ] 5 ).