Two Hitherto Unknown Lithium Holmium(III) Ortho‐Thiophosphates(V): Li₉Ho₂[PS₄]₅ and Li₁₅Ho₇[PS₄]₁₂

Abstract

Dedicated to Professor Josef Breu on the Occasion of his 60 th Birthday. The two hitherto unknown lithium holmium(III) ortho-thiophosphates(V) Li 9 Ho 2 [PS 4 ] 5 and Li 15 Ho 7 [PS 4 ] 12 crystallize in the monoclinic space group C2/c with the lattice parameters a = 1489.43(9) pm, b = 979.84(6) pm, c = 2051.68(12) pm, β = 96.221(3)°for Li 9 Ho 2 [PS 4 ] 5 (Z = 4) and a = 2826.73(16) pm, b = 1003.25(6) pm, c = 3361.46(19) pm, β = 113.992(3)°for Li 15 Ho 7 [PS 4 ] 12 (Z = 5). While Li 9 Ho 2 [PS 4 ] 5 extends the Li 9 RE 2 [PS 4 ] 5 series, Li 15 Ho 7 [PS 4 ] 12 can be regarded as a cation-distribution variant of the Li 6 RE 3 [PS 4 ] 5 series (Z = 12). Both structures feature characteristic [HoS 8 ] 13À polyhedra (d(Ho 3 + À S 2À ) = 275-314 pm) and [PS 4 ] 3Àtetrahedra (d(P 5 + À S 2À ) = 202-207 pm), but Li 15 Ho 7 [PS 4 ] 12 exhibits one Ho 3 + position, which is mixed occupied with Li + and settles with C.N. = 6 + 2. The coordination numbers of all other Li + cations range from four to six in both new compounds with Li + À S 2À distances from 238 to 317 pm.

Structure and Ionic Conductivity of Li-Disordered Bismuth o-Thiophosphate Li60–3xBi16+x(PS4)36

“…The restricted dimensionality of the diffusion pathways and their narrow/bottleneck-like nature are the reasons for the overall low ionic conductivities. For the related lanthanide compounds Li 9 Ho 2 (PS 4 ) 5 and Li 15 Ho 7 (PS 4 ) 12 , one-dimensional pathways with energy barriers of 0.378 and 0.727 eV, respectively, and three-dimensional pathways with energy barriers of 0.471 and 0.838 eV, respectively, have been reported. Notably, in LiBiPS, the Bi3/Li3 sites are also part of the lithium ion percolation pathways (see the right side of Figure a) in the high-density region (blue box in Figure b) and a variation of the bismuth content thus alters the diffusion pathways along these sites.…”

“…LiBiPS shows a structural relationship to lithium rare earth metal thiophosphates such as Li 6 Ln 3 (PS 4 ) 5 with Ln = Gd, Dy, Y, Yb, or Lu 45 , 46 and Li 9 Ln 2 (PS 4 ) 5 with Ln = Nd, 47 Ho, 48 or Yb. 46 Indeed, the title compound shows similar coordination environments for lithium, phosphorus, and the trivalent metal compared to Li 6 Ln 3 (PS 4 ) 5 and Li 9 Ln 2 (PS 4 ) 5 , but due to the increased size of the bismuth cation as well as its stereochemically active lone pair, the arrangement slightly differs and can be seen as a structural fusion of the two different structure types of Li 6 Ln 3 (PS 4 ) 5 and Li 9 Ln 2 (PS 4 ) 5 .…”

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

“…This appears to be quite high, though reasonable, keeping in mind that the lithium cations are mostly bound to the chloride anions sitting in what can be described as tunnels in the structure. In other lithium-containing rare-earth metal thiophosphates(V), for example, Li 3 La[PS 4 ] 2 (1D-E a (Li + ) = 0.44 eV) [20] or Li 9 Ho 2 [PS 4 ] 5 (1D-E a (Li + ) = 0.38 eV) [19], the energy barrier is lower than the chloride-containing one, as expected, due to only one sort of anion being present. The bond-valence energy landscapes give a direction on what could be the diffusion behavior of the ions, but experimental data are crucial.…”

“…On the other hand, when only sodium is used as a monovalent cation, exclusively thiophosphate(IV) groups [P 2 S 6 ] 4− are present as complex counter ions [13,15,16]. This seems to be a special case for sodium, as the lightest alkali metal lithium yields compounds with compositions like Li 9 RE 2 [PS 4 ] 5 (x = 3, y = 2) [17,18], Li 6 RE 3 [PS 4 ] 5 (x = 2, y = 3) [2,18] or Li 15 RE 7 [PS 4 ] 12 (x = 5, y = 7) [19] , where again only ortho-thiophosphate(V) anions [PS 4 ] 3− are present. Recently, the first thiophosphate with the lightest lanthanoid, namely Li 3 La[PS 4 ] 2 (x = y = 1) [20], has been published.…”

“…When lanthanum is used as a rare-earth metal, this leads to the formation of orthorhombic Li 3 La[PS 4 ] 2 [20]. On the other hand, when Ln = Nd and Sm-Lu are employed, the resulting lithium compounds, either with the phase compositions Li 9 Ln 2 [PS 4 ] 5 , Li 6 Ln 3 [PS 4 ] 2 [2,18] or Li 15 Ln 7 [PS 4 ] 12 [19] crystallize in a monoclinic lattice. However, while examining the lighter lanthanoid systems, including chlorine, such as for Ln = Pr, Nd and Sm, crystal formation with an intriguing phenomenon of twinning arises.…”