Size-Driven Stability of Lanthanide Thiophosphates Grown from an Iodide Flux

Abstract

To determine the influence of the lanthanide size on the structures and properties of thiophosphates, a thiophosphate series containing different lanthanides was synthesized via high temperature flux crystal growth and their structures and physical properties analyzed and compared. Layered thiohypophosphates NaLnP 2 S 6 (Ln = La, Ce, Pr) and thiopyrophosphates CsLnP 2 S 7 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Y) were grown out of an iodide flux using consistent reaction conditions across both series. Under the mildly reducing iodide flux reaction conditions, a rather rare example of phosphorus reduction from the +5 to the +4 oxidation state was observed. Both resultant structure types are based on lanthanide thiophosphate sheets with the alkali cations located between them. Magnetic susceptibility measurements were conducted and revealed Curie−Weiss behavior of the samples, with a Van Vleck contribution in the CsSmP 2 S 7 sample. UV−vis data was found to be in good agreement with the literature, indicating little influence of the sulfide environment on the localized 4f orbitals.

Synthesis of Hydrated Ternary Lanthanide-Containing Chlorides Exhibiting X-ray Scintillation and Luminescence

“…It is well established that the later lanthanides, due to their smaller sizes, tend to adopt coordination numbers lower than those of the early lanthanides. As an illustration, Klepov et al have reported that in the extended lanthanide series of NaLnP 2 S 6 (Ln = La, Ce, or Pr) and CsLnP 2 F 7 (Ln = Nd–Yb or Y), the early lanthanides take on 9-fold coordination, while the later lanthanide cations favor a coordination number of 8 . These high coordination numbers, combined with the tendency of lanthanides to be quite flexible when it comes to the geometry of their coordination environment, can readily cause uniform reaction conditions to result in different compositions and crystal structures.…”

“Soft” Alkali Bromide and Iodide Fluxes for Crystal Growth

“…The downside of using the binary compounds is the occasional difficulty of obtaining binary phases that are not commercially available or binary starting reagents that contain unexpected impurities that alter the outcome of the reaction, with product formation depending on the reagent's lot (Wells et al, 2010 ). For example, rare earth sulfides are not currently commercially available, except for lanthanum sulfide, and require additional experiments to obtain the pure starting materials (Klepov et al, 2019a ).…”

“…Similarly, KBr and CsBr fluxes at 950°C were used to obtain Rb 3 Ln 3 [PS 4 ] 4 ( Ln = Pr, Er) and Cs 3 Pr 5 [PS 4 ] 6 (Komm and Schleid, 2004 , 2005 ). Crystal growth of rare earth sulfides Na Ln P 2 S 6 ( Ln = La and Ce) and CsLnP 2 S 7 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Y) was facilitated by a CsI/NaI flux at 500°C (Klepov et al, 2019a ). The synthesis of the Na Ln P 2 S 6 compounds is preceded by reduction of the P(V) containing P 2 S 5 starting material to P(IV) in P 2 .…”

Li3La[PS4]2: The First Lithium Lanthanum Ortho‐Thiophosphate

“…= 7-9) from sulfur ligands of the [PS 4 ] 3À anions as well. Further studies on the incorporation of the lighter alkali metals (A = Li and Na) into the lanthanoid(III)-thiophosphate(V) matrix failed in the case of sodium, for the complex anion always becomes [P 2 S 6 ] 4À as hexathiodiphosphate(IV) instead of the ortho-thiophosphate(V), e. g. in NaLa[P 2 S 6 ], [14] NaSm[P 2 S 6 ] [15] and NaTb[P 2 S 6 ]. [16] In 2006 and 2007, the first lithium-containing compounds Li 9 Nd 2 [PS 4 ] 5 [17] and Li 6 Gd 3 [PS 4 ] 5 [18] have been published and meanwhile, besides Li 9 Yb 2 [PS 4 ] 5 [19][20][21] and Li 6 Yb 3 [PS 4 ] 5 , [19][20][21] several other Li 9 Ln 2 [PS 4 ] 5 (Ln = Pr, Sm, Dy, Ho, Er and Lu) [19,20] and Li 6 Ln 3 [PS 4 ] 5 (Ln = Gd, Dy, Ho and Lu) [19,18] phases are known, again with complex [PS 4 ] 3À anions in their crystal structures.…”