Flux-assisted polytypism in the [Na₂Cl]GaQ₂ heterolayered salt-inclusion chalcogenide family

Abstract

Two polytypic heterolayered salt-inclusion chalcogenides, o-[Na2Cl]GaQ2 and t-[Na2Cl]GaQ2, were obtained via a NaCl/NaI flux-assisted synthesis, as part of an investigation of the Na–Ga–Q (Q = S and Se) system. The...

Advances in Chalcogenide Crystal Growth: Flux and Solution Syntheses, and Approaches for Postsynthetic Modifications

“…Even finding the appropriate conditions for reaction workup, i.e., flux dissolution, can be tricky since the crystal product should not itself react with or be soluble in the solvent used for the flux dissolution. − The flux not only assists in crystal growth but also offers control over the reaction products. For example, the flux, often a salt, can integrate into the structure and form salt-inclusion materials or mixed-anion compositions. , When the flux is not reactive with the reagents, it can still affect the final phase. For instance, different flux compositions, NaCl, NaCl/NaI, and NaBr/NaI, in the Na–Ga–Se system can facilitate the crystallization of NaGa 3 Se 5 , [Na 2 Cl]­GaSe 2 , Na 2 GaSe 3 , and Na 4 Ga 2 Se 5 phases, respectively. , Moreover, the flux can mediate the formation of specific polymorphs, as is demonstrated in the crystallization of orthorhombic-[Na 2 Cl]­GaS 2 (Na 2 S n /NaCl flux) versus tetragonal-[Na 2 Cl]­GaS 2 (Na 2 S n /NaCl/NaI flux) , and monoclinic (no flux) versus cubic (KI flux) polymorphs of Ga 2 S 3 …”

“…(left) Schematic classification of salt-inclusion materials by covalent and ionic framework dimensionality. (right) Examples of hybrid materials with 0D-0D, [Cs 6 Cl] 2 Cs 5 Ga 15 Ge 9 Se 48 , 2D-2D, [Na 2 Cl]­Ga Q 2 , 2D-0D, [Cs 6 X ] A Ga 6 Q 12 , frameworks and salt-inclusion fragment dimensionalities, respectively. Gray and green shapes represent covalent and ionic moieties, respectively.…”

“…The driving force of the water intercalation process is a combination of the layered nature of the pristine material and the energetically beneficial hydration of the Na + ions (significant negative hydration enthalpy) . Notably, the [Na 2 Cl]­GaS 2 SIC material, consisting of similar GaS 2 – layers and [Na 2 Cl] + salt inserts, does not undergo hydration, implying that the chalcogenide coordination environment of Na + is also a prerequisite for water intercalation. , Another intriguing example of water intercalation in layered chalcogenides is water uptake in NaCuU Q 3 ( Q = S and Se, space group Cmcm ) and formation of NaCuU Q 3 · x H 2 O ( x ≈ 1.5, space group P 2/ m ) . Similar to the NaGaS 2 · x H 2 O structure, only CuU Q 3 – layers were resolved by SC-XRD, and the formula determination required DFT calculations, TGA, and IR spectroscopy.…”

“…Similar to what was observed for [Cs 6 Cl] 2 Cs 5 Ga 15 Ge 9 Se 48 , the exchange took place only on the salt-inclusion part of the structure and did not involve the A + ions. Attempts to perform ion exchange on the 2D-2D [Na 2 Cl]­Ga Q 2 ( Q = S and Se) compounds did not succeed and led to structure decomposition . Thus, there is a possible limitation to SCSC ion-exchange modification for SIC materials: more complex dimensionalities of the salt-inclusion substructure (>0D) may participate in the exchange too vigorously, resulting in structural degradation.…”