Synthesis and reversible hydration behavior of the thiosulfate intercalated layered double hydroxide of Zn and Al S. Radha a , Wolfgang Milius b , Josef Breu b , P. Vishnu Kamath a,n a Department of Chemistry, Central College, Bangalore University, Bangalore-560 001, India b Department of Inorganic Chemistry I, University of Bayreuth, Bayreuth, Germany article info Article history: Received 23 March 2013 Received in revised form 5 June 2013 Accepted 9 June 2013 Available online 18 June 2013 Keywords: Layered double hydroxides Thiosulfate ion Hydration–dehydration Interstratification abstract The thiosulfate-intercalated layered double hydroxide of Zn and Al undergoes reversible hydration with a variation in the relative humidity of the ambient. The hydrated and dehydrated phases, which represent the end members of the hydration cycle, both adopt the structure of the 3R 1 polytype. In the intermediate range of relative humidity values (40–60%), the hydrated and dehydrated phases coexist. The end members of the hydration cycle adopt the structure of the same polytype, and vary only in their basal spacings. This points to the possibility that all the intermediate phases have a kinetic origin. & 2013 Elsevier Inc. All rights reserved. 1. Introduction The layered double hydroxide (LDH) of Zn and Al comprises a stacking of positively charged layers of the composition [Zn 2 Al (OH) 6 ] + , with anions intercalated in the interlayer region. A wide variety of anions like monoatomic halides, simple inorganic anions like CO 3 2- , SO 4 2- , NO 3 - , IO 3 - and organic anions like sulfonates, phosphonates, and carboxylates can be lodged in the interlayer [1]. By virtue of their interlayer chemistry they find extensive applica- tions as anion exchangers, adsorbents, catalysts, sensors, drug delivery agents, and fire retardants [2–4]. The structure of the LDH is modeled on that of the mineral brucite, Mg(OH) 2 . Mg(OH) 2 comprises a hexagonal close packing of hydroxyl ions in which alternative layers of octahedral sites are occupied by Mg 2+ ions. This arrangement of atoms leads to a stacking of charge-neutral metal hydroxide layers having the composition [M II (OH) 2 ]. When a fraction, x, of the divalent metal is substituted with a trivalent metal such as Al 3+ , the layers acquire a positive charge with a composition [M II 1-x Al x (OH) 2 ] x+ . Anions along with the water molecules enter the interlayer for charge compensation. Thiosulfate (S 2 O 3 2- ) is one of the simple inorganic anions with C 3v symmetry. Thiosulfate is interesting as it has S in two different oxidation states and is a well-known redox reagent [5]. It forms soluble metal complexes [6] and is used for dechlorination of water [7]. Owing to these properties, thio- sulfate finds applications in several fields as a titration stan- dard [8], as an agent in rapid dechlorination of water [9], antidote to cyanide poisoning [10], metal cleaning agent [11], antirheumatic [12], in silver halide photography [13], and in fabric and paper bleaching [8]. Despite its importance, there are only a few reports of thiosulfate intercalation into the LDH gallery. Thomas et al. [14, 15] report the synthesis of thiosulfate-LDH by anion exchange and study the intracrystal- line oxidation of thiosulfate in the interlayer using H 2 O 2 and I 2 to derive sulfate-LDHs devoid of carbonate contamination. Different conditions yield different polytypes of the sulfate LDH. Khan et al. [16] report the release kinetics of intercalated thiosulfate ions from [Mg–Al] and [Li–Al] LDHs into water and dodecylsulfate solution for its possible applications in textile industries. However, the authors in both the cases have not focussed on the structure and hydration behavior of the thiosulfate-LDH. Thiosulfate is an oxo-anion whose structure is similar to sulfate with one of its O atoms replaced by S. Sulfate LDHs are known to exhibit a wide variety of polytypic structures [17]. They also exhibit interesting basal spacing dynamics owing to hydration– dehydration of the interlayer [18]. Given the interesting properties of the thiosulfate ion and its close structural relationship with the sulfate ion, in this paper, we investigate the synthesis of thiosul- fate intercalated LDHs and study their hydration behavior. We focus on polytypism among S 2 O 3 2- -LDHs and the relative humidity induced basal spacing dynamics and possible interpolytype transformations. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jssc Journal of Solid State Chemistry 0022-4596/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2013.06.010 n Corresponding author. E-mail addresses: josef.breu@uni-bayreuth.de (J. Breu), vishnukamath8@hotmail.com (P.V. Kamath). Journal of Solid State Chemistry 204 (2013) 362–366