Inorganic Synthesis

Sodium thioantimonate(V) synthesis

Theory:

Sodium thioantimonate nonahydrate Na3SbS4.9H2O (also known as Schlippe´s salt) represents one of a few commercially available antimony salts that have found world-wide industrial application. The compound crystallizes in a cubic crystal system and it forms rare bright-yellow tetrahedral crystals. Its structure was first determined in 1950 [1], however, the hydrogen bonds were refined not until 1979 by Meitener [2]. Raman spectroscopy has been also performed on this salt and the vibrational spectra are available on the Internet [3]. However, other any additional data (solubility, thermal characterization, IR spectrum) are missing. Also, up to our knowledge, no photo of the salt has been published. In this article we provide modified synthetic route towards Na3SbS4.9H2O using naturally found antimony mineral – stibnite. The photos of the product are given too.

Procedure:

For the synthesis, modified procedure of PREPCHEM was used. Bulk antimony(III) sulfide (10 g, 0.029 mol) from natural source (Dubrava antimony deposit, Slovakia) was pulverized in a mortar until homogenous dark grey powder resulted. The powder was added to a mixture of elemental sulfur (1.86 g, 0.058 mol) and sodium sulfide nonahydrate (20.89 g, 0.087 mol). Approximately 20 cc of distilled water were added to the mixture. Then, the mixture was heated to the boiling point on a hotplate under vigorous stirring. Since mainly large particles of antimony(III) sulfide were used, the mixture was held at the boiling point for one hour. The resulting gold-yellow solution was filtered at atmospheric pressure while still hot and the solid residue was washed with a few cc of 5% sodium hydroxide solution. The solution was left freely for crystallization. After four hours, bright yellow crystals of the product were filtered off.

stibnite, sulfur, sodium sulfide

Reactants used for the synthesis of sodium thioantimonate

The resulting gold-yellow solution.

The resulting gold-yellow solution.

Discussion:

During the experiment,  slow dissolution of sulfur formerly present at the top of the solution was observed at low temperatures. By heating the mixture under constant stirring, sulfur disappeared in about 15 minutes and the solution turned yellow. At this time, still, remarkable amount of dark solid was present. Further heating and stirring did not let to complete dissolution of solid particles. These were filtered off and the resulting gold-yellow solution was let for crystallization. A big aggregate of bright yellow crystals settled at the bottom of the beaker after 3-4 hours. This was manually removed and the solution was let to stand overnight. The following day, only one big crystal with clearly distinguishable tetrahedral faces was found in the beaker. Its IR spectra are given below and compared to those of pure sodium sulfide.  The third crop of crystals was represented by several single crystals. However, some of them appeared to have octahedral shape and were not coloured. It may be presumed that unreacted sodium sulfide started to crystallize out of the saturated solution. It can be concluded that using natural source of antimony trisulfide for thioantimonate synthesis needs only 50% of original amount of reactants due to the presence of solid residue that does not react during the course of the reaction. Moreover, the usage of natural antimony trisulfide source demonstrates an easy way for preparation of rare tetrahedral crystals.

Na3SbS4_3

Aggregates of sodium thioantimonate crystals (first crop of crystals from the synthesis)

Tetrahedral crystal of sodium thioantimonate

Tetrahedral crystal of sodium thioantimonate

Graph1

IR spectra of sodium thioantimonate(V) comapred to the spectra of sodium sulfide

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