Preparation of Pentaindium Tetrasulfide in Liquid Tin

In the indium-sulfur system the phases InS1, In S72, and three allotropic forms of In2S33 4 5 have been identified and their structures analyzed. All of these compounds have been prepared by conventional methods, that is, direct combination or transport reaction techniques. By using molten tin as a solvent, a new metal-rich combination was obtained. The material is electrically insulating and diamagnetic at room temperature. 

I Caution. Proper shielding should be used when heating sealed tubes. Mixtures of indium, sulfur and tin, all of high purity, are sealed in evacuated transparent silica tubes. The In S ratio should be close to 1 1, and excess tin, four times the weight of the reactants, is added. This is close to the solute-to-solvent ratio that was found to give the best crystalline yield in the preparation of gallium monochalcogenides.6 The tubes are heated at a constant rate of 50°/ hr up to temperatures of 650-1100°. 

To assure complete dissolution of the elements, the reactants are held at the maximum temperature for a few hours before the temperature decrease is started. 

After having reached room temperature the ampoules are cut open and the reaction products further treated. The products obtained (of which three main types can be distinguished) are found to be highly dependent on the cooling program. 

A high maximum temperature ( 1100°) is found to give the best yield of the products. The lowest temperature that yields InsS4 is 650°. To isolate the reaction products from the tin matrix, the chunks of reacted material are treated with concentrated hydrochloric acid. To reduce the attack on the crystals, short-time treatments with acid are alternated with acetone washings. 

---