Dehydration of Solid SnCl 2 ( OH 2 ) • H 20 to SnCl

Crystalline stanous chloride dihydrate (SCD), more descriptively named dichloroaquatin(II) monohy­ drate SnCl2(OH2) • H20 [1, 2], is not a very stable compound. The vapour pressure of its crystal water is appreciable already at room temperature. If the com­ pound is stored in a dry atmosphere or under vacuum it quickly loses water and becomes highly reactive at its surface. One of the usual methods to obtain anhydrous SnCl2 powder from polycrystalline SCD is chemical reaction with liquid acetic anhydride [3] followed by purification. Simple drying at elevated temperatures is not recommended because then the product is likely to be unpure owing to partial surface oxydation [4]. Here we present a study of the dehydration of SCD in a stream of a pure inert gas at room temperature and below. There are several possibilities to observe this reaction. The simplest is measurement of the weight loss. Alternative methods are measurement of the disappearing proton NMR signal or measurement of the appearing chlorine NQR signals. The latter method was used here. SnCl2(OH2) • H20 gives no NQR signal. SnCl2 samples obtained by the acetic anhydride method [3] exhibit the same chlorine NQR lines as samples dried in an inert gas stream, though the former lines are sharper.