Thallium

The thallium(I) halides are stable. In keeping with the large size of the Tl+ cation, the chloride and bromide have the caesium chloride structure, while the fluoride and iodide have distorted sodium chloride structures. Like the analogous silver compounds, TlCl, TlBr, and TlI are photosensitive and display poor solubility in water. The stability of thallium(I) compounds demonstrates its differences from the rest of the group: a stable oxide, hydroxide, and carbonate are known, as are many chalcogenides.

The metalorganic compound thallium ethoxide (TlOEt, TlOC2H5) is a heavy liquid (ρ 3.49 g·cm−3, m.p. −3 °C),[24] often used as a basic and soluble thallium source in organic and organometallic chemistry.