Thallides are compounds containing anions composed of thallium. There are several thallium atoms in a cluster, and it does not occur as a single Tl⁻ in thallides.^[1][2] They are a subclass of trielides,^[2] which also includes gallides and indides.^[3] A more general classification is polar intermetallics, as clusters contain delocalized multicentre bonds.^[4] Thallides were discovered by Eduard Zintl in 1932.^[5]

Mixed anion compounds with thallides include halides (bromides and chlorides),^[6] oxides,^[7] and tetrelates (silicate, germanate).^[8]

Production

Thallide compounds can be produced by melting metals together in a tantalum crucible under an inert argon atmosphere.^[3] However if arsenic is included in the mix, it can react with the crucible wall.^[9]

A low temperature production route, is to dissolve an alkali metal in liquid ammonia, and use that to reduce a thallium salt, like thallium iodide.^[10]

Properties

Thallide compounds are dense, dense to X-rays and usually metallic grey or black in appearance.

Thallide clusters mostly do not follow Wade-Mingos rules or the Zintl–Klemm concept, as they have too small a negative charge. They can be called "hypoelectronic".^[11]

Reactions

In liquid ammonia, oxidation occurs yielding metal amides, and thallium metal.^[2]

Thallides react with water and air.^[2]

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