Editing Thallium (section)

===Organothallium compounds===
{{See also|Organothallium chemistry}}

Organothallium compounds tend to be thermally unstable, in concordance with the trend of decreasing thermal stability down group 13. The chemical reactivity of the Tl–C bond is also the lowest in the group, especially for ionic compounds of the type R<sub>2</sub>TlX. Thallium forms the stable [Tl(CH<sub>3</sub>)<sub>2</sub>]<sup>+</sup> ion in aqueous solution; like the isoelectronic [[dimethylmercury|Hg(CH<sub>3</sub>)<sub>2</sub>]] and [Pb(CH<sub>3</sub>)<sub>2</sub>]<sup>2+</sup>, it is linear. Trimethylthallium and triethylthallium are, like the corresponding gallium and indium compounds, flammable liquids with low melting points. Like indium, thallium [[cyclopentadienyl]] compounds contain thallium(I), in contrast to gallium(III).<ref name="Greenwood262">Greenwood and Earnshaw, pp. 262–264</ref>