The Systems Li-Tl, Na-Tl and K-Tl

It is a well-known and often-used heuristic in chemistry to compare properties of chemically related systems. In the present case, the physical chemistry of binary systems of thallium with alkali metals Li, Na and K are presented together to show similarities and differences. In each case, the literature was mined to retrieve original experimental data for the phase diagram, thermodynamic properties of solutions and compounds, structural information for compounds and effects of pressure. Special attention is given to the phase diagram, by plotting data and showing assessed phase boundaries. Whether stated by investigators or nor, mutual solid solubility of the components at the composition extremes was evaluated. In some cases, investigators omitted the presence of αTl (low temperature solid structure) in their reports. In these cases, the assessed phase diagrams include suggested possible phase boundaries to indicate the existence of two forms of solid Tl. Thallium is the heaviest member of the triel group of elements B → Nh (Group 13 new notation, Group IIIB old notation). These elements tend to form clusters or cages, as concluded from neutron diffraction measurements on liquid solutions (Verkerk et al. in J Phys Condens Matter 6(Suppl. 23A):A255–A260, 1994, Van der Aart et al. in Phys B 234–236:362–363, 1997, Van der Aart et al. in J Non-Cryst 250–252(Part 1):241–244, 1999). They may be represented by [Tln]m−, where n may take values from 4 to 13, and m from 5 to 11. The particular values of m and n depend on the number and identity of cations in the structure (Dong and Corbett in J Am Chem Soc 117(24):6447–6455, 1995, Corbett in Angew Chem 112(4):682–704, 2000, Wang et al. in J Am Chem Soc 134(48):19884–19894, 2012). The structures are described as “hypoelectronic” (electron-poor). This multiplicity of structures probably accounts for the fact that, in some systems, not all synthesized compounds appear in the phase diagram, and some may have mislabelled stoichiometries.