Lattice energy thallium halides

Because of the difficulty of assigning basic radii in some crystals, notably those of the halides of silver and thallium, Ladd and Lee (7 ) have extended the above expression, which eliminates B and hence the basic radii, to the case where other forces, that is, dispersion energy terms, are included. They obtain for the lattice energy Uo... 

The crystal structures of the three heavier thallium(I) halides have been established and lattice energies calculated the inert pair of T1+ is apparently insignificant in terms of the stability of the lattice. The enthalpy of hydration of the Tl ion was also derived. Gas phase (TlBr, Til) and matrix isolation studies (TlCl, TlBr, Til) have shown that TlX and TI2X2 species are important.Complex formation in aqueous solution decreases in the order Cl > Br > I, and as with the fluorides, the double salts show no evidence of anionic complex formation by Tl Finally, it is important to note that TII3 is formulated as Tr(lT) from X-ray studies.Thermal decomposition yields TI3I4, whose structure has not been reported. 

Similarly, the lattice energy—which is determined experimentally from the heat of sublimation—is also susceptible to theoretical estimation. To obtain good agreement, one must, of course, take into consideration the exchange forces of the electron shells in close proximity and the zero energy in addition to the two purely electrostatic terms of equation (34). J. Mayer has done this for the halides of thallium and silver and has found very satisfactory agreement with experimentally determined data. Table 59 is a proof of this. 

A Comparison of Born-Haber and Born-Lande Lattice Energies for Sodium, Silver, and Thallium Halides... 

The presence of lattice defects and/or intentionally placed impurities in the alkali halide crystal will cause the formation of local energy levels in the forbidden gap, called traps or activator centers. Figure 18.19 shows the energy levels of an alkali halide crystal, including the activator centers and traps. (Atomic thallium is a common activator for alkali halide crystals.)... 

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