Thallium selenates

Vojtisek and Ebert [89VOJ/EBE] determined the solubility of Tl2Se04(cr) in water at 

15 K to be 0.0588 molkg as part of a study of the system Tl2Se04-MgSe04-H20. 

Selivanova [58SEL] calculated thermodynamic quantities for Tl2Se04(cr) at 

15 K from solubilities interpolated in an unknown way from data in the literature, see Appendix A. No experimental value of the solubility at 298.15 K was available then. As the solubility data surrounding the standard temperature were obtained at 293 and 353 K, her results were checked by calculating the solubility product from data available at 282.5, 285.2, and 293.2 K. Activity coefficients were estimated by SIT with s(Tr, Se04 ) = e(K, SeO ) = -0.06 kg-mol . The linear log, f(l/7 ) plot was extrapolated to 298.15 K and the solubility product of the reaction 

The standard Gibbs energy of formation of thallium(l) selenate is calculated from the solubility product and the Gibbs energies of the ions (AfG° (Tr, 298.15 K) = - (32.40 0.30) kJ moE [99RAR/RAN]) to be  

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Assoziation in der Dampfphase bei Aktivitatsbestimmungen und Revision der Aktivitaten fliissiger Legierungen der Systeme Selen-Thallium, Selen-Wismut und Selen-Antimon, Z Metallkd, 70, (1979), 109-112, in German. Cited on page 250. 

The physical properties of the metal (Table II) resemble those of thallium, lead and bismuth, its neighbors in the Periodic Table, rather than those of tellurium, its lower homologue. The low melting and boiling points are particularly noteworthy an attempted study of the Hall effect in polonium metal has also been reported (90). In chemical properties the metal is very similar to tellurium, the most striking resemblance being in its reactions with concentrated sulfuric acid (or sulfur trioxide) and with concentrated selenic acid. The products are the bright red solids, PoSOs and... 

In addition to the halide systems there are a number of thallium(I) salts of thallium(III) complex anions in which the overall stoichiometry implies, incorrectly, the presence of thallium(II) species. These include the sulfate, selenate,369 acetate370 and oxalate371 derivatives. An X-ray determination has confirmed that Tl(OAc)2 is indeed Tl[Tl(OAc)4], in which the anions are linked through seven-coordinate Tl+, with some evidence for a stereochemically active inert pair.370 In T1[T1(0H)(S04)2], the structure consists of sheets of linked anions with Tl+ ions.372... 

Several molecular structures, including those of T1(I) nitrate," " iodate," " borate," germ-anate," sulfate, " phosphates, arsenate, chromate," and selenate," have been reported. Heterobimetallic compounds with Tl-0 interactions have been reported. Their metal-thallium bonding and their photophysical properties are of particular interest. 

The standard Gibbs energy of formation of thallium(lll) selenate is reported as AfG° (Tl2(Se04)3, cr, 298.15 K) = -901.1 kJ-mol" in [82WAG/EVA]. The source of this datum could not be traced and it has therefore not been selected. No other data have been found for this compound. 

A number of other inorganic compounds of trace elements, such as barium silicofluoride CBaSiFg), sodium selenate (NaSeOi ) and thallium sulfate CTlaSOi ) have occasionally been used as insecticides, but their use is so limited, it cannot make any significant contribution to dispersion of trace elements in the soil. 

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