Thallium complexes, stability

A similar model for the case of thallium cuprate is complicated by the large number of parameters that affect the state of the system, and also by the necessity to introduce two experimentally unknown quantities simultaneously into the model. However, taking into account the character of the pH dependences of all the processes that occur with the participation of thallium and copper, one can suppose that the shape of the thallium cuprate stability region would be close to that for the mixed oxide. That is, its width would increase with increasing concentration of copper ions (hydroxo complexes) within the crystallization zone. Although the crystallization process took place under a fortiori non equilibrium conditions, the results of the preparative analysis agree qualitatively with the concept of stability of the products. The interval over which formation of thallium cuprate on copper substrates occurs and the formation of the mixed oxide on platinum and carbon substrates can be observed is wider for higher values of the pH [352-354]. 

The level of soluble thallium present in the sea (e.g. Pacific Ocean, Atlantic Ocean, Irish Sea, Australian Coast) is between 9 and 16 ng/L (Matthews and Riley, 1970). This is remarkably lower than in fresh waters. In natural sea water (pH 8.1), the oxygen content is sufficient to oxidize Tl(l) to Tl(lll). because formation of chloro-complexes stabilizes the trivalent state. In the Pacific Ocean, 80% of the thallium was found to occur as Tl(lll), and only 20% as the sum of Tl(l) and alkylthallium compounds (Batley and Florence, 1975). As Tl(lll) is easily adsorbed and coprecipitated, it continuously moves down to the sediments. 

Contrary to In3+, the heaviest d acceptor of group 3B, Tl +, is a very soft acceptor, as is evident from the stabilities of its chloride and bromide complexes (Table 2). The lower iodide complexes are not stable relative to the redox reaction producing thallium(I) and free iodine. The inherent affinity of T13+ for 1 is so strong, however, that even at rather modest concentrations of free iodide, thallium (III) is completely protected from reduction by formation of the complex Tlli (80). The value... 

The pseudohalides and related compounds have been investigated by a number of workers. Thallium(I) cyanate and thiocyanate are both known, and the latter has been shown to be ionic in the solid state 288 differing values have been reported for the stability constants in the T1/NCS system in aqueous or mixed water/non-aqueous systems, but the overall evidence is that the complexes are extremely weak.289 The ionic selenocyanate has been reported, but the chemistry has not been investigated.1... 

Stability constant studies show that in aqueous solution the anions T1FJ, T1F2- and T1F4 are formed 289 some of these may be aquated. Many double salts have been reported,1 but it seems that thallium is present in these as the Tl+ cation rather than as TLF0 I+,) anionic complexes. 

Literature values for stability constants (153) have usually been determined for solutions much less concentrated than those needed for diffraction measurements, and the values for these solutions have to be checked by other methods. For the thallium(III) bromide complexes the stability constants for the concentrated solutions used [1-2.6 M in Tl(III)], were derived from Tl-205 NMR shift measurements. The fraction of Tl(III), bonded in each of the complexes calculated from these constants as a function of the chloride concentration (Fig. 17), shows... 

The atoms of the chemical elements, are, as I have already said, extremely complex, but their structure is not yet completely understood. To some part of each kind of atom its chemical properties and its spectrum are probably due. It is conceivable that this part may be the earliest to form, with its surrounding rings or envelopes at first not quite adjusted to permanent stability. With the final adjustment the isotopes as such should disappear, and the normal element be completed. This is speculation, and its legitimacy remains to be established. A careful comparison of the spectra of the elements from thallium up to uranium might furnish some evidence as to its validity. The spectrum of uranium, for example, may contain lines which really belong to some of its derivatives. 

TI+/TI(Hg) electrode — A -> reference electrode commonly known as Thalamid electrode employing thallium amalgam (40wt%) as electronically conducting phase and an aqueous solution of KC1 (saturated or 3.5 M) saturated with T1C1. In comparison with the saturated calomel electrode it shows a superior temperature stability up to T = 135 °C without temperature hysteresis, no disproportionation of T1C1 (as compared to Hg2 CI2) or significant complexation are found. 

Thallium(I) halides are predominantly ionic, although there is a tendency toward increasing covalent character in the series of compounds TlCl (17%), TlBr (20%), and TII (28%). This increased degree of covalency results in decreased solubility for example, TIF is soluble in water whilst the other Tl halides are only sparingly soluble. The thallium(I) halides are classical examples of incompletely dissociated 1 1 electrolytes. The stability of halide complexes of Tl is low and follows the order TIF < TlCl < TlBr < TII, where for the series of halides, Kx = -, 0.8, 2.1, 5.0 and Ki = -, 0.2, 0.7, 1.5 respectively. The fluoride ion F is preferred to perchlorate as a noncomplexing counterion. Claims have been made for T1X species with n = 3 and 4 however, the formation of complexes in aqueous solution with n > 2 seems unlikely. 

Metal aUcoxide complexes with related alcohols are apparently edge-sharing bioctahedral dimers, on the evidence of the X-ray stmcture of the isopropyl complex. Some stable mixed alkoxides of the type Q[M3(OR)9] (Q = Li, Na, K, NH4, Ca/2) have been reported they distill in vacuo without decomposition. The X-ray stmctures of several bimetallic alkoxides obtained by Caulton,QZr2[0(/-Pr)]9,Q = Li[HO(i-Pr)], K(DME), Ba[0(i-Pr)], show a similar triangular stmcture with two 743 and three /r-OR bridges. The thallium salt of composition Tl2Zr((/R)6 obtained by the reaction shown in equation (18) has a distorted octahedral stmcture stabilized by six T1 F contacts. ... 

Sutton (666) and Kul ba (458-460) have prepared a number of bipyridyl and phenanthroline complexes of various thallium(III) salts those with nitrate and perchlorate are generally bis-chelate compounds, whereas the halides give compounds of stoichiometry TIX3L. Stability constants have been reported for some of the complexes (457). Other mixed ligand species containing ethylenediamine (461) and oxalate (456) and salts containing both bipyridyl and phenanthroline coordinated to the same thallium(III) ion (456) are also claimed. 

A detailed, multimethod study of hydrated Tl(III) cyanide species in aqueous solution reveals that Tl(III) forms very strong complexes with cyanide ions (even stronger than halide-Tl(III) interactions)." " Formation of a series of Tl(III) complexes T1(CN) n= -4t) has been established, and the solution structures and stability constants were reported. The mono- and dicyano complexes [Tl(CN)(OH2)5] and [Tl(CN)2(OH2)4] show six-coordinate thallium centers, whereas Tl(CN)3(OH2) and [T1(CN)4] have four-coordinate T1(III) ions. 

Stability of organo-mercury, -thallium, -tin and -lead complexes with anionic and neutral ligands... 

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