Complexes of Thallium

In contrast to the behavior of comparable aluminum, gallium, and indium compounds, the hitherto known alkynyl thallium(III) compounds (170) of the type R2T1C=CR show no tendency to dimerize via n complexation. Molecular weight determinations performed in aniline show the monomeric character of these species, which behave as weak electrolytes due to partial dissociation into R2T1+ and C=CR (170). 

Many cyclopentadienylthallium(I) compounds have been described in the literature the first one, cyclopentadienyl thallium (Lilia), was synthesized by Fischer and Hofmann (160) nearly 30 years ago. The colorless solid can be best prepared from cyclopentadiene and thallium hydroxide or thallium(I) salts in the presence of alkali in aqueous solution (171) [Eq. (11)]. The ring-substituted species LUIb-i (172,173,268,270) (Table V) as well as hydro- 

Many investigations have been performed in order to elucidate the structure and bonding in cyclopentadienylthallium(I) compounds. Various bonding situations are found in this class. The parent compound, cyclopentadienyl-thallium (LHIa) is nearly unsoluble in polar solvents. It is rather stable to air and water and sublimable in a vacuum. The microwave spectrum (178) suggests a half-sandwich structure in the gas phase with a thallium to ring centroid distance of 2.41 A (see Fig. 11). The thallium-carbon distances of 

71 A are smaller than the sum of the van der Waals radius of carbon and the ionic radius of Tl+ (3.1 A). The structure (164) of Lilia in the solid state contains linear polymeric chains, which are composed of alternating cyclo-pentadienyl rings and thallium atoms, a situation similar to that observed for cyclopentadienylindium(I). The difference between the thallium-ring distances in the gas phase and in the solid state is very great (171). 

In the H- and l3C-NMR spectra of Lilia no spin-spin coupling between 205TI and or 13C nuclei has been observed (172). Apparently there is 

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A large number of halide complexes of thallium(III) have been prepared by precipitation of the complexes from solution with a suitable cation, eg, H+, (C2H5)4N+, (C6H5)4As+, and K+. Both four-coordinated [HXJ" and six-coordinated [TlXJ3 ions exist in solutions and in solid states. 

Complexes of Thallium(I) with Other Anionic Ligands... 

A tris(imidazolyl)borate (138) complex of thallium(I) has been synthesized.The solid-state structure of hydrotris(imidazolyl)boratothallium(I) consists of one-dimensional, twisted, ladderlike strands, and three-coordinate thallium centers. Due to the position of the nitrogen donors, the tris(imidazolyl)borate ligand is not capable of forming metal chelates as are observed in tris(pyrazolyl)borates. Poly(benzotriazolyl)borate ligands have some features of both tris(pyrazo-lyl)borate and tris(imidazolyl)borate systems. Thallium(I) complexes of bis-, tris-, and tetrakis (benzotriazolyl)borates are reported. These adducts have been synthesized by treating the corresponding potassium derivative with an equimolar quantity of thallium(I) formate. ... 

Mixed-metal alkoxide complexes of thallium are also known. For example, Sn(/u-t-BuO)3Tl has both Sn(II) and T1(I) ions." The thallium site is unreactive as a donor for metal carbonyls. However, as indicated earlier, the indium(I) site of the indium analogue shows Lewis-base character. The Sn(IV)/Tl(I) mixed alkoxide [Sn(EtO)eTl2] exists as a one-dimensional polymer. This adduct reacts quantitatively with SnCl2 to form the homoleptic, mixed-valent [Sn2(OEt)6]n. Thallium-titanium double alkoxides have been synthesized using thallium alkoxide as one of the starting materials. ... 

Extraction of the chloride complex of thallium(III) from HCl media is less selective [4-6]. For diethyl ether and DIPE, the most suitable media are 4 M HCl and 6 M HCl, respectively. Au(III), Fe(III), Sb(V), Sn, Hg, Mo, As, Ge, and Ga are partly extracted along with the thallium(III) from an HCl medium. Extraction of Tl(lII) from less concentrated HCl media by using CHCI3 solutions of n-octylaniline has been proposed [7]. 

The halide complexes of thallium(III) in aqueous solution are among the most stable of metal halide complexes, and they have been intensively studied (3, 89-92,103,118-122). There occurs a distinct break... 

These spectral features and other evidence presented in this paper (97) leave no doubt that the Tl(III) cyano complexes exist, that they have the stated composition, and that they are extremely strong and kinetically inert. In fact, the cyano complexes are stronger than any other known monodentate complexes of thallium(III). The only possible known competitor as a ligand, the iodide ion, forms the complex TII4 with the overall stability constant log = 35.7 (99), i.e., several orders of magnitude lower than that of T1(CN)4" (see Table III). The distribution of thallium among the various Tl(CN), "-species is shown in Fig. 5. Stepwise stability constants of MX complexes often decrease with increasing n because of statistical, steric, and coulombic factors... 

FIGURE 9.25 Complexes with Coordination Number 2. (a) Linear Au in [EtjPAuTilCOjg]". Note that this structure features 2-coordinate gold and 7-coordinate titanium, (b) A )3-diketiminate complex of thallium, (c) The result of a novel strategy for low coordinate iron that features dative Fe—Fe bonding. (Molecular structure drawings created from CIF data with hydrogen atoms omitted for clarity.)... 

Calix[4]arene probe 29 [57] (Fig. 28.7), in 1,3-altemate conformation and containing bis(crown-6-ether) and a dansyl group, showed selectivity for thallium (1). The fluorescence titrations of 29 with thallium(I) were performed at pH 3.5, at which the probe is in its midissociated form. The complexation of thallium(I) to probe 29 results in slight quenching and blue shift of the fluorescence emission. This behavior was attributed to both PET in the complex and NH-proton displacement by thallium(I). 

E.A. (1970) Spectrophotometric study of hydroxo-complexes of thallium(I). Russ. 

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