Synthesis and characterization of four new thallium(I) tetrazole supramolecular compounds with various secondary interactions; new precursors for thallium(III) oxide nano-particles

Four new thallium(I) coordination polymers, [TlBt](n) (1) (Hbt = 5-phenyltetrazole), [TlBbt] (2) (Hbbt = 5-(4-bromobenzyl)tetrazole), [Tl(2)Bdt](n) (3) (H(2)bdt = 5,5'-benzene-1,4-diylbistetrazole), [Tl(2)Pht·H(2)O](n) and [TlBet] (4), (Hbet = 5-(benzyl)tetrazole) have been synthesized and characterized. The single-crystal X-ray data shows that, in compounds 1-3, the coordination sphere of the Tl(I) ion is the same and it is surrounded with six tetrazolate rings. In compound 4, one thallium atom has three interactions with tetrazolate groups and close Tl(I)···π (aromatic) contacts with the phenyl ring. Furthermore, in all cases the single-crystal X-ray data show the same stereo-chemical activity of the valence shell electron lone pair of Tl(I). There is a strong Tl(I)···Tl(I) interaction in one dimension in compounds 1 and 3. All these four compounds have been used as new precursors for the preparation of thallium(III) oxide nano-particles through a simple calcination method. Thallium(III) oxide was characterized by powder XRD diffraction and the morphology of nano particles characterized by scanning electron microscope (SEM).     

Solubility, complex formation, and redox reactions in the Tl2O3-HCN/CN(-)-H2O system. Crystal structures of the cyano compounds Tl(CN)3.H2O, Na[Tl(CN)4].3H2O, K[Tl(CN)4], and Tl(I)[Tl(III)(CN)4] and of Tl(I)2C2O4

Thallium(III) oxide can be dissolved in water in the presence of strongly complexing cyanide ions. Tl(III) is leached from its oxide both by aqueous solutions of hydrogen cyanide and by alkali-metal cyanides. The dominating cyano complex of thallium(III) obtained by dissolution of Tl2O3 in HCN is [Tl(CN)3(aq)] as shown by 205Tl NMR. The Tl(CN)3 species has been selectively extracted into diethyl ether from aqueous solution with the ratio CN-/Tl(III) = 3. When aqueous solutions of the MCN (M = Na+, K+) salts are used to dissolve thallium(III) oxide, the equilibrium in liquid phase is fully shifted to the [Tl(CN)4]- complex. The Tl(CN)3 and Tl(CN)4- species have for the first time been synthesized in the solid state as Tl(CN)3.H2O (1), M[Tl(CN)4] (M = Tl (2) and K (3)), and Na[Tl(CN)4].3H2O (4) salts, and their structures have been determined by single-crystal X-ray diffraction. In the crystal structure of 1, the thallium(III) ion has a trigonal bipyramidal coordination with three cyanide ions in the equatorial plane, while an oxygen atom of the water molecule and a nitrogen atom from a cyanide ligand, attached to a neighboring thallium complex, form a linear O-Tl-N fragment. In the three compounds of the tetracyano-thallium(III) complex, 2-4, the [Tl(CN)4]- unit has a distorted tetrahedral geometry. Along with the acidic leaching (enhanced by Tl(III)-CN- complex formation), an effective reductive dissolution of the thallium(III) oxide can also take place in the Tl2O3-HCN-H2O system yielding thallium(I), while hydrogen cyanide is oxidized to cyanogen. The latter is hydrolyzed in aqueous solution giving rise to a number of products including (CONH2)2, NCO-, and NH4+ detected by 14N NMR. The crystalline compounds, Tl(I)[Tl(III)(CN)4], Tl(I)2C2O4, and (CONH2)2, have been obtained as products of the redox reactions in the system.     

Syntheses and characterization of thallium(I) complexes with 3-nitrophenoxide [Tl(3-np)], 4-nitrobenzoate [Tl(4-nb)] and 2,4-dinitrophenoxide [Tl(2,4-dnp)]: X-ray crystal structures of [Tl(3-np)]n and Tl(2,4-dnp) (two new polymeric compounds)

Complexes thallium(I)3-nitrophenoxide [Tl(3-np)], thallium(I)2,4-dinitrophenoxide [Tl(2,4-dnp)] and thallium(I)4-nitrobenzoate [Tl(4-nb)] have been synthesized using a direct reaction between TlNO₃ and the appropriate ligand. The complexes have been isolated and characterized by IR spectra and CHN elemental analyses. The structures of [Tl(3-np)]_n and [Tl(2,4-dnp)] have been confirmed by X-ray crystallography. The single crystal X-ray crystallography of [Tl(3-np)]_n shows the complex to be a one-dimensional polymer as a result of bridging 3-nitrophenoxide ligands. The Tl atoms have an unsymmetrical three-coordinate, O₃ geometry (three oxygen atoms of the 3-nitrophenoxide ligand). The crystal structure of [Tl(2,4-dnp)] shows the complex to be a three-dimensional polymer as a result of bridging 2,4-dinitrophenoxide ligands. The Tl atoms have an unsymmetrical two-coordinate, O₂ geometry (two oxygen atoms of the 2,4-dinitrophenoxide ligand). The arrangement of the 3-nitrophenoxide and 2,4-dinitrophenoxide ligands suggests a gap in coordination geometry around the Tl(I) ions, occupied possibly by a stereoactive lone pair of electrons on Tl(I). There is a π–π stacking interaction between the parallel aromatic rings belonging to adjacent chains in the compounds that may help to increase the ‘gap’ in coordination geometry around the Tl(I) ions.     

Double-stranded metal-organic networks for one-dimensional mixed valence coordination polymers

The design of new types of metal-organic networks and the search for unusual crystal architecture represents an important task for modern inorganic and materials chemistry research. A group of new monosubstituted phenylcyanoximes, containing F, Cl, and Br atoms at the 2, 3, or 4 positions, were synthesized using the high yield nitrosation reaction with CH3-ONO and were spectroscopically (1H NMR, 13C NMR, UV-visible, IR, mass spectrometry) and structurally characterized. Results of X-ray analysis revealed nonplanar trans-anti geometry for 2-chlorophenyl(oximino)acetonitrile, H(2Cl-PhCO); a nonplanar anti configuration for 4-chlorophenyl(oximino)acetonitrile, H(4Cl-PhCO); and planar cis-syn geometry for 3-fluorophenyl(oximino)acetonitrile, H(3F-PhCO). All arylcyanoximes undergo deprotonation in solutions with the formation of colored anions exhibiting pronounced negative solvatochromism in a series of polar protic and aprotic solvents. Nine thallium(I) cyanoximates were obtained using the reaction between hot (approximately 95 degrees C) aqueous solutions of Tl2CO3 and solid powdery monohalogenated arylcyanoximes HL. Crystal structures of two Tl(I) cyanoximates [Tl(2Cl-PhCO) and Tl(4Br-PhCO)] contained centrosymmetric dimeric units (TlL)2 that are connected to a coordination polymer by means of an oxygen atom of the oxime group of the neighboring molecule. Cyanoxime anions act as bridging ligands in both structures where the polymeric motif consists of double-stranded Tl-O chains interconnected with the formation of zigzagging Tl2O2 planar rhombes. Thallium atoms form infinite linear arrays with close intermetallic separations. The nearest Tl(I)...Tl(I) distances are 3.838 and 4.058 angstroms in the Tl(2Cl-PhCO) and Tl(4Br-PhCO) structures, respectively, close to that in metallic thallium (3.456 angstroms). Monosubstituted phenyl groups are well aligned in pi-stacking columns that are perpendicular to the array of Tl(I) atoms and stabilize formed structures. Coordination polyhedrons of thallium(I) in these complexes represent distorted trigonal pyramids with stereoactive lone pair.     

Synthesis, Properties, and Crystal Structures of Benzene-1,2-dithiolato Complexes of Thallium(I) and -(III)

The syntheses, molecular structures and properties of homoleptic 1,2-S(2)C(6)H(4) complexes of thallium(I) and thallium(III) with four-coordinated metal centers are described. Anaerobic treatment of TlCl, TlNO(3), or Tl(2)CO(3) with solutions of sodium methanolate and 1,2-(HS)(2)C(6)H(4) in methanol gave after metathesis with [NEt(4)]Br yellow solutions of [NEt(4)](2)[{Tl(1,2-(&mgr;-S)(2)C(6)H(4))}(2)] ([NEt(4)](2)1). Yellow single crystals were obtained from saturated acetone solutions at -10 degrees C and the crystal data for [NEt(4)](2)1 are monoclinic, P2(1)/c, with Z = 2, a = 7.440(1) ?, b = 16.373(3) ?, c = 13.201(2) ?, and beta = 97.08(1) degrees. Complex 1(2)(-)(), the first structurally characterized homoleptic ionic thiolate complex of thallium(I), contains rectangular bipyramidal [TlS(4)Tl] cages with the four sulfur atoms defining the equatorial plane and the two thallium atoms in axial positions. The S(2)C(6)H(4) fragments are almost coplanar with the S(4) plane. In the crystal lattice, nearly linear Tl.Tl chains align along the a-axis (offset ca. 3.0 degrees ) with the ligand planes parallel to the bc-plane. Within and between dimers short Tl.Tl distances are observed (Tl.Tl' within a dimeric unit, 3.5116(4) ?; Tl.Tl between dimeric units, 3.9371(3) ?) with the distance between dimeric units being the shortest contact between anions-Tl.S distances between dimeric units are longer than 5.8 ?. Aerobic treatment of TlCl, TlNO(3), or Tl(2)CO(3) with solutions of sodium methanolate and 1,2-(HS)(2)C(6)H(4) in methanol and metathesis with [NEt(4)]Br led to [NEt(4)][Tl(1,2-S(2)C(6)H(4))(2)] ([NEt(4)]2). Yellow single crystals were obtained from saturated acetone solutions at 0 degrees C and the crystal data for [NEt(4)]2 are orthorhombic, Pnn2, with Z = 2, a = 11.449(2) ?, b = 10.060(2) ?, c = 9.950(2) ?. Complex 2(-) is the first homoleptic four-coordinate thiolate of thallium(III) and contains the unusually short Tl-S distance of 2.469(4) ?. In solution, ion pairing results in chemical and magnetic inequivalence of the S(2)C(6)H(4) ligands. Although both preparations employ the reaction of thallium(I) salts with 1,2-(NaS)(2)C(6)H(4) in a 1:2 stoichiometry, complex 1(2)(-) is probably not an intermediate to the formation of 2(-). Exposing anaerobically prepared solutions of 1(2)(-) to air results in a series of color changes in the solution over a 20 min period; however, 2(-) could not be observed by NMR spectroscopy.     

Iodophthalocyaninato(2–)thallium(III) – Synthese und Kristallstruktur

Iodophthalocyaninato(2–)thallium(III) – Synthesis and Crystal Structure Oxidation of dithalliumphthalocyaninate(2–) with excess iodine yields crystalline, blue-green iodophthalocyaninato(2–)thallium(III). It crystallizes in the orthorhombic space group Pnma (no. 62) with lattice parameters: a = 13.778(3) Å, b = 14.649(2) Å, c = 14.907(1) Å, Z = 4. The Tl atom coordinates four N_iso atoms (isoindole N atoms) and one I atom in a tetragonal pyramidal arrangement. The Tl atom is located out of the centre of the (N_iso)₄ plane towards the iodine atom by 0.959(3) Å. The Tl–I distance is 2.674(1) Å, the Tl–N_iso distances range from 2.20(1) to 2.23(1) Å (average 2.22(1) Å). The phthalocyaninate(2–) is severely distorted from planarity (concave distortion).     

Vanadium(III) as an analytical reagent: The titrimetric determination of iron, copper, thallium, molybdenum, uranium, vanadium, chromium and manganese

Vanadium(III) solutions can be used in direct titrations of iron(III), copper(II), thallium(III), molybdenum(VI), uranium(VI), vanadium(V), chromium(VI) and manganese(VII) in milligram amounts. The titrations are done at 70-80 degrees for iron(III), copper(II), thallium(III), molybdenum(VI) and at room temperature for vanadium(V), chromium(VI) and manganese(VII). Uranium(VI) is titrated at 70-80 degrees in presence of iron(II). The vanadium(III) solution is prepared by reduction of vanadium(V) to vanadium(IV) with sulphur dioxide, followed by addition of phosphoric acid and reduction with iodide, and is reasonably stable.     

Thallium(I) Tropolonates: Synthesis,Structure, Spectral Characteristics,and Antimicrobial Activity Compared to Lead(II) and Bismuth(III) Analogues

Synthesis, single-crystal X-ray determination diffraction and FT-IR, NMR (¹H, ¹³C, ¹⁹F and ²⁰⁵Tl), UV–vis, and luminescence spectra characteristics were described for series of thallium(I) compounds: thallium(I) triflate (Tl(OTf)), 1:1 co-crystals of thallium(I) triflate and tropolone (Htrop), Tl(OTf)·Htrop, as well as simple thallium(I) chelates: Tl(trop) (1), Tl(5-metrop) (2), Tl(hino) (3), with Htrop, 5-methyltropolone (5-meHtrop), 4-isopropyltropolone (hinokitiol, Hhino), respectively, and additionally more complex {Tl@[Tl(hino)]₆}(OTf) (4) compound. Comparison of their antimicrobial activity with selected lead(II) and bismuth(III) analogs and free ligands showed that only bismuth(III) complexes demonstrated significant antimicrobial activity, from two- to fivefold larger than the free ligands.     

Thallium(I) -bis(trimethylsilyl) amid

The reaction of LiN(SiMe₃)₂ With TlCl in toluene yields the bis(trimethylsilyl)amino derivative of thallium(I) (1). In the gaseous phase and in benzene solution the compound is mainly monomeric, whereas in the solid state the amide 1 consists of cyclic dimers, which are linked to infinite chains by intermolecular Tl Tl contacts.     

A modified method of separating Tl(I) and Tl(III) in aqueous samples using solid phase extraction

In spite of the development of new measurement techniques in recent years, the rapid and accurate speciation of thallium in environmental aqueous samples remains a challenge. In this context, a novel method of solid phase extraction (SPE), involving the anion exchange resin AG1-X8, is proposed to separate Tl(I) and Tl(III). In the presence of diethylene triamine pentacetate acid (DTPA), Tl(III) and Tl(I) can be separated by selective adsorption of Tl(III)-DTPA onto the resin, Tl(III) is then eluted by a solution of HCl with SO₂. The validity of this method was confirmed by assays of standard solutions of Tl(I) and Tl(III). The proposed method is shown to have an outstanding performance even in solutions with a high ratio of Tl(I)/Tl(III), and can be applied to aqueous samples with a high concentration of other electrolytes, which could interfere with the measurement. Portable equipment and reagents make it possible to use the proposed method routinely in the field.     

Synthesis and Solid-State Structure of 2,6-Trip2C6H3Tl (Trip=2,4,6-iPr3C6H2): A Monomeric Arylthallium(I) Compound with a Singly Coordinated Thallium Atom

A “one-legged thallium” is observed in the arylthallium(I ) compound 2,6-Trip₂C₆H₃Tl (Trip=2,4,6-iPr₃C₆H₂), which was synthesized from the corresponding organolithium compound and thallium chloride. X-ray structure analysis reveals that 2,6-Trip₂C₆H₃Tl is monomeric in the solid state and contains a singly coordinated thallium atom (see space-filling model on the right).     

Features of EPR spectra of complexes of ortho-benzoquinones with Tl(I) and Tl(III) diethyldithiocarbamates

A study has been made of the EPR spectra of Tl(l) and Tl(III) o-semiquinolates, obtained by the interaction of o-benzoquinones with thallium amalgam and thallium(III) diethyldithiocarbamate, respectively. A strong temperature dependence has been found for the constant of hyperfine coupling (HFC) with the metal nucleus in thallium(III) 3,5-di-tert-butyl-o-semiquinolate; this is explained by the presence of competing mechanisms of spin transfer from the o-semiquinone ligand to the metal. Cation exchange and effective complexation of the Tl(I) o-semiquinolate with thallium diethyldithiocarbamate have been observed. The kinetic parameters of exchange have been determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 786–790, April, 1990.     

Anodic stripping voltammetric determination of thallium as [TlBr4]-rhodamine B complex

The anodic stripping voltammetric behaviour of the [TlBr₄]-rhodamine B complex is described and compared with that of thallium(I) and thallium(III) ions. The electrolyte composition, the best potential for the deposition of thallium from the complex in the selected electrolyte, the duration of the electrolysis, and the possibility of reduction of thallium in the [TlBr₄]-rhodamine B complex before the electrolysis with ascorbic acid were investigated. The results showed good reproducibility of the measurements of thallium as [TlBr₄]-rhodamine B complex and are similar to those obtained for thallium as Tl(I) and Tl(III) ions. As the [TlBr₄]-rhodamine B complex is strongly adsorbed on polyethylene, a previous preconcentration step on a column, packed with polyethylene powder, allowed the voltammetric determination of thallium as [TlBr₄]-rhodamine B complex in samples of KCl and NaCl as solid salts after the separation of the matrix. With this procedure it was possible to reach enrichment factors of 25 with recoveries from 96.7 to 107.9% for thallium concentrations from 5 to 40 μg L^–1 and RSD between 4.2 and 9.2%. The procedure was used to determine thallium traces in KCl and in sea salt. The results of these determinations were compared with the results obtained by graphite furnace atomic absorption spectrometry.     

Catalytic Determination of Perchlorate Using a Modified Carbon Paste Electrode

Abstract

A method for the catalytic voltammetric determination of perchlorate using a carbon paste electrode modified with a liquid anion exchanger is presented. The fundamental catalytic effect is based on the chemical reoxidation of electrochemically generated Tl(O) by perchlorate which can be monitored by an increase of the corresponding current flow. Perchlorate can be preconcentrated, together with tetrachlorothallate(III) as a catalyst, from hydrochloric acid solutions onto the modified carbon paste electrode under open circuit conditions. For analytical purposes, the increase of the current response for the reoxidation of Tl(O) to Tl(I) is exploited for quantifications. Methodical parameters such as pH, ionic strength of the media, preconcentration time and thallium concentration are investigated; the influence of interferents is studied. The dependence of the current increase on the concentration of perchlorate with different accumulation times is presented. The detection limit (3σ) is 50 μg˙l^?1 ClO₄ ^? (12 min accumulation). To show the applicability of the method to the analysis of real samples spiked drinking water was investigated.     

Studies on spectrophotometric methods of thallium determination

Eight sensitive methods of spectrophotometric determination of thallium have been studied and compared experimentally. The comparative criteria were: molar absorptivity, colour contrast of the basic reaction, working concentration interval and practical determination limit for thallium, precision of the method (the standard deviation), and selectivity. According to these criteria the best methods of extraction-spectrophotometric determination of thallium are those using Brilliant Green, Crystal Violet, Methyl Violet and Rhodamine B. The sensitivity depends very much on the oxidant used for conversion of Tl(I) into Tl(III). The oxidants suitable for each of the recommended methods are discussed.     

Speciation Analysis of Thallium by Reversed‐phase Liquid Chromatography ‐ Inductively Coupled Plasma Mass Spectrometry

An inductively coupled plasma mass spectrometer (ICP‐MS) was used as a liquid chromatographic detector for the speciation analysis of thallium in environmental samples. In this study, ionic thallium species, namely Tl(I) and Tl(III) were well separated by reversed‐phase high performance liquid chromatography (RP‐HPLC) with a C8‐HPLC column as the stationary phase and 1 mmol L^?1 tetrabutylammonium phosphate (TBAP), 2 mmol L^?1 diethylenetriamine pentaacetic acid (DTPA) in 1% v/v methanol solution (pH 6) as the mobile phase. Effluent from the HPLC column was delivered to the nebulizer of the ICP‐MS for the determination of thallium. The separation was complete in less than 3 min. Detection limit was 0.002 μg L^?1 for both Tl(I) and Tl(III) compounds based on peak height. The relative standard deviation of the peak areas for five injections of a mixture containing 1 μg Tl L^?1 was better than 3.4%. The concentrations of Tl compounds were determined in standard reference materials, including NIST SRM 1643e Trace Elements in Water and NRCC NASS‐5 Open Ocean Seawater and water samples collected in Kaohsiung area, Taiwan. The HPLC‐ICP‐MS results of the reference samples agreed with the reference values. This method has also been applied to determine Tl(I) and Tl(III) compounds in custard apple (Annona squamosa) leaves collected from Chai‐shan Mountain, Kaohsiung and Taitung City, Taiwan. The thallium species were quantitatively leached from the leaves with a 5 mmol L^?1 DTPA in 100 mmol L^?1 ammonium acetate solution in an ultrasonic bath during a period of 30 min. The HPLC‐ICP‐MS result that was obtained after the analysis of leaves sample showed a satisfactory agreement with the total thallium concentration obtained by ICP‐MS analysis of completely dissolved sample.     

Anodic stripping voltammetric determination of thallium as [TlBr4]-rhodamine B complex

The anodic stripping voltammetric behaviour of the [TlBr₄]-rhodamine B complex is described and compared with that of thallium(I) and thallium(III) ions. The electrolyte composition, the best potential for the deposition of thallium from the complex in the selected electrolyte, the duration of the electrolysis, and the possibility of reduction of thallium in the [TlBr₄]-rhodamine B complex before the electrolysis with ascorbic acid were investigated. The results showed good reproducibility of the measurements of thallium as [TlBr₄]-rhodamine B complex and are similar to those obtained for thallium as Tl(I) and Tl(III) ions. As the [TlBr₄]-rhodamine B complex is strongly adsorbed on polyethylene, a previous preconcentration step on a column, packed with polyethylene powder, allowed the voltammetric determination of thallium as [TlBr₄]-rhodamine B complex in samples of KCl and NaCl as solid salts after the separation of the matrix. With this procedure it was possible to reach enrichment factors of 25 with recoveries from 96.7 to 107.9% for thallium concentrations from 5 to 40 μg L^–1 and RSD between 4.2 and 9.2%. The procedure was used to determine thallium traces in KCl and in sea salt. The results of these determinations were compared with the results obtained by graphite furnace atomic absorption spectrometry. Received: 5 February 1998 / Revised: 19 May 1998 / Accepted: 29 May 1998     

The rotational spectrum and structure for the argon-cyclopentadienyl thallium van der Waals complex: experimental and computational studies of noncovalent bonding in an organometallic pi-complex

The rotational spectrum of a noble gas-organometallic complex was measured using a pulse molecular beam Fourier transform microwave spectrometer. Rotational transitions for the neutral argon-cyclopentadienyl thallium weakly bound complex were measured in the 4-9 GHz range. Analysis of the spectrum showed that the complex is a prolate symmetric-top rotor with C(5V) symmetry. The experimentally determined molecular parameters for Ar-C(5)H(5) (205)Tl are B=372.4479(3) MHz, D(J)=0.123(2) kHz, and D(JK)=0.45(2) kHz. For Ar-C(5)H(5) (203)Tl, B=373.3478(5) MHz, D(J)=0.113(3) kHz, and D(JK)=0.37(3) kHz. Using a pseudodiatomic model with Lennard-Jones potential yields an approximate binding energy of 339 cm(-1). The argon atom is located on the a-axis of the C(5)H(5)Tl monomer, directly opposite from the thallium metal atom. The measured separation distance between argon and the cyclopentadienyl ring is R=3.56 A. The overall size of the cluster is about 6 A, measuring from argon to thallium. Relatively small D(J) and D(JK) centrifugal distortion constants were observed for the complex, indicating that the structure of Ar-C(5)H(5)Tl is somewhat rigid. MP2 calculations were used to investigate the possible structures and binding energies of the argon-cyclopentadienyl thallium complex. Calculated, counterpoise corrected binding energies are evaluated at R=3.56 A for Ar-C(5)H(5)Tl range from 334 to 418 cm(-1). The experimental binding energy epsilon=339 cm(-1) for Ar-C(5)H(5)Tl falls within this range. The higher-level MP2/aug-cc-pVTZ-PP (thallium)/aug-cc-pVTZ(Ar, C, H) calculation with variable R yielded R(e)=3.46 A and binding energy of 535 cm(-1). Our estimated binding energy for argon-cyclopentadienyl thallium is very similar to the binding energy of argon-benzene. Calculations for the new van der Waals complexes, Ar(C(5)H(5)Tl)(2) and (C(5)H(5)Tl)(2), have been obtained, providing further information on the structures and bonding properties of previously observed cyclopentadienyl thallium polymer chains. The calculated intermolecular distance R(Tl-Cp)=3.05 A for the (CpTl)(2) chain subunit (Cp is cyclopentadienyl, C(5)H(5)) is slightly longer than the measured x-ray value R(M-Cp)(M=Tl)=2.75 A. The x-ray distance R(Tl-Tl)=5.5 A for the chain structure is almost identical to the calculated R(Tl-Tl)=5.51 A for the (C(5)H(5)Tl)(2) dimer.     

Studies with dithizone : Part 26. The interaction of thallium(III) with solutions of dithizone in organic solvents

The strong oxidising capacity of thallium(III) dominates its reaction with solutions of dithizone (H₂Dz) in organic solvents. When carbon tetrachloride is used as solvent, the unstable thallium(III) complex Tl(HDz)³ is found in the organic phase but it very quickly disproportionates to the thallium(I) complex [Tl(HDz)], and bis-1,5-diphenylformazan-3-yl-disulphide. This reaction is notably faster in chloroform, in which thallium(I) dithizonate is the first identifiable product. In contact with an acidic aqueous phase, thallium(I) dithizonate is reverted to regenerate dithizone in the organic phase and Tl⁺ ions appear in the aqueous phase. Organic solutions of the disulphide disproportionate spontaneously by first-order kinetics to give an equimolar mixture of dithizone and the mesoionic compound, 2,3-diphenyl-2,3-dihydrotetrazolium-5-thiolate: this change is much slower in carbon tetrachloride than in the more polar chloroform and is catalysed by both Tl⁺ and Tl³⁺. If thallium(III) is present in excess, the mesoionic compound is the principal oxidation product of the dithizone although a dication may also be formed. The mesoionic compound does not react with thallium(I) but forms a water-soluble 2:1 complex with thallium(III); partition of this complex into the organic phase is uninfluenced by chloride ions. Because of the large number of competing reactions, the composition of the reaction mixture at any stage of the reaction between thallium(III) and dithizone depends on the relative concentrations of the components, the order in which they are brought together, the time elapsed after mixing, the pH of the aqueous phase, and the nature of the organic solvent.     

Indirect Speciation Analysis of Thallium in Plant Extracts by Anodic Stripping Voltammetry

A sensitive voltammetric method (DPASV) was developed for the determination of Tl(I) and Tl(III) in plant extracts. To limit the influence of the organic matrix on the measurements, UV irradiation and addition of Amberlite XAD‐7 resin was studied. The application of 0.5 g of the resin allowed defining thallium speciation in 10.0 mL of a solution containing 0.20 mL of Sinapis alba extract. The quantification limit of 0.5 ng mL^?1 Tl(I) was found for only 10 min of preconcentration, and is low enough to allow dilution of the sample before thallium determination. The procedure was validated using the recovery study and intermethod comparison with HPLC ICP MS.