Syntheses; 77Se, 203Tl, and 205Tl NMR; and theoretical studies of the Tl2Se6(6-), Tl3Se6(5-), and Tl3Se7(5-) anions and the X-ray crystal structures of [2,2,2-crypt-Na]4[Tl4Se8].en and [2,2,2-crypt-Na]2[Tl2Se4](infinity)1.en

The 2,2,2-crypt salts of the Tl4Se8(4-) and [Tl2Se4(2-)]infinity1 anions have been obtained by extraction of the ternary alloy NaTl0.5Se in ethylenediamine (en) in the presence of 2,2,2-crypt and 18-crown-6 followed by vapor-phase diffusion of THF into the en extract. The [2,2,2-crypt-Na]4[Tl4Se8].en crystallizes in the monoclinic space group P2(1)/n, with Z = 2 and a = 14.768(3) angstroms, b = 16.635(3) angstroms, c = 21.254(4) angstroms, beta = 94.17(3) degrees at -123 degrees C, and the [2,2,2-crypt-Na]2[Tl2Se4]infinity1.en crystallizes in the monoclinic space group P2(1)/c, with Z = 4 and a = 14.246(2) angstroms, b = 14.360(3) angstroms, c = 26.673(8) angstroms, beta = 99.87(3) degrees at -123 degrees C. The TlIII anions, Tl2Se6(6-) and Tl3Se7(5-), and the mixed oxidation state TlI/TlIII anion, Tl3Se6(5-), have been obtained by extraction of NaTl0.5Se and NaTlSe in en, in the presence of 2,2,2-crypt and/or in liquid NH3, and have been characterized in solution by low-temperature 77Se, 203Tl, and 205Tl NMR spectroscopy. The 1J(203,205Tl-77Se) and 2J(203,205Tl-203,205Tl) couplings of the three anions have been used to arrive at their solution structures by detailed analyses and simulations of all spin multiplets that comprise the 205,203Tl NMR subspectra arising from natural abundance 205,203Tl and 77Se isotopomer distributions. The structure of Tl2Se6(6-) is based on a Tl2Se2 ring in which each thallium is bonded to two exo-selenium atoms so that these thalliums are four-coordinate and possess a formal oxidation state of +3. The Tl4Se8(4-) anion is formally derived from the Tl2Se6(6-) anion by coordination of each pair of terminal Se atoms to the TlIII atom of a TlSe+ cation. The structure of the [Tl2Se4(2-)]infinity1 anion is comprised of edge-sharing distorted TlSe4 tetrahedra that form infinite, one-dimensional [Tl2Se42-]infinity1 chains. The structures of Tl3Se6(5-) and Tl3Se7(5-) are derived from Tl4Se4-cubes in which one thallium atom has been removed and two and three exo-selenium atoms are bonded to thallium atoms, respectively, so that each is four-coordinate and possesses a formal oxidation state of +3 with the remaining three-coordinate thallium atom in the +1 oxidation state. Quantum mechanical calculations at the MP2 level of theory show that the Tl2Se6(6-), Tl3Se6(5-), Tl3Se7(5-), and Tl4Se8(4-) anions exhibit true minima and display geometries that are in agreement with their experimental structures. Natural bond orbital and electron localization function analyses were utilized in describing the bonding in the present and previously published Tl/Se anions, and showed that the Tl2Se6(6-), Tl3Se6(5-), Tl3Se7(5-), and Tl4Se8(4-) anions are electron-precise rings and cages.     

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.     

First examples of thallium chalcogenide cages. Syntheses, 77Se, 203Tl, and 205Tl NMR study of the Tl4Se5(4-) and Tl4Se6(4-) anions, the X-ray crystal structure of (2,2,2-crypt-K+)3Tl5Se5(3-), and theoretical studies

The Tl5Se5(3-) anion has been obtained by extracting KTlSe in ethylenediamine in the presence of 2,2,2-crypt. The salt, (2,2,2-crypt-K+)3Tl5Se5(3-), crystallizes in the triclinic system, space group P1, with Z = 2 and a = 11.676(2) A, b = 16.017(3) A, c = 25.421(5) A, alpha = 82.42(3) degrees, beta = 88.47(3) degrees, gamma = 69.03(3) degrees at -123 degrees C. Two other mixed oxidation state TlI/TlIII anions; Tl4Se5(4-) and Tl4Se6(4-), have been obtained by extracting KTlSe into liquid NH3 in the presence of 2,2,2-crypt and have been characterized in solution by low-temperature 77Se, 203Tl, and 205Tl NMR spectroscopy and were shown to exist as a 1:1 equilibrium mixture at -40 degrees C. The couplings, 1J(203,205Tl-77Se) and 2J(203,205Tl-203,205Tl), have been observed for Tl4Se5(4-) and Tl4Se6(4-) and have been used to arrive at the solution structures of both anions. Structural assignments were achieved by detailed analyses and simulations of all spin multiplets that comprise the 205,203Tl NMR spectra and that arise from natural abundance 205,203Tl and 77Se or enriched 77Se isotopomer distributions. The structures of all three anions are based on a Tl4Se4 cube in which Tl and Se atoms occupy alternate corners. There are one and two exo-selenium atoms bonded to thallium in Tl4Se5(4-) and Tl4Se6(4-), respectively, so that these thalliums are four-coordinate and possess a formal oxidation state of +3 and the remaining three-coordinate thallium atoms are in the +1 oxidation state. The structure of Tl5Se5(3-) may be formally regarded as an adduct in which Tl+ is coordinated to the unique exo-selenium and to two seleniums in a cube face containing the TlIII atom. The Tl4Se5(4-), Tl4Se6(4-), and Tl5Se5(3-) anions and the presently unknown, but structurally related, Tl4Se4(4-) anion can be described as electron-precise cages. Ab initio methods at the MP2 level of theory show that Tl4Se5(4-), Tl4Se6(4-), and Tl5Se5(3-) exhibit true minima and display geometrical parameters that are in excellent agreement with their experimental cubanoid structures, and that Tl4Se4(4-) is cube-shaped (Td point symmetry). The gas-phase energetics associated with plausible routes to the formation and interconversions of these anions have been determined by ab initio methods and assessed. It is proposed that all three cubanoid anions are derived from the known Tl2Se2(2-), TlSe3(3-), Se2(2-), and polyselenide anions that have been shown to be present in the solutions they are derived from.     

Distribution of 201Tl in the blood

Thallium-201 distribution in the blood was investigated both in vivo and in vitro. Thallium-201 was distributed into the erythrocytes and plasma with the ratio of 1.4 +/- 0.3 to 1.0, immediately after its administration. The uptake of 201Tl into the erythrocytes in vitro were affected by the incubation temperature and the presence of ouabain and KCl; indicating that the 201Tl was uptaken into cells partly through their membranes Na, K-ATPase. Erythrocytes could retain 201Tl in it, whereas 201Tl was present as free ion in the plasma. Thallium-201 was flew out of erythrocytes into the plasma, keeping the ratio of 201Tl in erythrocytes/plasma to be 1.9 +/- 0.2/1.0.     

Solvent extraction of Tl/I/ with 2-mercaptobenzothiazole into chloroform

The extraction of Tl/I/ with 2-mercaptobenzothiazole into chloroform has been studied. The effect of various parameters on the extraction coefficient value has been evaluated. The stoichiometry of the extracted species obtained from the substoichiometric extraction was found to be 11. This war further supported by the slope ratio method. Decontamination factors of a number of elements in the substoichiometric extraction of Tl/I/ were also obtained.     

Gamma-ray spectra of 201Tl-radiopharmaceuticals with a scintillation camera--crosstalk of contaminating nuclides of 200Tl and/or 202Tl onto 201Tl-photopeaks

In cardiac imaging with 201Tl, the collimator for low energy high resolution is generally used, and also the energy window, which is set on the spectral display of a pulse height analyzer of a scintillation camera, is chosen 70 +/- 12.5 keV. The purpose of this study is to discuss those conditions in 201Tl imaging with the scintillation camera. Two types of collimators for HR (high resolution) and ME (medium energy) were used in this experiment, and we measured the pulse height spectra of 201TlCl radiopharmaceuticals in air and in a cuboid phantom, connecting a multi-channel pulse height analyzer to the scintillation camera. As a result of measuring of the pulse height spectra, two different energies of gamma rays which are not supposed to emit from 201Tl nuclide were observed, and we also identified the presence of a small amount of 202Tl (with 439 keV) and/or 200Tl (with 368 keV) from their half-life measurements. Thus, the use of the HR-collimator with 201Tl imaging is not suitable, because the shielding effects of its septa is poor to 439 keV gamma-rays, and the scattered radiation produced by the Compton interaction contributes to the principal photopeak on the pulse height spectrum. Here, we recommend the use ME-collimator instead of the HR-one, and of the window width of 76 +/- 25 keV for increasing the count rate.     

Na(23)K(9)Tl(15.3): An Unusual Zintl Compound Containing Apparent Tl(5)(7)(-), Tl(4)(8)(-), Tl(3)(7)(-), and Tl(5)(-) Anions

Reaction of the neat elements in tantalum containers at 400 degrees C and then 150 degrees C gives the pure title phase. X-ray crystallography shows that the hexagonal structure (P6(3)/mmc, Z = 2, a = 11.235(1) ?, b = 30.133(5) ?) contains relatively high symmetry clusters Tl(5)(7)(-) (D(3)(h)()), Tl(4)(8)(-) (C(3)(v)(), approximately T(d)), and the new Tl(3)(7)(-) (D(infinity)(h)()) plus Tl(5)(-), the last two disordered over the same elongated site in 1:2 proportions. Cation solvation of these anions is tight and specific, providing good Coulombic trapping of weakly bound electrons on the isolated cluster anions. The observed disorder makes the compound structurally a Zintl phase with a closed shell electron count. EHMO calculations on the novel Tl(3)(7)(-) reveal some bonding similarities with the isoelectronic CO(2), with two good sigma(s,p) bonding and two weakly bonding pi MO's. The Tl-Tl bond lengths therein (3.14 ?) are evidently consistent with multiple bonding. The weak temperature-independent paramagnetism and metallic conductivity (rho(293) approximately 90 &mgr;Omega.cm) of the phase are discussed.     

Synthesis and structure of K10Tl7: the first binary trielide containing naked pentagonal bipyramidal Tl7 clusters

The title compound is synthesized by direct fusion of the elements at 400 degrees C followed by annealing at 330 degrees C, quenching to room temperature, and subsequent annealing at 120 and 100 degrees C for days to weeks. The compound crystallizes in the monoclinic space group P21/c (No. 14), with Z = 4, a = 10.132(1) A, b = 22.323(2) A, c = 13.376(1) A, and beta = 93.14(1)degrees, and consists of Tl7(7-) clusters embedded in a matrix of potassium ions. The cluster is an axially compressed pentagonal bipyramid close to D5h symmetry. The apex-apex bond distance (3.462(1) A) is little longer than the bonds in the pentagonal waist (3.183(1)-3.247(1) A). Structurally the compound is not electron-precise: K10Tl7 has three extra electrons per Tl7 cluster and is Pauli paramagnetic (chi300 = 2.25 x 10(-4) emu/mol).     

Preferential synthesis of highly conducting Tl(TCNQ) phase II nanorod networks via electrochemically driven TCNQ/Tl(TCNQ) solid-solid phase transformation

Facile synthesis and characterization of the highly conducting, thermodynamically favored, Tl(TCNQ) phase II microrods/nanorods onto conducting (glassy carbon (GC)) and semiconducting (indium tin oxide (ITO)) surfaces have been accomplished via redox-based transformation of 7,7,8,8-tetracynoquinodimethane (TCNQ) microcrystals. This electrochemically irreversible process involves the one-electron reduction of surface-confined solid TCNQ into TCNQ·^? with concomitant incorporation of the Tl⁺ _(aq) cation, from the bulk solution, at the triple-phase boundary, GC or ITO│(TCNQ_(s)/TCNQ·^? _(s))│Tl⁺ _(aq), through a nucleation/growth mechanism. Consistent with the conceptually related M(TCNQ) systems (M⁺ = Li⁺, Na⁺, K⁺, Ag⁺, and Cu⁺), the TCNQ/Tl(TCNQ) interconversion is strongly dependent upon scan rate, Tl⁺ _(aq) electrolyte concentration, and the method of attaching solid TCNQ onto the electrode surface. Spectroscopic (infrared (IR) and Raman), microscopic (scanning electron microscopy (SEM)), and surface science (X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD)) characterization of the electrochemically synthesized material revealed formation of pure Tl(TCNQ) phase II. Importantly, the generic solid-state electrochemical approach used in this study not only offers facile protocol for controllable and preferential synthesis of Tl(TCNQ) phase II but also provides access to fabricate and tune the morphology to yield microrod/nanorod networks.

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Graphical abstract Controlled synthesis of the highly conducting Tl(TCNQ) phase II with either nanowire or rod-like morphologies is achieved via a redox-based solid-solid phase interconversion of TCNQ microcrystals in the presence of a Tl⁺ _(aq) electrolyte.

     

Pentavalent and tetravalent uranium selenides, Tl3Cu4USe6 and Tl2Ag2USe4: syntheses, characterization, and structural comparison to other layered actinide chalcogenide compounds

The compounds Tl(3)Cu(4)USe(6) and Tl(2)Ag(2)USe(4) were synthesized by the reaction of the elements in excess TlCl at 1123 K. Both compounds crystallize in new structure types, in space groups P2(1)/c and C2/m, respectively, of the monoclinic system. Each compound contains layers of USe(6) octahedra and MSe(4) (M = Cu, Ag) tetrahedra, separated by Tl(+) cations. The packing of the octahedra and the tetrahedra within the layers is compared to the packing arrangements found in other layered actinide chalcogenides. Tl(3)Cu(4)USe(6) displays peaks in its magnetic susceptibility at 5 and 70 K. It exhibits modified Curie-Weiss paramagnetic behavior with an effective magnetic moment of 1.58(1) μ(B) in the temperature range 72-300 K, whereas Tl(2)Ag(2)USe(4) exhibits modified Curie-Weiss paramagnetic behavior with μ(eff) = 3.4(1) μ(B) in the temperature range 100-300 K. X-ray absorption near-edge structure (XANES) results from scanning transmission X-ray spectromicroscopy confirm that Tl(3)Cu(4)USe(6) has Se bonding characteristic of discrete Se(2-) units, Cu bonding generally representative of Cu(+), and U bonding consistent with a U(4+) or U(5+) species. On the basis of these measurements, as well as bonding arguments, the formal oxidation states for U may be assigned as +5 in Tl(3)Cu(4)USe(6) and +4 in Tl(2)Ag(2)USe(4).     

Tl2D coordination polymer involving close Tl?π (aromatic) contacts, [Tl3(μ-BPC)2(μ-NO3)]n

A two-dimensional polymer, [Tl₃(μ-BPC)₂(μ-NO₃)]_n [BPC = biphenyl-2-carboxylate], has been synthesized and characterized. Its single-crystal X-ray structure shows three types of Tl^I-ions with coordination numbers of 5 (Tl1 and Tl2), and 4 (Tl3). Two of the thallium atoms, Tl1 and Tl3, contain close Tl^I?π (aromatic) contacts, thus attaining a total hapticity of 11 and 10 with environments Tl1O₅C₆ and Tl3O₄C₆, respectively.     

Structures and properties of the ternary thallium chalcogenides Tl2MQ3 (M = Zr, Hf; Q = S, Se)

We have synthesized new compounds of the formula Tl(2)MQ(3), with M = Zr and Hf and Q = S and Se, and studied their crystallographic features, electronic structures and electrical conductivity. These isostructural compounds crystallize in the monoclinic space group P2(1)/m (Z = 2), with unit cell parameters for the representative Tl(2)ZrS(3) of a = 7.9159(10) ?, b = 3.7651(5) ?, c = 10.275(2) ?, and β = 97.476(2)°. The Zr atoms of Tl(2)ZrS(3) are (distorted) octahedrally coordinated by the S atoms, with two such octahedra sharing edges along the c axis and forming infinite double chains running parallel to the b axis. Tl atoms separate these chains from one another along the a and c axes. The Tl atoms are also surrounded by S atoms in a distorted octahedral coordination. The structure may be viewed as alternating layers of Zr/Tl atoms and S atoms, and is therefore a distorted, ordered variant of the α-NaFeO(2) structure type. All atoms are in their standard oxidation states: Tl(+), Zr(4+), S(2-). The sulphide Tl(2)ZrS(3) has a calculated band gap of 1.15 eV, and the selenide Tl(2)HfSe(3) a gap of 0.57 eV. The electrical conductivity values of Tl(2)ZrS(3) and Tl(2)HfSe(3) at room temperature are 7.1 × 10(-6)Ω(-1) cm(-1) and 3.9 × 10(-3)Ω(-1) cm(-1), respectively.     

Study of formation of aqueous Tl/Ag bimetallic clusters by gamma and electron irradiation

The UV–visible spectral characteristics of the Ag, Tl and bimetallic Tl/Ag clusters stabilized by polyethylene glycol and produced by radiation-induced reduction using both gamma and electron irradiation, have been studied in aqueous medium. A comparison of the two reduction methods, suggested that the high dose rate conditions of electron irradiation resulted in intimately alloyed mixed clusters with almost no aggregation at higher dose. Whereas, under the lower dose rate conditions of gamma irradiation, the bimetallic clusters with core of Ag and shell of Tl were formed due to the reduction of Tl⁺ ions over the initially produced Ag nanoparticles. Only the thallium part of the mixed clusters were oxidized by both methyl viologen (MV²⁺) chloride and oxygen, leaving behind absorption due to Ag nanoparticles.     

Tl2CuAsO4 – ein Zwischenprodukt bei der Oxidation von Tl/Cu/As-Legierungen im Sauerstoffstrom

Tl₂CuAsO₄ – an Intermediate Phase in the Oxidation of Tl/Cu/As Alloys with Oxygen Waxy, honey-jellow single crystals of the new compound Tl₂CuAsO₄ (monoclinic, P2₁/c, a = 860.1(1) pm, b = 533.94(7) pm, c = 1200.1(2) pm, β = 98.10(1)°, Z = 4) were prepared as an intermediate product of the oxidation process in the reaction of Tl/Cu/As-alloys with oxygen. Their structure was determined from IPDS data (w2R = 0.071 for 1271 F² values and 74 parameters). The structure contains an isolated [Cu₂As₂O₈]^4– group consisting of two AsO₄-tetrahedra connected by two Cu⁺ ions with an approximately linear O–Cu–O coordination. The [Cu₂As₂O₈]^4– groups are linked to a threedimensional framework by thallium(I) ions which show an hemispheric coordination sphere of oxygen ions indicating the stereochemical activity of the Tl⁺ lone pair.     

Quantum mechanical/molecular mechanical simulations of the Tl(III) ion in water

Classical molecular dynamics (MD) and combined quantum mechanical/molecular mechanical (QM/MM) MD simulations have been performed to investigate the structural and dynamical properties of the Tl(III) ion in water. A six-coordinate hydration structure with a maximum probability of the Tl-O distance at 2.21 A was observed, which is in good agreement with X-ray data. The librational and vibrational spectra of water molecules in the first hydration shell are blue-shifted compared with those of pure liquid water, and the Tl-O stretching force constant was evaluated as 148 Nm(-1). Both structural and dynamical properties show a distortion of the first solvation shell structure. The second shell ligands' mean residence time was determined as 12.8 ps. The Tl(III) ion can be classified as "structure forming" ion; the calculated hydration energy of -986 +/- 9 kcal mol agrees well with the experimental value of -986 kcal mol.     

Die Schichtstruktur von Tl[CuAsO4] und Tl[CuPO4] mit Zwischenschichten aus Thallium(I) mit stereoaktivem Elektronenpaar

The Layer Structure of Tl[CuAsO₄] and Tl[CuPO₄] with Layers of Thallium(I) with Stereoactive Lone Pair Single crystals of Tl[CuAsO₄] and Tl[CuPO₄] were prepared by reaction of oxygen with Tl/Cu/As and Tl/Cu/P alloys, respectively. The new isotypic compounds crystallize in spacegroup C2/c with Z = 8 and lattice constants a = 684.70(7) pm, b = 712.64(5) pm, c = 1822.4(2) pm, β = 92.76(1)° for Tl[CuAsO₄] and a = 671.57(8) pm, b = 697.09(6) pm, c = 1789.1(2) pm, β = 93.12(1)° for Tl[CuPO₄]. Square planar [CuO₄]-units are connected by common corners to form undulated [CuO₃]₂-chains running along [010]. Interconnection of the chains by arsenate or phosphate groups results in the formation of anionic cuprate-arsenate- and cuprate-phosphate-slabs, respectively. Along [001] these slabs are alternating with double layers of thallium(I) ions in which the stereochemical activity of the Tl⁺ lone pair is apparent from an hemispheric coordination of thallium by oxygen. The structure is related to that of the orthorhombic form of KCuPO₄.     

Two-electron transfer for Tl(aq)(3+)/Tl(aq)(+) revisited. Common virtual [Tl(II)-Tl(II)](4+) intermediate for homogeneous (superexchange) and electrode (sequential) mechanisms

Homogeneous and electrochemical two-electron transfers within the Tl(aq)(3+)/Tl(aq)(+) couple are considered on a common conceptual basis. For the 2 equiv electrochemical reduction of Tl(aq)(3+) to Tl(aq)(+), the intermediate state with a formal reduction potential, E(1) = 1.04 +/- 0.10 V vs the normal hydrogen electrode, was detected, different from the established value of 0.33 V for a Tl(3+)/Tl(2+) couple. Examination of obtained electrochemical (cyclic voltammetry (CV) and rotating disk electrode techniques, along with the CV-curve computer simulation procedure) and literature data indicate that the detected formal potential cannot be the property of electrode-adsorbed species, but rather of the covalently interacting dithallium intermediate [Tl(II)-Tl(II)](4+) located at the outer Helmholtz plane. The analysis of microscopic mechanisms, based on the recent hypothesis of H. Taube and the Marcus-Hush theory extended by Zusman and Beratan, and Koper and Schmickler, revealed that the homogeneous process most probably takes place through the superexchange inner-sphere two-electron-transfer mechanism, via an essentially virtual (undetectable) dithallium intermediate. In contrast, the electrochemical process occurs through a sequential mechanism, via the rate-determining step of Tl(aq)(2+) ion formation immediately followed by activationless formation of the metastable (CV-active) dithallium state. The second electrochemical electron-transfer step is fast, and shows up only in the peak height (but not in the shape) of the observed CV cathodic wave. The anodic wave for a microscopically reverse process of the oxidation of Tl(aq)(+) to Tl(aq)(3+) cannot be observed within the considered potential range due to the blocking of through-space electron transfer by the competitor process of ion transfer to the electrode.     

A(15)Tl(27) (A = Rb, Cs): A Structural Type Containing Both Isolated Clusters and Condensed Layers Based on the Tl(11) Fragment. Syntheses, Structure, Properties, and Band Structure

The isomorphous title compounds (and the ordered substitutional Rb(14)CsTl(27)) are obtained directly from reactions of the elements in sealed Ta below approximately 330 degrees C. Refinements of single-crystal data for the three established a structure with alternate layers of isolated pentacapped trigonal prismatic Tl(11)(7)(-) (D(3)(h)()) ions and condensed [Tl(16)(8-)] networks that are separated by cations. The condensed layer consists of Tl(11) units that share prismatic edges and are interbridged through waist-capping atoms (Tl(6/2)Tl(3)Tl(2)). (Rb(15)Tl(27): P&sixmacr;2m, Z = 1, a = 10.3248(6) ?, c = 17.558(2) ?.) The rubidium phase is a poor metal (rho(293) approximately 34 &mgr;Omega.cm) and is Pauli-paramagnetic. Extended Hückel band calculations indicate partially filled bands and a non-zero DOS at E(F), consistent with the observed metallic behavior, although appropriate cation tuning or modest anion doping should provide a Zintl phase. The band structure and COOP curves are also used to rationalize the distortion of the Tl(11) unit on condensation and the critical role of the interfragment bonds between waist-capping atoms in stabilizing the layer.     

Synthesis of Pd3Tl and Pd6Tl2 complexes based on a trinuclear aryl-palladium(II) complex acting as a metallaligand toward thallium(I) through Tl-arene and Tl-I bonds

The metallaligand [(PdIL(2))(3)(C(6)Me(3)-1,3,5)] (L(2) = 4,4'-di-tert-butyl-2-2'-bipyridine = tbbpy) reacts with TlOTf to afford the complex [{(PdIL(2))(3)C(6)Me(3)-1,3,5}Tl]OTf, which exists in the solid state as a 2:1 mixture of monomer and dimer, both showing Tl(I)-I and Tl(I)-η(6)-mesitylene bonds. In solution, only the monomer is observed. Heating of toluene solutions of [(PdIL(2))(3)(C(6)Me(3)-1,3,5)] affords the dinuclear complex [(PdIL(2))(2)(C(6)HMe(3)-1,3,5)].     

205Tl NMR methods for the characterization of monovalent cation binding to nucleic acids

Monovalent cations play an important role in many biological functions. The guanine rich sequence, d(G4T4G4), requires monovalent cations for formation of the G-quadruplex, d(G4T4G4)2. This requirement can be satisfied by thallium (Tl+), a potassium (K+) surrogate. To verify that the structure of d(G4T4G4)2 in the presence of Tl+ is similar to the K+-form of the G-quadruplex, the solution structure of the Tl+-form of d(G4T4G4)2 was determined. The 10 lowest energy structures have an all atom RMSD of 0.76 +/- 0.16 A. Comparison of this structure to the identical G-quadruplex formed in the presence of K+ validates the isomorphous nature of Tl+ and K+. Using a 1H-205Tl spin-echo difference experiment we show that, in the Tl+-form of d(G4T4G4)2, small scalar couplings (<1 Hz) exist between 205Tl and protons in the G-quadruplex. These data comprise the first 1H-205Tl scalar couplings observed in a biological system and have the potential to provide important constraints for structure determination. These experiments can be applied to any system in which the substituted Tl+ cations are in slow exchange with the bulk ions in solution.