Thallium Centers Research Articles

Luminescence of CsCl : Tl Crystal under Synchrotron Excitation

For the first time, time-resolved emission and excitation spectra, as well as decay kinetics of luminescence of CsCl : Tl single crystals have been measured at 10 K under excitation in the 4–20 eV energy range. The results obtained confirm the earlier conclusion that the emission spectrum of the main thallium centres consists of five bands arising from the trigonal (3.88 eV) and tetragonal (3.65 eV) minima of the Tl+ triplet relaxed excited state and from the on-centre (4.56 eV), weak off-centre (≈3.0 eV), and strong off-centre (2.55 eV) configurations of an exciton localized near the Tl+ ion. The origin of the excitation bands located in the 6.0–7.8 eV energy range has been discussed. The classification of various exciton emissions in CsCl crystals with respect to the lattice relaxation performed with the use of the Kan'no method has been considered. The conclusion has been made that the on-centre self-trapped exciton emission band of CsCl should be located at (5.9 ± 0.3) eV.

Luminescence of complicated thallium centres in CsI:Tl

Emission, excitation and polarization spectra and luminescence decay kinetics have been studied for CsI:Tl single crystals with different thallium concentrations, and the spectral bands of complicated thallium centres separated. The 2.75 eV emission has been ascribed to triplet emission from dimer Tl +Tl + centres. A similar emission band has been found in polycrystalline CsI:Tl layers and is assumed to be responsible for some important characteristics of the CsI:Tl scintillator. In this paper we give an explanation of these centres and the proposed correlation of the light yield with the thallium dimer centres.

Thallium(I) complexes with modified poly(pyrazolyl)borate ligands—metal-ligand coordination and crystal packing

The structures of the thallium(I) complexes with hydrotris(pyrazolyl)borate (TpTl, 2-Tl), and the modified Bp and Tp ligands dihydrobis(1,2,4-triazolyl)borate ( 3-Tl), hydrotris(imidazolyl)borate ( 6-Tl), dihydrobis(indazolyl)borate ( 7-Tl), and hydrotris(indazolyl)borate ( 8-Tl) are reported and discussed in terms of their (molecular) metal–ligand arrangement and their crystal packing. Compounds 2-Tl and 7-Tl feature molecular TpTl and Bp′Tl units with pronounced Tl⋯π azolyl interactions between neighboring molecules. In 8-Tl the molecular units are arranged in pairs through indazolyl π⋯π stacking. Complexes 3-Tl and 6-Tl form extended 3D and 1D structures, respectively, through the bridging action of the poly(azolyl)borate ligand between three symmetry related thallium centers. Compounds 2-Tl, 3-Tl, and 8-Tl crystallize in the chiral space groups P2 1, P2 12 12 1, and C2, respectively.

The synthesis and structural characterization of bis(mercaptoimidazolyl)(pyrazolyl)hydroborato and tris(mercaptoimidazolyl)hydroborato complexes of thallium(I) and thallium(III)

The bis(mercaptoimidazolyl)(pyrazolyl)hydroborato and tris(mercaptoimidazolyl)hydroborato ligands, [pzBmMe]− and [TmPh]−, have been used to prepare complexes of both thallium(I) and thallium(III), namely [pzBmMe]Tl, [pzBmMe]TlMe2, {[TmPh]2Tl}2 and {[TmPh]2Tl}[ClO4]. For example, reaction of [pzBmMe]Tl with Me2TlCl yields [pzBmMe]TlMe2, while reaction of [TmPh]Li with Tl(ClO4)3 yields {[TmPh]2Tl}[ClO4]. [pzBmMe]TlMe2, {[TmPh]2Tl}2 and {[TmPh]2Tl}[ClO4] have been structurally characterized by X-ray diffraction. Interestingly, for the monomeric thallium(III) derivatives, the pyrazolyl group does not coordinate to the thallium center in the dimethyl complex [pzBmMe]TlMe2, which is therefore fur-coordinate, whereas all the mercaptoimidazolyl groups coordinate to thallium in {[TmPh]2Tl}+, thereby resulting in a six-coordinate octahedral geometry.

Encapsulation of Thallium(I) by Tetranuclear Rhodium or Iridium Complexes: Synthesis and Molecular Structure of Heterobimetallic Complexes Stabilized by s2−d8 Bonding Interactions

Reactions of [M4(μ-pyS2)2(cod)4] (M = Rh, Ir; pyS2 = 2,6-pyridinedithiolate, cod = 1,5-cyclooctadiene) with equimolar amounts of TlPF6 give the heterobimetallic complexes [TlM4(μ-pyS2)2(cod)4][PF6]. An outstanding change in the coordination modes of the bridging ligands occurs on the incorporation of the Tl atom into the tetranuclear complexes with the concomitant formation of two unprecedented Tl−Rh bonds. The X-ray structure of the cation [TlRh4(μ-pyS2)2(cod)4]+ (3+) shows an almost linear Rh−Tl−Rh bonded subunit with Tl−Rh separations of 2.7686(9) and 2.7706(9) Å. An unusual sawhorse coordination environment of the thallium atom is completed by binding to two pyridine nitrogen atoms. Theoretical calculations on this Rh−Tl interaction also support the formation of Rh−Tl bonds, which is accompanied by a slight electron transfer from thallium to both “Rh(cod)” fragments. An additional partial oxidation of the thallium center agrees with the large shift low field of the resonance (observed at 2926 ppm) in the 205Tl{1H} NMR spectrum of [TlRh4(μ-pyS2)2(cod)4][PF6] (3) at 273 K. Moreover, complex 3 undergoes two irreversible one-electron anodic processes at 0.52 and 0.93 V (CH2Cl2, 0.1 V s-1). These waves are shifted to higher potential than those of the parent complex [Rh4(μ-pyS2)2(cod)4]. In addition, the cathodic response of this complex shows an irreversible reduction process at −1.48 V in which the Tl+ ion is extruded. Interestingly, upon excitation in the solid state at 77 K, complex 3 shows strong luminescence which can be related to the Rh−Tl−Rh chromophore.

The Structure of Hydrotris(pyrazolyl)boratothallium(I)

The title compound crystallizes in the monoclinic space group P21 with a = 7.928(6), b = 9.306(4), c = 17.16(2) Å, β = 92.06(8)°, V = 1265(2) Å3, Z = 2, Dcalc = 2.191 g cm–3. From two independent molecular units, metal-ligand strands are formed based on electrostatic interactions between the thallium centers and pyrazolyl π manifolds from neighboring molecules.

Luminescence of a thallium-perturbed on-centre self-trapped exciton in CsCl:Tl crystal

In the luminescence spectrum of a thallium centre in CsCl:Tl crystal, besides two ultraviolet bands of the Tl + ion and two visible bands belonging to the off-centre self-trapped exciton perturbed by the Tl + ion, an additional band peaking at 4.56 eV has been observed at the 6.1 eV excitation. The decay kinetics and polarization of this emission have been studied. On the basis of the results obtained, the 4.56 eV emission is ascribed to a type I (on-centre) self-trapped exciton perturbed by the Tl + ion.

Molecular structure of acetato meso-tetra (4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(OAc), and 13C NMR investigation of its homolog cyano meso-tetra (4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(CN)

Abstract The new compound acetato meso -tetra(4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(OAc), has been synthesized and its molecular structure determined by X-ray analysis. The displacement of the thallium atom from the porphyrin mean plane was 0.808A˚. The geometry around the thallium centre of the Tl(tmpp)(OAc) molecule has Tl-O(1) = 2.29(1) and Tl-O(2) = 2.48(1) and average Tl-Np= 2.211(8)A˚. An asymmetric-bidentate acetato group is coordinated to the thallium(III) atom. The free energy of activation ΔG 224 * for the acetato group of Tl(tmpp)(OAc) in CD 2 Cl 2 solvent undergoing intramolecular exchange has been derived to be 48.4 kJ mol −1 through 1 H NMR temperature-dependent measurements. In the intermediate exchange region, neither the carbonyl nor methyl signals of the acetate ligand for Tl(tmpp)(OAc) in CD 2 Cl 2 solvent in 13 C NMR spectra was found at 20°C. In the slow exchange region, the methyl and carbonyl carbons of the acetato group are separately located at 17.7 ppm [with 3 J (Tl- 13 C) coupling constant 275 Hz] and 173.9 ppm [with 2 J (Tl- 13 C) coupling constant 230 Hz], respectively, for the Tl(tmpp)(OAc) in CD 2 Cl 2 at −90°C. The 13 C resonance of the axial cyano ligand in the title compound cyano meso -tetra(4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(CN), was observed at 139.9 ppm (20°C) [with 1 J ( 205 Tl- 13 C) coupling constant 5287.3 Hz and 1 J ( 203 Tl- 13 C) coupling constant 5238.0 Hz]. This indicates that the cyano group is, as cyanide type, axially coordinated to the Tl atom in Tl(tmpp)(CN).

A supramolecular motif in the solid-state structure of a difunctional thallium(i) amide defined by weak Tl···Tl attractions

K. W. Hellmann, L. H. Gade, R. Fleischer and D. Stalke, Chem. Commun., 1997, 527 DOI: 10.1039/A607701C

Effect of magnetic field on the decay kinetics of triplet luminescence of the selftrapped exciton perturbed by Tl + ion in thallium-doped cesium halides

Decay kinetics of visible emission of thallium centre in CsCl : Tl, CsBr : Tl and CsI : Tl crystals is studied in the magnetic field B | [0 0 1] at 0.35–0.45 K. Our previous interpretation of this emission as the triplet luminescence of the self-trapped exciton perturbed by Tl + ion is confirmed. However, the detailed structure of the corresponding relaxed excited state is found to be much more complicated than that concluded before.

Relaxed excited state structure and luminescence of thallium-doped caesium chloride and bromide

Four bands, all belonging to the main thallium centres, have been detected in the emission spectra of CsCl:Tl and CsBr:Tl crystals. Their spectral, polarization and kinetic characteristics have been studied from 0.45 up to 360 K. It has been shown that the new model proposed by us recently for the relaxed excited state (RES) structure of the luminescence centre in CsI:Tl crystals is valid for CsCl:Tl and CsBr:Tl crystals as well. Two ultraviolet emission bands excited mainly in the A absorption band of centres are ascribed to electronic transitions from trigonal and tetragonal Jahn - Teller minima of the triplet RES of . Two visible bands excitable mainly in the higher energy absorption bands of CsCl:Tl and CsBr:Tl are connected with two different off-centre configurations of self-trapped exciton perturbed by the ion. The parameters of the corresponding excited state minima have been calculated. The mixing of the impurity and halogen excited states has been shown to decrease markedly in the sequence of anions .

Coordination Complexes of Thallium (III) Chloride

X-ray crystal structures are reported for two coordination complexes of thallium(III) chloride. In the neutral, monomeric complex [TlCl3(dmpu)2] (dmpu = N,N′-dimethyl-propylene urea), the coordination geometry around the thallium centre is essentially trigonal bipyramidal with equatorial chlorines and axial dmpu ligands similar to a number of other bis-ligand complexes previously characterised; crystal data, orthorhombic, space group Fdd2, a = 17.632(2), b = 27.257(3), c = 8.0353(9) A, D calc = 1.951 Mg/m3, R = 0.028. With the chelating ligand dppmO2 (Ph2P(O)CH2P(O)Ph2), the ionic compound [TlCl2(dppmO2)2] [TlCl4] · 2thf is obtained, which comprises an octahedrally coordinated thallium cation with trans chlorines and a tetrahedral [TlCl4]− anion; crystal data, triclinic, space group P 1, a = 10.7067(9), b = 16.190(2), c = 19.114(2) A, α = 103.55(1), β = 93.710(8), γ = 95.98(1)°, D calc = 1.664 Mg/m3, R = 0.090.

ESR of Tl 2+ ions in alkali nitrates

ESR spectra of paramagnetic thallium centers in γ-irradiated powders of thallium doped alkali nitrates are studied at 77 K. Tl 2+ centers are formed due to γ-irradiation at 77 K. Principal g- and A-values are calculated. In RbNO 3, two chemically inequivalent sites are observed at 77 K. The s- and p-character of Tl 2+ have been calculated.

Peculiarities of the triplet relaxed excited state structure in thallium-doped cesium halide crystals

Abstract Four bands, all belonging to the main thallium centre, are detected in the triplet luminescence spectrum of thallium-doped cesium halides under excitation in impurity absorption bands. Their spectral, polarization and kinetics characteristics are studied at 0.35 to 360 K. The parameters of the corresponding relaxed excited states (RES) minima are calculated. Two ultraviolet emission bands are ascribed to electronic transitions from trigonal and tetragonal Jahn-Teller minima of the triplet RES of Tl+ ion. Two visible bands are assumed to arise from two different off-centre configurations of a self-trapped exciton perturbed by Tl+ ion.

Peculiarities of the triplet relaxed excited-state structure and luminescence of a CsI:Tl crystal

Four emission bands, all belonging to the main thallium centres, have been detected in CsI:Tl, and their spectral, polarization and kinetic characteristics have been studied at 0.35-320 K. A new model is proposed for the excited states responsible for the luminescence of thallium-doped caesium iodide. In this model, the main thallium centre is considered as a cluster consisting of a Tl+ ion and at least 12 I- and 11 Cs+ ions. Two weak ultraviolet emission bands of CsI:Tl (3.31 and 3.09 eV) are ascribed to electronic transitions from trigonal and tetragonal Jahn-Teller minima of the triplet relaxed excited state, whose structure is similar to that of Tl+ centres in FCC alkali halides. Two intense visible bands (2.55 and 2.25 eV) are assumed to arise from two different ("weak" and "strong") off-centre configurations of a selftrapped exciton perturbed by the TI+ ion. The minima responsible for all the emission bands are located on the same adiabatic potential energy surface. The excitonic-like nature of visible emission could explain the high scintillation efficiency of CsI:Tl.

Molecular structure of meso-tetra(4-pyridyl) porphyrinatothallium(III) acetate, Tl(tpyp)(OAc)

The molecular structure of meso-tetra(4-pyridyl)porphyrinatothallium(III) acetate, Tl(tpyp)(OAc), has been determined by X-ray analysis. The displacement of the thallium atom from the porphyrin mean plane was 0.858 Å. The geometry around the thallium centre of the Tl(tpyp)(OAc) molecule has TlO(1) = 2.266(10), TlO(2) = 2.512(9) and average TlN = 2.224(8) Å. This X-ray diffraction data provides evidence for an asymmetric pseudo-chelating acetato group coordinated to the thallium(III) atom. This might explain why intermolecular acetate exchange is the chief exchange mechanism for Tl(tpyp)(OAc).

Univalent metal ion α-hydroxy and interactions: Part 9. Preparation and crystal structures of lithium hydrogen (+)-tartrate monohydrate, potassium (+)-tartrate hemihydride and thallium(I) (+)-tartrate

The univalent metal ion compounds of (+)-tartaric acid, lithium hydrogen (+)-tartrate monohydrate ( 1), potassium (+)-tartrate hemihydrate ( 2) and thallium (+)-tartrate ( 3) have been prepared and their structures determined by X-ray diffraction methods. All form network polymer structures similar to the other group one metal tartrates. However, ( 1) is based on a dimeric repeating unit, with two independent but different five-coordinate square pyramidal lithium centres, [LiO, 1.971–2.322(8) Å]. Although both centres involve (+)-tartrate residues in α-hydroxycarboxyl bis-coordinate interactions, one centre has two, the other has one and is also coordinated to both waters (one bridging). The protonated carboxylic acid groups are uncoordinated but hydrogen bonded in both inter- and intra-dimer associations. Potassium (+)-tartrate hemihydrate ( 2) has two independent and different distorted octahedral potassium centres. About the first, there are five oxygens from (+)-tartrate residues and one from a water which bridges to another symmetry generated potassium. The second potassium has six bonds to (+)-tartrate oxygens, including a β-hydroxycarboxyl chelate ring, with a KO range of 2.711(2)–2.988(3) Å. An unusual feature is a carboxyl oxygen giving a three-centre bonding system to three separate potassium ions. The polymeric structure of thallium(I) (+)-tartrate ( 3) is based upon two different five-coordinate thallium centres [TlO range, 2.59(3)–2.96(2) Å]. About one, bonds are to three oxygens from one (+)-tartrate residue (one carboxyl, two hydroxyl), and two from a symmetric bidentate-carboxylato-(O,O′) group of a bridging (+)-tartrate. The bonded hydroxyl also bridges to the second Tl [Tl⋯Tl, 3.519(2) Å]. Completing the bonding to this second Tl are oxygens from four different tartrate residues. Crystallographic and analytical data are also provided for silver(I) (+)-tartrate ( 4).

A new model for the visible emission of the CsI: Tl crystal

Four emission bands, all belonging to the main thallium centre, are detected in a CsI:Tl crystal and their spectral, polarization and kinetic characteristics are studied at 1.7 to 320 K. Two weak ultraviolet bands (3.31 and 3.09 eV) are ascribed to electronic transitions from trigonal and tetragonal Jahn-Teller minima of the triplet relaxed excited state of Tl +. Two intense visible bands (2.55 and 2.25 eV) are assumed to arise from two different off-centre configurations of a self-trapped exciton perturbed by the Tl + ion.

Synthesis of [Tl 4Se 16] 4−: a novel tetranuclear Tl 3+ polyselenide

(Ph 4P) 4[Tl 4Se 16] was prepared hydrothermally in a sealed pyrex tube by the reaction of TlCl, K 2Se 4 and Ph 4PCl in a 1:1:1 molar ratio at 110 °C for one day. The red crystals were obtained in 50% yield. Crystals of (Ph 4P) 4[Tl 4Se 16]: triclinic P 1 (No. 2), Z=1, a=12.054(9), b=19.450(10), c=11.799(6) Å, α=104.63(4), β=98.86(6), γ=101.99(6)° and V=2555(3) Å 3 at 23 °C, 2θ max=40.0°, μ=120.7 cm −1, D calc=2.23. The structure was solved by direct methods. Number of data collected: 5206. Number of unique data having F o 2>3σ( F o 2): 1723. Final R=0.075 and R w=0.089. [Tl 4Se 16] 4− consists of four, almost already linearly arranged, tetrahedral thallium centers which are coordinated by two chelating Se 4 2−, two bridging Se 2 2− and four bridging Se 2− ligands. [Tl 4Se 16] 4− sits on an inversion center and possesses a central {Tl 2Se 2} 2+ planar core. The Tl(1)–Tl(1)′ distance in this core is 3.583(6) Å. These two thallium atoms are then each linked to two cyclic Tl(Se 4) fragments via bridging Se 2 2− and Se 2− ligands forming Tl 2Se(Se 2) five-membered rings.

Molecular structure of thallium(III) meso-tetraphenylporphyrin acetate: Tl(tpp)(OAc)

X-ray diffraction data and solid-state 13C CP/MAS spectra of thallium(III) mesotetraphenylporphyrin acetate, Tl(tpp)(OAc), provide evidence for a chelating-bidentate acetato group coordinated to the thallium(III) atom. The displacement of the thallium atom from the porphyrin mean plane was 0.842 Å. The geometry around the thallium centre of the Tl(tpp)(OAc) molecule has TlO(1) = 2.361(9), TlO(2) = 2.229(10) and TlN = 2.219(7) Å. Fourier-transform IR spectra (400–4000 cm −1) of Tl(tpp)(OAc) in KBr discs and in CH 2Cl 2 solvent are reported and assigned by comparison with the spectra of Tl(tpp)(CN). It is concluded that the intramolecular exchange of the acetato group between asymmetric pseudo-chelating c and d result in the adaptation of the chelating bidentate, a for the carboxylate at low temperature and that of the symmetric pseudochelating b at high temperature for Tl(tpp)(OAc) in CH 2Cl 2 solvent. This explains the resonances of 13C and 1H of the axial acetato group in low- and high-temperature solution NMR measurements.