Tc Atom Research Articles

Electronic properties of titanium dioxide nanotubes doped with 4d metals

The effect of 4d-metal dopants on the densities of states of hexagonal TiO2 nanotubes has been calculated by the linearized augmented cylindrical wave method. It has been demonstrated that the substitution of Nb, Mo, Tc, or Pd atoms for a part of Ti atoms leads to a decrease in the band gap width of the material due to the formation of impurity levels in the band gap of TiO2. Doping TiO2 nanotubes with these metals is a promising way to produce materials for electrodes for electrochemical photolysis of water. Doping with Y, Rh, or Ag leads to the displacement of the absorption edge from the UV to the visible range owing to a considerable broadening of the valence and conduction band edges; Zr, Ru, and Cd have a lower disturbing effect on the electronic levels of TiO2.

Redetermination of the crystal structure of NaTcO4 at 100 and 296 K based on single-crystal X-ray data.

The redetermination of the title compound, sodium pertechnate, from single-crystal CCD data recorded both at 296 and 100 K confirms previous studies based on X-ray powder diffraction film data [Schwochau (1962 ▸). Z. Naturforsch. Teil A, 17, 630; Keller & Kanellakopulos (1963 ▸). Radiochim. Acta, 1, 107-108] and neutron powder diffraction data using the Rietveld method [Weaver et al. (2017 ▸). Inorg. Chem.12, 677-681], but reveals a considerable improvement in precision. The standard uncertainties of the room-temperature structure determination are about seven times lower than those of the neutron diffraction structure determination and about 13 times lower at 100 K, due to the decrease in the amplitude of librations. The crystal expansion could be approximated linearly with a thermal volumic expansion coefficient of 1.19 (12) × 10-4 K-1. NaTcO4 adopts the scheelite (CaWO4) structure type in space group type I41/a with Na and Tc atoms (both with site symmetry -4) replacing Ca and W atoms, respectively.

Specific features of the cis labilization effect in the series of pentacarbonyltechnetium halides

Causes of abnormal (from the viewpoint of traditional views on the cis labilization effect) enhancement of the tendency of pentacarbonyltechnetium halides to decarbonylation in the series I–Br–Cl–F are discussed. Two possible causes are considered: “nonclassical” halogen···cis-C interaction and electrostatic interactions of the halide ligand with the Tc atom in the initial complex and pentacoordinate transition state. Relative stabilization of the transition state due to electrostatic interactions is concluded to be the most probable cause of the observed trend.

Chemical Trends in Solid Alkali Pertechnetates.

Insight into the solid-state chemistry of pure technetium-99 (99Tc) oxides is required in the development of a robust immobilization and disposal system for nuclear waste stemming from the radiopharmaceutical industry, from the production of nuclear weapons, and from spent nuclear fuel. However, because of its radiotoxicity and the subsequent requirement of special facilities and handling procedures for research, only a few studies have been completed, many of which are over 20 years old. In this study, we report the synthesis of pure alkali pertechnetates (sodium, potassium, rubidium, and cesium) and analysis of these compounds by Raman spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS), solid-state nuclear magnetic resonance (static and magic angle spinning), and neutron diffraction. The structures and spectral signatures of these compounds will aid in refining the understanding of 99Tc incorporation into and release from nuclear waste glasses. NaTcO4 shows aspects of the relatively higher electronegativity of the Na atom, resulting in large distortions of the pertechnetate tetrahedron and deshielding of the 99Tc nucleus relative to the aqueous TcO4-. At the other extreme, the large Cs and Rb atoms interact only weakly with the pertechnetate, have closer to perfect tetrahedral symmetry at the Tc atom, and have very similar vibrational spectra, even though the crystal structure of CsTcO4 is orthorhombic while that of RbTcO4 is tetragonal. Further trends are observed in the cell volume and quadrupolar coupling constant.

The Magnetic Transition of Tcn (n = 1, 2) Induced by the Reaction with Cl and BO2

The Becke’s three parameter hybrid change functional based on the density functional theory method is used to investigate the magnetic transition of Tcn (n = 1, 2) induced by the reaction with Cl and BO2. Simply, the two Tc atoms in the Tc2 dimer are FM coupled, but undergoes antiferromagnetic transition when ionized to the Tc 2 + state. Interestingly, both Cl and BO2, due to their highly electronegative character, can draw electrons from the Tc2 dimer, leaving them in cationic states, therefore, the antiferromagnetic transition can also be induced when Tcn (n = 1, 2) reacts with Cl or BO2. The two Tc atoms are antiferromagnetic coupled in the neutral Tc2Cl, Tc2BO2, (Tc2Cl)2, and anionic (Tc2Cl)2, however are ferromagnetic coupled in Tc2Cl− and Tc2BO2 −. The ability to induce a magnetic transition through a chemical reaction provides a way to synthesize new magnetic materials.

The nature of the volatile technetium species formed during vitrification of borosilicate glass

Vitrification of sodium pertechnetate into borosilicate glass was performed in air at 1100 °C. A glass with a composition similar to the one developed for vitrification of the low activity waste at the Hanford site was used. A red volatile species was observed above 600 °C. The extended X-ray absorption fine structure results indicate the environment of the absorbing Tc atom consists of 2.9(6) O atoms at 1.73(2) A, 2.2(4) O atoms at 2.02(2) A, and 0.8(2) O atoms at 2.18(2) A. The results are consistent with the presence of a mononuclear species with a structure closely related to TcO3(OH)(H2O)2.

A DFT investigation on the electronic properties of octahaloditechnetate anions: Correlation between charge and bond strength

Density functional theory (DFT) calculations using BH&HLYP, B3LYP, OPBE, SVWN, BP86, BLYP, HCTH, O3LYP, X3LYP, TPSS, OLYP, PBE, and TPSSh functionals with a variety of basis sets were conducted on octahalodimetalate anions M2X8n− (M=Tc, Re, Mo; X=Cl, Br; n=2–4). The purpose of the study was to investigate the abnormal Tc2X8n− system, where the Tc–Tc bond length unexpectedly shortened from Tc2X82− to Tc2X83−, as the decrease in formal bond order from 4 to 3.5 normally tends to result in an increased bond length. Geometry optimizations using the functional BH&HLYP and basis sets SDD/aug-CC-PVDZ were able to reproduce this irregular change in Tc–Tc bond length. Natural bond orbital (NBO) analyses demonstrated that an increase in both σ and π bond strength, likely induced by the change in charge on the Tc atoms, resulted in the shortening in the Tc–Tc bond length. This study also suggested that DFT calculations on compounds with metal–metal bonds are sensitive to the choice of functionals and basis sets.

Near-threshold electron elastic scattering cross sections for Ta, W, Re, Mo, Tc and Rh atoms: Determination of electron affinities and Ramsauer-Townsend minima

Near-threshold electron scattering by the Ta, W, Re, Mo, Tc and Rh atoms is explored through the elastic cross sections calculated using the recent complex angular momentum method [1]. Electron affinities (EAs) are extracted and the Ramsauer-Townsend (R-T) minima are identified for each atom. Implications for the new large EAs are discussed.

Optical band gap of SrTcO3 from first-principles calculations

Although there are intensive studies on technetium oxide SrTcO 3 recently, its ground-state band structure has never been given and no consensus on its band gap is obtained. We use the generalized gradient approximation (GGA) with on-site Coulomb corrections (GGA + U) method to study its band structure and the optical band gap. A series of on-site interaction U and J values are employed in the calculations and the concomitant evolutions of the electronic structure, local magnetic moment of technetium ( Tc ), the exchange constant and the Néel temperature are investigated. The inter-site exchange constant between antiferromagnetic Tc atoms through medium oxygen is found to increase firstly and then decrease with an increasing U, in agreement with the trend obtained by tight-binding method. The appropriate on-site U and J values are calibrated by comparing the calculated local magnetic moment of Tc with the experimental value. It is found that when U = 2.3 eV, J = 0.3 eV are included for Tc 4d in GGA + U calculations, the local magnetic moment of Tc in orthorhombic SrTcO 3 is 2.01 μB, the same as the experimental value obtained at 4 K. The calculated band structure shows that the band gap is a direct band gap with a magnitude of 1.61 eV.

Structural, electronic and magnetic properties of transition metal binary alloy clusters with isoelectronic components: case study with MnmTcn, TimZrn and MnmRen

With the goal of achieving an understanding of the properties of bimetallic alloy clusters having atoms of two isoelectronic elements, we have studied the structural, electronic and magnetic properties of MnmTcn, MnmRen and TimZrn clusters with m + n = 13 (n = 0, 1, 4, 6, 9, 12, 13), using first-principles density functional calculations. MnmTcn and MnmRen represent clusters of isoelectronic series with a half-filled d shell, while TimZrn represents an isoelectronic cluster series of early transition metals. Mn-rich alloy clusters are found to prefer compact structures and isoelectronic Tc-rich or Re-rich alloy clusters are found to adopt open structures. In contrast, TimZrn clusters are all found to stabilize in compact structures, irrespective of being Ti-rich or Zr-rich. This change in behavior between two isoelectronic series is found to be driven by differences in hybridization effects, due to differences in the evolution of the relative energy positions of the d level with respect to the s and p levels upon moving from 3d to 4d or 5d elements. This effect further competes with the magnetization effect to decide the morphology of the alloy clusters. Focusing on the magnetic properties of the studied clusters, we find that the single Tc atom substituted alloy cluster exhibits markedly improved magnetic properties compared to that of pure Mn clusters.

On the nature of heptavalent technetium in concentrated nitric and perchloric acid

The speciation of Tc(+7) was performed in HClO4 and HNO3 by 99-Tc NMR, UV–Vis and XAFS spectroscopy. The speciation of Tc(+7) depends on the concentration and strength of the acid. Pertechnetic acid, HTcO4, forms above 8M HClO4 while in concentrated HNO3, [TcO4]− is still the predominant species. EXAFS spectroscopy shows that the structure of HTcO4 in HClO4 is similar to the one in H2SO4. The reactivity of Tc(+7) was analyzed in the frame of the partial charge model. The partial charge calculated on the Tc atoms (ΔTc) indicates that HTcO4 (ΔTc=+057) is more electrophilic than [TcO4]− (ΔTc=+0.52). The difference in the oxidizing properties between [TcO4]− and HTcO4 is given from the reaction of these species with 12M HCl(aq). In 13M sulfuric acid HTcO4 is reduced to Tc(+5) while [TcO4]− is not reduced in 6M H2SO4.

On the Structure of β-Molybdenum Dichloride

The structure of β-molybdenum dichloride is compared with that of TcCl(2) using EXAFS spectroscopy. For TcCl(2), the Tc atom is surrounded by Tc atoms at 2.13(2), 3.45(3), 3.79(4), and 4.02(4) Å. For β-MoCl(2), the Mo is surrounded by Mo atoms at 2.21(2), 2.91(3), and 3.83(4) Å. The latter distances are consistent with the presence of an [Mo(4)Cl(12)] unit in the solid state, one constituted by two triply Mo-Mo-bonded [Mo(2)Cl(8)] units. First-principles calculations show that β-MoCl(2) with the TcCl(2) "structure type" is less stable than α-MoCl(2) (Mo(6)Cl(12)) or [Mo(4)Cl(12)] edge-sharing clusters.

Magnetic exchange interactions and antiferromagnetism ofATcO3(A=Ca, Sr, Ba) studied from first principles

The magnetic properties of ATcO${}_{3}$ (A $=$ Ca, Sr, Ba) perovskites were studied from first principles using multiple-scattering theory. For each system, the most preferable magnetic order is antiferromagnetic where the magnetic moments of the nearest Tc atoms are aligned antiparallel to each other. In the case of CaTcO${}_{3}$ and SrTcO${}_{3}$, their recently observed antiferromagnetism is supported by our calculation of the Tc-Tc exchange coupling parameters. The N\'eel temperatures ${T}_{N}$ estimated for CaTcO${}_{3}$ and SrTcO${}_{3}$ are in a good agreement with experiment. For BaTcO${}_{3}$, which is not synthesized so far, we predict a fundamental band gap of 0.3 eV and ${T}_{N}$ below 900 K. In general, ${T}_{N}$ increases with volume expansion, whereas the presence of vacancies on both the oxygen and cation sites of ATcO${}_{3}$ should significantly suppress the critical temperature as well as the magnetic moment of Tc. Electronic correlations play a minor role in the formation of the magnetic state, although they may improve the calculated value of ${T}_{N}$.

99mTc-centered one-pot synthesis for preparation of 99mTc radiotracers

Nuclear medicine relies on two main imaging modalities: single photon emission computed tomography (SPECT) and positron emission tomography (PET). Radiopharmaceuticals (or radiotracers) are the blood stream of nuclear medicine for the diagnosis or therapy of diseases. Diagnostic radiotracers that are small molecules labelled with a gamma-emitter for SPECT or positron-emitter for PET provide a non-invasive method to assess the disease or disease states and monitor the therapeutic efficacy of a specific treatment regime. Over the past four decades, radiopharmaceutical research has been practising one-pot synthesis at the tracer level (10(-7)-10(-6) M). Many (99m)Tc radiotracers currently used in nuclear medicine are routinely prepared by following the basic principles of one-pot synthesis. Unlike traditional organic one-pot synthesis, which often involves the formation of multiple C-C and C-heteroatom bonds in a single step, the (99m)Tc-centered one-pot synthesis requires the formation of multiple coordination bonds between Tc and various donor atoms, such as N, O, S and P. This review will illustrate how the (99m)Tc-centered one-pot synthesis is utilized for routine preparations of different (99m)Tc radiotracers.

Trans-K3[TcO2(CN)4

The structure of the title compound, tripotassium trans-tetra­cyanidodioxidotechnetate(V), is isotypic with its Re analogue. The [TcO2(CN)4]3− trans-tetra­cyanido­dioxido­technetate anion has a slightly distorted octa­hedral configuration. The Tc atom is located on a center of inversion and is bound to two O atoms in axial and to four cyanide ligands in equatorial positions. The Tc—O distance is consistent with a double-bond character. The two potassium cations, one located on a center of inversion and one in a general position, reside in octa­hedral or tetra­hedral environments, respectively. K⋯O and K⋯N inter­actions occur in the 2.7877 (19)–2.8598 (15) Å range.

Structural Studies of Technetium−Zirconium Alloys by X-ray Diffraction, High-Resolution Electron Microscopy, and First-Principles Calculations

The structural properties of Tc-Zr binary alloys were investigated using combined experimental and computational approaches. The Tc(2)Zr and Tc(6)Zr samples were characterized by X-ray diffraction analysis, scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. Our XRD results show that Tc(6)Zr crystallizes in the cubic alpha-Mn-type structure (I43m space group) with a variable stoichiometry of Tc(6.25-x)Zr (0 < x < 1.45), and Tc(2)Zr has a hexagonal crystal lattice with a MgZn(2)-type structure (P6(3)/mmc space group). Rietveld analysis of the powder XRD patterns and density functional calculations of the "Tc(6)Zr" phase show a linear increase of the lattice parameter when moving from Tc(6.25)Zr to Tc(4..80)Zr compositions, similar to previous observations in the Re-Zr system. This variation of the composition of "Tc(6)Zr" is explained by the substitution of Zr for Tc atoms in the 2a site of the alpha-Mn-type structure. These results suggest that the width of the "Tc(6)Zr" phase needs to be included when constructing the Tc-Zr phase diagram. The bonding character and stability of the various Tc-Zr phases were also investigated from first principles. Calculations indicate that valence and conduction bands near the Fermi level are dominated by electrons occupying the 4d orbital. In particular, the highest-lying molecular orbitals of the valence band of Tc(2)Zr are composed of d-d sigma bonds, oriented along the normal axis of the (110) plane and linking the Zr network to the Tc framework. Strong d-d bonds stabilizing the Tc framework in the hexagonal unit cell are also in the valence band. In the cubic structures of Tc-Zr phases, only Tc 4d orbitals are found to significantly contribute near the Fermi level.

Tetraethylammonium tricarbonylchlorido(isoquinoline-1-carboxylato-κ2 N,O)technetate(I)

The asymmetric unit of the title compound, (C8H20N)[Tc(C10H6NO2)Cl(CO)3], consists of two crystallographically independent technetium complexes related via a pseudo-inversion centre and two tetra­ethyl­ammonium cations. The Tc atoms have slightly distorted octa­hedral coordination geometries, and they are linked with the cations by inter­molecular C—H⋯O and C—H⋯Cl hydrogen-bonding contacts, forming two-dimensional columns, which lie approximately parallel to (001) in the crystal structure. The isochinolate (isoquinoline-1-carboxyl­ate) ligands link the columns by partial π–π stacking [centroid–centroid distance 4.3733 (11) Å], forming a three-dimensional network structure.

Hexacarbonyl-technetium(I) perchlorate.

The title compound, [Tc(CO)6]ClO4, was synthesized by the reaction of [TcCl(CO)5] with AgClO4, followed by acidification with HClO4 under a CO atmosphere. The [Tc(CO)6]+ cation has close to idealized octa­hedral geometry, with the bond angles between cis-CO groups close to 90° and the Tc—C bond lengths in the range 2.025 (3)–2.029 (3)Å. The perchlorate anion is disordered over two crystallographically equivalent half-occupied positions. The Tc atom in the [Tc(CO)6]+ cation is located on an inversion centre.

Biodistribution of functionalized multiwall carbon nanotubes in mice

With the application of carbon nanotubes in biomedical and pharmaceutical sciences, its basic biological properties in vivo have become an issue of strong concern. Water-soluble functionalized multiwall carbon nanotubes (MWNTs) were labeled with radioactive (99m)Tc atoms, and then a tracer was used to study the distribution of MWNTs modified with glucosamine in mice. It shows that MWNTs moved easily among the compartments and tissues of the body, behaving like active molecules although their apparent mean molecular weight is tremendously large. In this study, water-soluble MWNTs were labeled with (99m)Tc for the first time, and all results on the distribution of MWNTs in animals provide useful data for their use in the biomedical field.

Correlation between X-ray chemical shift and partial charge in Tc(IV) complexes: Determination of Tc partial charge in TcnOy(4n-2y)+

The chemical shift of the X-ray absorptionK-edge of Tc(IV) complexes determined by X-ray Absorption Spectroscopy (XAS) measurement was studied. A correlation between edge position (ΔE) and partial charge on Tc atoms (δTc) was determined. This correlation was used to determinate δTcin TcnOy(4n-2y)+. Furthermore, a theoretical relation between δTcand the charge of TcnOy(4n-2y)+, was also established and the overall charge of this complex was estimated.